Designation l in electrical circuits. Conditional graphic images of elements of electrical circuits

Introduction

The search for new energy to replace smoky, expensive, low-efficiency fuels led to the discovery of the properties of various materials to accumulate, store, quickly transmit and convert electricity. Two centuries ago, methods of using electricity in everyday life and industry were discovered, investigated and described. Since then, the science of electricity has become a separate branch. Now it is difficult to imagine our life without electrical appliances. Many of us without fear undertake to repair household appliances and successfully deal with it. Many are afraid to fix even the outlet. Armed with some knowledge, we will no longer be afraid of electricity. The processes occurring in the network should be understood and used for your own purposes.
The proposed course is designed for the initial acquaintance of the reader (student) with the basics of electrical engineering.

Basic electrical quantities and concepts

The essence of electricity is that the flow of electrons moves along a conductor in a closed circuit from a current source to a consumer and vice versa. Moving, these electrons perform a certain work. This phenomenon is called - ELECTRIC CURRENT, and the unit of measurement is named after the scientist who was the first to study the properties of current. The surname of the scientist is Ampere.
You need to know that the current during operation heats up, bends and tries to break the wires and everything through which it flows. This property should be taken into account when calculating circuits, i.e., the greater the current, the thicker the wires and structures.
If we open the circuit, the current will stop, but there will still be some potential at the terminals of the current source, always ready to work. The potential difference at the two ends of the conductor is called VOLTAGE ( U).
U=f1-f2.
At one time, a scientist by the name of Volt scrupulously studied electrical voltage and gave him detailed explanation. Subsequently, the unit of measurement was given its name.
Unlike current, voltage does not break, but burns. Electricians say - punches. Therefore, all wires and electrical units are protected by insulation, and the higher the voltage, the thicker the insulation.
A little later, another famous physicist - Ohm, carefully experimenting, revealed the relationship between these electrical quantities and described it. Now every student knows Ohm's law I=U/R. It can be used to calculate simple circuits. Having covered the value we are looking for with our finger, we will see how to calculate it.
Don't be afraid of formulas. To use electricity, it is not so much they (formulas) that are needed, but an understanding of what is happening in the electrical circuit.
And the following happens. An arbitrary current source (let's call it for now - GENERATOR) generates electricity and transmits it by wire to the consumer (let's call it, for now, with a word - LOAD). Thus, we have obtained a closed electrical circuit "GENERATOR - LOAD".
While the generator is generating energy, the load consumes it and works (i.e., converts electrical energy into mechanical, light, or any other). By putting an ordinary knife switch in the wire break, we can turn the load on and off when we need it. Thus, we get inexhaustible possibilities of regulation of work. It is interesting that when the load is off, there is no need to turn off the generator (by analogy with other types of energy - extinguish a fire under a steam boiler, turn off the water in a mill, etc.)
It is important to observe the proportions GENERATOR-LOAD. The generator power must not be less than the load power. It is impossible to connect a powerful load to a weak generator. It's like harnessing an old horse to a heavy cart. Power can always be found in the documentation for the electrical appliance or its marking on a plate attached to the side or rear wall of the electrical appliance. The concept of POWER was introduced more than a century ago, when electricity went beyond the thresholds of laboratories and began to be used in everyday life and industry.
Power is the product of voltage and current. The unit is watt. This value shows how much current the load consumes at this voltage. P=U X

electrical materials. Resistance, conductivity.

We have already mentioned a quantity called OM. Now let's dwell on it in more detail. For a long time, scientists have paid attention to the fact that different materials behave differently with current. Some let it pass without hindrance, others stubbornly resist it, others let it pass only in one direction, or let it pass “on certain conditions”. After testing the conductivity of all possible materials, it became clear that absolutely all materials, to some extent, can conduct current. To assess the "measure" of conductivity, a unit of electrical resistance was deduced and called it OM, and materials, depending on their "ability" to pass current, were divided into groups.
One group of materials is conductors. Conductors conduct current without much loss. Conductors include materials with a resistance of zero to 100 ohm/m. These properties are mainly found in metals.
Another group- dielectrics. Dielectrics also conduct current, but with huge losses. Their resistance is from 10,000,000 ohms to infinity. Dielectrics, for the most part, include non-metals, liquids and various gas compounds.
A resistance of 1 ohm means that in a conductor with a cross section of 1 sq. mm and 1 meter long, 1 ampere of current will be lost..
The reciprocal of the resistance - conductivity. The value of the conductivity of a material can always be found in reference books. Resistivity and conductivity of some materials are shown in Table No. 1

TABLE #1

MATERIAL	Resistivity	Conductivity
Aluminum
Tungsten
Platinum-iridium alloy
Constantan
Chromonickel
Solid insulators	From 10 (to the power of 6) and above	10 (to the power of minus 6)
	10(to the power of 19)	10 (to the power of minus 19)
	10(to the power of 20)	10 (to the power of minus 20)
Liquid insulators	From 10 (to the power of 10) and above	10 (to the power of minus 10)
gaseous	From 10 (to the power of 14) and above	10 (to the power of minus 14)

From the table you can see that the most conductive materials are silver, gold, copper and aluminum. Due to their high cost, silver and gold are used only in high-tech schemes. And copper and aluminum are widely used as conductors.
It is also clear that no absolutely conductive materials, therefore, when calculating, it must always be taken into account that current is lost in the wires and voltage drops.
There is another, rather large and "interesting" group of materials - semiconductors. The conductivity of these materials varies with environmental conditions. Semiconductors begin to conduct current better or, conversely, worse if they are heated / cooled, or illuminated, or bent, or, for example, shocked.

Symbols in electrical circuits.

To fully understand the processes occurring in the circuit, it is necessary to be able to correctly read electrical circuits. To do this, you need to know the conventions. Since 1986, the standard has come into force, which largely removed the discrepancies in the designations that exist between European and Russian GOSTs. Now an electrical circuit from Finland can be read by an electrician from Milan and Moscow, Barcelona and Vladivostok.
IN electrical diagrams There are two types of designations: graphic and alphabetic.
The letter codes of the most common types of elements are presented in table No. 2:
TABLE #2

	Devices	Amplifiers, remote controls, lasers…
	Converters of non-electrical quantities into electrical quantities and vice versa (except for power supplies), sensors	Loudspeakers, microphones, sensitive thermoelectric elements, ionizing radiation detectors, synchros.
	Capacitors.
	Integrated circuits, microassemblies.	Memory devices, logical elements.
	Miscellaneous elements.	Lighting devices, heating elements.
	Dischargers, fuses, protective devices.	Current and voltage protection elements, fuses.
	Generators, power supplies.	Batteries, accumulators, electrochemical and electrothermal sources.
	Indication and signaling devices.	Sound and light alarm devices, indicators.
	Relay contactors, starters.	Current and voltage relays, thermal, time relays, magnetic starters.
	Inductors, chokes.	Chokes for fluorescent lighting.
	Engines.	DC and AC motors.
	Devices, measuring equipment.	Indicating and recording and measuring instruments, counters, clocks.
	Switches and disconnectors in power circuits.	Disconnectors, short circuits, circuit breakers(power)
	Resistors.	Variable resistors, potentiometers, varistors, thermistors.
	Switching devices in control, signaling and measuring circuits.	Switches, switches, switches triggered by various influences.
	Transformers, autotransformers.	Current and voltage transformers, stabilizers.
	Converters of electrical quantities.	Modulators, demodulators, rectifiers, inverters, frequency converters.
	Electrovacuum, semiconductor devices.	Electronic tubes, diodes, transistors, diodes, thyristors, zener diodes.
	Microwave lines and elements, antennas.	Waveguides, dipoles, antennas.
	Contact connections.	Pins, sockets, collapsible connections, current collectors.
	mechanical devices.	Electromagnetic clutches, brakes, cartridges.
	End devices, filters, limiters.	Modeling lines, quartz filters.

Conditional graphic symbols are presented in tables No. 3 - No. 6. Wires in the diagrams are indicated by straight lines.
One of the main requirements in drawing up diagrams is the ease of their perception. An electrician, when looking at the circuit, must understand how the circuit is arranged and how one or another element of this circuit operates.
TABLE #3. Symbols for contact connections

detachable-
inseparable, collapsible
inseparable, inseparable

The point of contact or connection can be located on any section of the wire from one gap to another.

TABLE #4. Symbols of switches, switches, disconnectors.

	closing	opening
Single pole switch
Single pole disconnector
Three-pole switch
Three-pole disconnector
Three-pole disconnector with automatic return (slang name - "AUTOMATIC")
Single-pole disconnector with automatic reset
Push switch (so-called - "BUTTON")
Extract switch
Switch with return when the button is pressed again (can be found in table or wall lamps)
Single-pole travel switch (also known as "terminal" or "terminal")

The vertical lines crossing the moving contacts indicate that all three contacts close (or open) at the same time from one action.
When considering the diagram, it is necessary to take into account the fact that some circuit elements are drawn in the same way, but their letter designation will be different (for example, a relay contact and a switch).

TABLE No. 5. Designation of contactor relay contacts

	closing	opening
with deceleration when actuated
slow down on return
with deceleration on operation and on return

TABLE No. 6. Semiconductors

zener diode
Thyristor
Photodiode
Light-emitting diode
photoresistor
solar cell
Transistor
Capacitor
Throttle
Resistance

DC electrical machines -

Asynchronous three-phase AC electrical machines -

Depending on the letter designation, these machines will be either a generator or an engine.
When marking electrical circuits comply with the following requirements:

1. Sections of the circuit, separated by the contacts of devices, relay windings, devices, machines and other elements, are labeled differently.
2. Sections of the circuit passing through detachable, collapsible or non-separable contact connections are marked in the same way.
3. In three-phase AC circuits, the phases are marked: “A”, “B”, “C”, in two-phase circuits - “A”, “B”; "B", "C"; "C", "A", and in single-phase - "A"; "IN"; "WITH". Zero is denoted by the letter - "O".
4. Sections of circuits of positive polarity are marked with odd numbers, and negative polarity with even numbers.
5. Next to the symbol of power equipment in the drawings of plans, the equipment number according to the plan (in the numerator) and its power (in the denominator) are indicated with a fraction, and for lamps - the power (in the numerator) and the height of the installation in meters (in the denominator).

It must be understood that all electrical circuits show the state of the elements in original state, i.e. when there is no current in the circuit.

Electrical circuit. Parallel and serial connection.

As mentioned above, we can disconnect the load from the generator, we can connect another load to the generator, or we can connect several consumers at the same time. Depending on the tasks at hand, we can turn on several loads in parallel or in series. In this case, not only the circuit changes, but also the characteristics of the circuit.

At parallel connected, the voltage at each load will be the same, and the operation of one load will not affect the operation of other loads.

In this case, the current in each circuit will be different and will be summed up at the junctions.
Itot = I1+I2+I3+…+In
In this way, the entire load in the apartment is connected, for example, lamps in a chandelier, burners in an electric stove, etc.

At consistent switching on, the voltage is distributed in equal shares between consumers

In this case, the total current will pass through all the loads included in the circuit, and if one of the consumers fails, the entire circuit will stop working. Such schemes are used in New Year's garlands. In addition, when using elements of different power in a series circuit, weak receivers simply burn out.
Utot = U1 + U2 + U3 + ... + Un
Power, for any connection method, is summed up:
Rtot = P1 + P2 + P3 + ... + Pn.

Calculation of the cross section of wires.

The current passing through the wires heats them up. The thinner the conductor, and the greater the current passing through it, the stronger the heating. When heated, the insulation of the wire melts, which can lead to a short circuit and a fire. The calculation of the current in the network is not complicated. To do this, you need to divide the power of the device in watts by the voltage: I= P/ U.
All materials have acceptable conductivity. This means that they can pass such a current through each square millimeter (i.e. section) without much loss and heating (see table No. 7).

TABLE No. 7

cross section S(sq.mm.)	Permissible current I
		aluminum

Now, knowing the current, we can easily select the required wire section from the table and, if necessary, calculate the wire diameter using a simple formula: D \u003d V S / n x 2
You can go to the store for the wire.

As an example, we calculate the thickness of the wires for connecting a household stove: From the passport or from the plate on the back of the unit, we find out the power of the stove. Let's say the power (P ) is equal to 11 kW (11,000 watts). Dividing the power by the mains voltage (in most regions of Russia it is 220 Volts), we get the current that the stove will consume:I = P / U =11000/220=50A. If copper wires are used, then the wire cross sectionS must be at least 10 sq. mm.(see table).
I hope the reader will not be offended by me for reminding him that the cross section of a conductor and its diameter are not the same thing. The cross section of the wire is P(pi) timesr squared (n X r X r). Wire diameter can be calculated by taking the square root of the wire gauge divided by P and multiplying the resulting value by two. Realizing that many of us have already forgotten our school constants, let me remind you that Pi is equal to 3,14 , and the diameter is two radii. Those. the thickness of the wire we need will be D \u003d 2 X V 10 / 3.14 \u003d 2.01 mm.

Magnetic properties of electric current.

It has long been noticed that when current passes through conductors, a magnetic field arises that can act on magnetic materials. From a school course in physics, we may remember that opposite poles of magnets attract, and the same poles repel. This circumstance should be taken into account when laying wiring. Two wires carrying current in the same direction will attract each other, and vice versa.
If the wire is twisted into a coil, then, when an electric current is passed through it, the magnetic properties of the conductor will manifest themselves even more strongly. And if you also insert a core into the coil, then we get a powerful magnet.
At the end of the century before last, the American Morse invented a device that made it possible to transmit information over long distances without the help of messengers. This device is based on the ability of the current to excite a magnetic field around the coil. By supplying power to the coil from a current source, a magnetic field arises in it, attracting a moving contact, which closes the circuit of another similar coil, and so on. Thus, being at a considerable distance from the subscriber, it is possible to transmit encoded signals without any problems. This invention has been widely used, both in communications and in everyday life and industry.
The described device has long been outdated and is almost never used in practice. It was replaced by powerful Information Systems, but basically they all continue to work on the same principle.

The power of any motor is disproportionately higher than the power of the relay coil. Therefore, the wires to the main load are thicker than to the control devices.
Let us introduce the concept of power circuits and control circuits. Power circuits include all parts of the circuit leading to the load current (wires, contacts, measuring and control devices). They are highlighted in color on the diagram.

All wires and equipment for control, monitoring and signaling are related to control circuits. They are shown separately in the diagram. It happens that the load is not very large or not particularly pronounced. In such cases, the circuits are conditionally divided according to the strength of the current in them. If the current exceeds 5 amperes - the power circuit.

Relay. Contactors.

The most important element of the already mentioned Morse apparatus is RELAY.
This device is interesting in that the coil can be fed relatively weak signal, which is converted into a magnetic field and closes another, more powerful, contact, or group of contacts. Some of them may not close, but, on the contrary, open. This is also needed for different purposes. In the drawings and diagrams, this is depicted as follows:

And it reads like this: when power is applied to the relay coil - K, the contacts: K1, K2, K3, and K4 close, and the contacts: K5, K6, K7 and K8 open. It is important to remember that the diagrams show only those contacts that will be used, despite the fact that the relay may have more contacts.
On circuit diagrams ah, it is precisely the principle of building a network and its operation that is shown, so the contacts and the relay coil are not drawn together. In systems where there are many functional devices, the main difficulty is how to correctly find the contacts corresponding to the coils. But with the acquisition of experience, this problem is solved more easily.
As we have said, current and voltage are different matters. The current itself is very strong and it takes a lot of effort to turn it off. When the circuit is disconnected (electricians say - switching) there is a large arc that can ignite the material.
At a current strength of I = 5A, an arc 2 cm long occurs. At high currents, the dimensions of the arc reach monstrous sizes. You have to take special measures not to melt the contact material. One of these measures is ""arc chambers"".
These devices are placed at the contacts on the power relays. In addition, the contacts have a different shape than the relay, which allows you to split it in half even before the arc occurs. Such a relay is called contactor. Some electricians have dubbed them starters. This is wrong, but it accurately conveys the essence of the work of contactors.
All electrical appliances are manufactured in various sizes. Each size indicates the ability to withstand currents of a certain strength, therefore, when installing equipment, it is necessary to ensure that the size of the switching device matches the load current (table No. 8).

TABLE No. 8

Value, (conditional number of standard size)	Rated current	Rated power

Generator. Engine.

The magnetic properties of the current are also interesting in that they are reversible. If with the help of electricity you can get a magnetic field, then you can and vice versa. After not very long studies (only about 50 years), it was found that If the conductor is moved in a magnetic field, then an electric current begins to flow through the conductor . This discovery helped humanity overcome the problem of energy storage and storage. Now we have an electric generator in service. The simplest generator is not complicated. A coil of wire rotates in the field of a magnet (or vice versa) and a current flows through it. It remains only to close the circuit to the load.
Of course, the proposed model is greatly simplified, but in principle the generator differs from this model not so much. Instead of one turn, kilometers of wire are taken (this is called winding). Instead of permanent magnets, electromagnets are used (this is called excitement). The biggest problem in generators is how to take the current. The device for the selection of generated energy is collector.
When installing electrical machines, it is necessary to monitor the integrity of the brush contacts and their tightness to the collector plates. When replacing brushes, they will have to be ground.
There is another interesting feature. If you do not take current from the generator, but, on the contrary, apply it to its windings, then the generator will turn into an engine. This means that electric machines are completely reversible. That is, without changing the design and circuit, we can use electrical machines, both as a generator and as a source of mechanical energy. For example, an electric train consumes electricity when moving uphill, and gives it to the network when moving downhill. There are many such examples.

Measuring instruments.

One of the most dangerous factors associated with the operation of electricity is that the presence of current in the circuit can only be determined by being under its influence, i.e. touching him. Up to this point, the electric current does not betray its presence. In connection with this behavior, there is an urgent need to detect and measure it. Knowing the magnetic nature of electricity, we can not only determine the presence / absence of current, but also measure it.
There are many instruments for measuring electrical quantities. Many of them have a magnet winding. The current flowing through the winding excites a magnetic field and deflects the arrow of the device. The stronger the current, the more the arrow deviates. For greater measurement accuracy, a mirror scale is used so that the view of the arrow is perpendicular to the measuring panel.
Used to measure current ammeter. It is included in the circuit in series. To measure the current, the value of which is greater than the nominal, the sensitivity of the device is reduced shunt(strong resistance).

Voltage measure voltmeter, it is connected in parallel to the circuit.
A combined instrument for measuring both current and voltage is called avometer.
Used to measure resistance ohmmeter or megger. These devices often ring the circuit to find an open or to verify its integrity.
Measuring instruments must be periodically tested. At large enterprises, measuring laboratories are created specifically for these purposes. After testing the device, the laboratory puts its stamp on its front side. The presence of a brand indicates that the device is operational, has an acceptable measurement accuracy (error) and, subject to correct operation, until the next verification, his testimony can be trusted.
The electricity meter is also a measuring instrument, which also has the function of accounting for the electricity used. The principle of operation of the counter is extremely simple, as is its device. It has a conventional electric motor with a gearbox connected to wheels with numbers. As the current in the circuit increases, the motor spins faster, and the numbers themselves move faster.
In everyday life, we do not use professional measuring equipment, but due to the absence of the need for very accurate measurement it's not that significant.

Methods for obtaining contact compounds.

It would seem that there is nothing easier than connecting two wires to each other - twisted and that's it. But, as experience confirms, the lion's share of losses in the circuit falls precisely at the joints (contacts). The fact is that atmospheric air contains OXYGEN, which is the most powerful oxidizing agent found in nature. Any substance, coming into contact with it, undergoes oxidation, being covered first with the thinnest, and over time, with an increasingly thick oxide film, which has a very high resistivity. In addition, problems arise when connecting conductors consisting of different materials. Such a connection, as is known, is either a galvanic pair (which oxidizes even faster) or a bimetallic pair (which changes its configuration with a temperature drop). Several methods of reliable connections have been developed.
Welding connect iron wires when installing grounding and lightning protection equipment. Welding work is done by a qualified welder and electricians prepare the wires.
Copper and aluminum conductors are connected by soldering.
Before soldering, the wires are stripped of insulation up to a length of 35 mm, cleaned to a metallic sheen and treated with flux in order to degrease and for better adhesion of the solder. The components of fluxes can always be found at retail outlets and pharmacies in the right quantities. The most common fluxes are shown in table No. 9.
TABLE No. 9 Compositions of fluxes.

Flux grade	Application area	Chemical composition %
	Soldering conductive parts made of copper, brass and bronze.	Rosin-30, Ethyl alcohol-70.
	Soldering of conductor products made of copper and its alloys, aluminum, constantan, manganin, silver.	Vaseline-63, Triethanolamine-6.5, Salicylic acid-6.3, Ethyl alcohol-24.2.
	Soldering of products made of aluminum and its alloys with zinc and aluminum solders.	Sodium fluoride-8, Lithium chloride-36, Chloride zinc-16, Potassium chloride-40.
Aqueous solution of zinc chloride	Soldering of steel, copper and its alloys.	Chloride zinc-40, Water-60.
	Soldering aluminum wires with copper.	Cadmium fluoroborate-10, Ammonium fluoroborate-8, Triethanolamine-82.

For soldering aluminum single-wire conductors 2.5-10 sq. mm. use a soldering iron. The twisting of the cores is performed by double twisting with a groove.


When soldering, the wires are heated until the solder begins to melt. Rubbing the groove with a solder stick, tin the strands and fill the groove with solder, first on one side and then on the other. For soldering aluminum conductors of large sections, a gas burner is used.
Single and stranded copper conductors are soldered with a tinned strand without a groove in a bath of molten solder.
Table No. 10 shows the melting and soldering temperatures of some types of solders and their scope.

TABLE No. 10

	Melting temperature	Soldering temperature	Application area
			Tinning and soldering the ends of aluminum wires.
			Soldering connections, splicing aluminum wires round and rectangular section when winding transformers.
			Soldering by pouring aluminum wires of large cross section.
			Soldering of aluminum and its alloys.
			Soldering and tinning of conductive parts made of copper and its alloys.
			Tinning, soldering of copper and its alloys.
			Soldering parts made of copper and its alloys.
			Soldering semiconductor devices.
			Soldering fuses.
POSSu 40-05			Soldering of collectors and sections of electrical machines, devices.

The connection of aluminum conductors with copper conductors is carried out in the same way as the connection of two aluminum conductors, while the aluminum conductor is first tinned with “A” solder, and then with POSSU solder. After cooling, the place of soldering is isolated.
Lately more and more often, connecting fittings are used, where the wires are connected by bolts in special connecting sections.

grounding .

From long work materials "get tired" and wear out. In case of oversight, it may happen that some conductive part falls off and falls on the body of the unit. We already know that the voltage in the network is due to the potential difference. On the ground, usually, the potential is zero, and if one of the wires falls on the case, then the voltage between the ground and the case will be equal to the mains voltage. Touching the body of the unit, in this case, is deadly.
A person is also a conductor and can pass current through himself from the body to the ground or to the floor. In this case, a person is connected to the network in series and, accordingly, the entire load current from the network will go through the person. Even if the network load is small, it still threatens with significant troubles. The resistance of the average person is approximately 3,000 ohms. A current calculation made according to Ohm's law will show that a current will flow through a person I \u003d U / R \u003d 220/3000 \u003d 0.07 A. It would seem a little, but it can kill.
To avoid this, do grounding. Those. deliberately connect the housings of electrical devices to earth in order to cause a short circuit in the event of a breakdown to the housing. In this case, the protection is activated and turns off the faulty unit.
Earthing switches they are buried in the ground, grounding conductors are attached to them by welding, which are bolted to all units whose housings may be energized.
In addition, as a protective measure, nulling. Those. zero is connected to the body. The principle of operation of protection is similar to grounding. The only difference is that grounding depends on the nature of the soil, its moisture content, the depth of the ground electrodes, the state of many connections, etc. and so on. And zeroing directly connects the body of the unit to the current source.
The rules for the installation of electrical installations say that with a zeroing device, it is not necessary to ground the electrical installation.
grounding conductor is a metallic conductor or group of conductors in direct contact with earth. There are the following types of grounding conductors:

1. in-depth made of strip or round steel and laid horizontally on the bottom of building pits along the perimeter of their foundations;
2. Horizontal made of round or strip steel and laid in a trench;
3. vertical- from steel rods vertically pressed into the ground.

For ground electrodes, round steel with a diameter of 10 - 16 mm, strip steel with a cross section of 40x4 mm, pieces of angle steel 50x50x5 mm are used.
Length of vertical screwed-in and pressed-in earth electrodes - 4.5 - 5 m; hammered - 2.5 - 3 m.
In industrial premises with electrical installations with voltage up to 1 kV, grounding lines with a cross section of at least 100 square meters are used. mm, and with a voltage above 1 kV - at least 120 kV. mm
The smallest allowable dimensions of steel grounding conductors (in mm) are shown in table No. 11

TABLE No. 11

The smallest allowable dimensions of copper and aluminum grounding and neutral conductors (in mm) are given in table No. 12

TABLE No. 12

Above the bottom of the trench, vertical ground electrodes should protrude by 0.1 - 0.2 m for the convenience of welding connecting horizontal rods to them (round steel is more resistant to corrosion than strip steel). Horizontal ground electrodes are laid in trenches with a depth of 0.6 - 0.7 m from the level of the planning mark of the earth.
At the points of entry of conductors into the building, identification marks of the grounding conductor are installed. Grounding conductors and grounding conductors located in the ground are not painted. If the soil contains impurities that cause increased corrosion, earth electrodes with an increased cross section are used, in particular, round steel with a diameter of 16 mm, galvanized or copper-plated earth electrodes, or electrical protection of the earth electrodes against corrosion is carried out.
Grounding conductors are laid horizontally, vertically or parallel to sloping building structures. In dry rooms, grounding conductors are laid directly on concrete and brick bases with strips fastened with dowels, and in damp and especially damp rooms, as well as in rooms with an aggressive atmosphere - on linings or supports (holders) at a distance of at least 10 mm from the base.
Conductors are fixed at distances of 600 - 1,000 mm on straight sections, 100 mm at turns from the tops of corners, 100 mm from branch points, 400 - 600 mm from the floor level of the premises and at least 50 mm from the lower surface of the removable ceilings of the channels.
Openly laid grounding and neutral protective conductors have a distinctive color - a yellow strip along the conductor is painted over a green background.
It is the responsibility of electricians to periodically check the condition of the ground. To do this, the ground resistance is measured with a megger. PUE. The following resistance values ​​of grounding devices in electrical installations are regulated (Table No. 13).

TABLE No. 13

Grounding devices (grounding and grounding) at electrical installations are performed in all cases if the AC voltage is equal to or higher than 380 V, and the DC voltage is higher than or equal to 440 V;
At AC voltage from 42 V to 380 Volts and from 110 V to 440 Volts DC, grounding is carried out in rooms with increased danger, as well as in especially dangerous and outdoor installations. Grounding and grounding in explosive installations is performed at any voltage.
If the grounding characteristics do not meet acceptable standards, work is carried out to restore the grounding.

step voltage.

In the event of a wire breakage and its contact with the ground or the body of the unit, the voltage evenly “spreads” over the surface. At the point where the earth wire touches, it is equal to the mains voltage. But the farther from the center of contact, the greater the voltage drop.
However, with a voltage between potentials of thousands and tens of thousands of volts, even a few meters from the point where the ground wire touches, the voltage will still be dangerous to humans. When a person enters this zone, a current will flow through the human body (along the circuit: earth - foot - knee - groin - another knee - another foot - earth). It is possible, with the help of Ohm's law, to quickly calculate what kind of current will flow, and imagine the consequences. Since the tension occurs, in fact, between the legs of a person, it has received the name - step voltage.
You should not tempt fate when you see a wire hanging from a pole. Measures must be taken for a safe evacuation. And the measures are:
First, do not move in a big step. It is necessary with shuffling steps, without taking your feet off the ground, to move away from the place of contact.
Secondly, you can not fall and crawl!
And, thirdly, before the arrival of the emergency team, it is necessary to limit the access of people to the danger zone.

Three-phase current.

Above, we figured out how a generator and a DC motor work. But these motors have a number of disadvantages that hinder their use in industrial electrical engineering. AC machines have become more widespread. The current removal device in them is a ring, which is easier to manufacture and maintain. Alternating current is no worse than direct current, and in some respects surpasses it. Direct current always flows in the same direction at a constant value. Alternating current changes direction or magnitude. Its main characteristic is the frequency, measured in Hertz. Frequency indicates how many times per second the current changes direction or amplitude. In the European standard, the industrial frequency is f=50 Hertz, in the US standard, f=60 Hertz.
The principle of operation of motors and alternators is the same as that of DC machines.
AC motors have the problem of orienting the direction of rotation. It is necessary either to shift the direction of the current with additional windings, or to use special starting devices. The use of three-phase current solved this problem. The essence of his "device" is that three single-phase systems are connected into one - three-phase. Three wires supply current with a slight delay from each other. These three wires are always called "A", "B" and "C". The current flows in the following way. In phase "A" to the load and from it returns in phase "B", from phase "B" to phase "C", and from phase "C" to "A".
There are two three-phase current systems: three-wire and four-wire. We have already described the first. And in the second there is a fourth neutral wire. In such a system, current is supplied in phases, and removed in zero. This system proved to be so convenient that it is now used everywhere. It is convenient, including the fact that you do not need to redo something if you need to include only one or two wires in the load. Just connect / disconnect and that's it.
The voltage between the phases is called linear (Ul) and is equal to the voltage in the line. The voltage between the phase (Uf) and neutral wire is called phase and is calculated by the formula: Uf \u003d Ul / V3; Uph \u003d Ul / 1.73.
Each electrician has made these calculations for a long time and knows by heart the standard series of voltages (table No. 14).

TABLE No. 14

When included in three-phase network single-phase loads, it is necessary to monitor the uniformity of the connection. Otherwise, it will turn out that one wire will be heavily overloaded, while the other two will remain idle.
All three-phase electrical machines have three pairs of poles and orient the direction of rotation by connecting the phases. At the same time, to change the direction of rotation (electricians say - REVERSE), it is enough to swap only two phases, any.
Likewise with generators.

Inclusion in the "triangle" and "star".

There are three schemes for connecting a three-phase load to the network. In particular, on the cases of electric motors there is a contact box with winding leads. The marking in the terminal boxes of electrical machines is as follows:
the beginning of the windings C1, C2 and C3, the ends, respectively, C4, C5 and C6 (leftmost figure).

A similar marking is also attached to transformers.
"triangle" connection shown in the middle picture. With such a connection, the entire current from phase to phase passes through one load winding and, in this case, the consumer operates at full power. The figure on the far right shows the connections in the terminal box.
star connection can "do" without zero. With this connection, the linear current, passing through two windings, is divided in half and, accordingly, the consumer works at half strength.

When connected ""in a star"" with a neutral wire, only phase voltage is supplied to each load winding: Uph = Ul / V3. The power of the consumer is less on V3.

Electric cars from repair.

A big problem is the old engines that have come out of repair. Such machines, as a rule, do not have plates and terminal outputs. The wires stick out of the cases, and look like noodles from a meat grinder. And if you connect them incorrectly, then at best, the engine will overheat, and at worst, it will burn out.
This happens because one of the three incorrectly connected windings will try to turn the motor rotor in the direction opposite to the rotation created by the other two windings.
To prevent this from happening, it is necessary to find the ends of the windings of the same name. To do this, with the help of a tester, all the windings are “ringed”, simultaneously checking their integrity (the absence of a break and a breakdown on the case). Finding the ends of the windings, they are marked. The chain is assembled as follows. We attach the proposed beginning of the second winding to the intended end of the first winding, connect the end of the second to the beginning of the third, and take the readings of the ohmmeter from the remaining ends.
We enter the resistance value in the table.

Then we disassemble the circuit, change the end and the beginning of the first winding in places and assemble it again. Like last time, the measurement results are entered in the table.
Then we repeat the operation again, swapping the ends of the second winding
We repeat these actions as many times as there are possible switching schemes. The main thing is to accurately and accurately take readings from the device. For accuracy, the entire measurement cycle should be repeated twice. After filling in the table, we compare the measurement results.
The diagram will be correct. with the lowest measured resistance.

Turning on a three-phase motor in single-phase network.

There is a need when a three-phase motor must be plugged into a regular household outlet (single-phase network). To do this, by the method of phase shift using a capacitor, a third phase is forcibly created.

The figure shows the connection of the motor according to the "delta" and "star" scheme. “Zero” is connected to one output, to the second phase, a phase is also connected to the third output, but through a capacitor. To rotate the motor shaft in the desired direction, a starting capacitor is used, which is connected to the network in parallel with the working one.
At a mains voltage of 220 V and a frequency of 50 Hz, the capacitance of the working capacitor in μF is calculated by the formula, Srab \u003d 66 Rnom, Where rnom is the rated motor power in kW.
The capacity of the starting capacitor is calculated by the formula, Descent \u003d 2 Srab \u003d 132 Rnom.
To start a not very powerful engine (up to 300 W), a starting capacitor may not be needed.

Magnetic switch.

Connecting the motor to the network using a conventional switch provides a limited possibility of regulation.
In addition, in the event of an emergency power outage (for example, fuses blow), the machine stops working, but after the network is repaired, the engine starts without a human command. This may lead to an accident.
The need to protect against the disappearance of current in the network (electricians say ZERO PROTECTION) led to the invention magnetic starter. In principle, this is a circuit using the relay already described by us.
To turn on the machine, use the relay contacts "TO" and button S1.
Push button relay coil circuit "TO" receives power and the relay contacts K1 and K2 close. The motor is powered and running. But, releasing the button, the circuit stops working. Therefore, one of the relay contacts "TO" use for shunting buttons.
Now, after opening the contact of the button, the relay does not lose power, but continues to hold its contacts in the closed position. And to turn off the circuit, use the S2 button.
Right assembled circuit after turning off the network, it will not turn on until the person gives a command to do so.

Mounting and circuit diagrams.

In the previous paragraph, we drew a diagram of a magnetic starter. This scheme is fundamental. It shows how the device works. It includes elements used in this device(scheme). Although a relay or contactor may have more contacts, only those that will be used are drawn. Wires are drawn, if possible, in straight lines and not in a natural way.
Along with circuit diagrams, wiring diagrams are used. Their task is to show how the elements of the electrical network or device should be mounted. If the relay has several contacts, then all contacts are indicated. On the drawing, they are placed as they will be after installation, the wire connection points are drawn where they really should be attached, etc. Below, the left figure shows an example of a circuit diagram, and the right figure shows a wiring diagram of the same device.

Power circuits. Control circuits.

With knowledge, we can quickly calculate the required wire cross-section. The motor power is disproportionately higher than the power of the relay coil. Therefore, the wires leading to the main load are always thicker than the wires leading to the control devices.
Let us introduce the concept of power circuits and control circuits.
Power circuits include all parts that conduct current to the load (wires, contacts, measuring and control devices). In the diagram, they are marked with bold lines. All wires and equipment for control, monitoring and signaling are related to control circuits. They are marked with dotted lines in the diagram.

How to assemble electrical circuits.

One of the difficulties in the work of an electrician is understanding how the circuit elements interact with each other. Must be able to read, understand and assemble diagrams.
When assembling circuits, follow the easy rules:
1. Assembly of the circuit should be carried out in one direction. For example: we assemble the circuit clockwise.
2. When working with complex, branched circuits, it is convenient to break it into its component parts.
3. If the circuit has a lot of connectors, contacts, connections, it is convenient to break the circuit into sections. For example, first we assemble the circuit from a phase to a consumer, then we assemble it from a consumer to another phase, and so on.
4. Assembly of the circuit should start from the phase.
5. Each time you make a connection, ask yourself the question: What will happen if the voltage is applied now?
In any case, after assembly, we should get a closed circuit: For example, the socket phase - the switch contact connector - the consumer - the “zero” of the socket.
Example: Let's try to assemble the most common scheme in everyday life - connect a home chandelier of three shades. We use a two-button switch.
To begin with, let's decide for ourselves how the chandelier should work? When you turn on one key of the switch, one lamp in the chandelier should light up, when you turn on the second key, the other two light up.
In the diagram, you can see that both the chandelier and the switch go to three wires, while only a couple of wires go from the network.
To begin with, using an indicator screwdriver, we find the phase and connect it to the switch ( zero can not be interrupted). The fact that two wires go from the phase to the switch should not confuse us. We choose the place of connection of the wires ourselves. We screw the wire to the common rail of the switch. Two wires will go from the switch and, accordingly, two circuits will be mounted. One of these wires is connected to the lamp socket. We derive the second wire from the cartridge, and connect it to zero. The circuit of one lamp is assembled. Now, if you turn on the switch key, the lamp will light up.
We connect the second wire coming from the switch to the cartridge of another lamp and, just as in the first case, we connect the wire from the cartridge to zero. When the switch keys are alternately turned on, different lamps will light up.
It remains to connect the third light bulb. We connect it in parallel to one of the finished circuits, i.e. we remove the wires from the cartridge of the connected lamp and connect it to the cartridge of the last light source.
It can be seen from the diagram that one of the wires in the chandelier is common. It usually differs from the other two wires in color. As a rule, it is not difficult, without seeing the wires hidden under the plaster, to connect the chandelier correctly.
If all the wires are of the same color, then we proceed as follows: we connect one of the wires to the phase, and we call the others one by one with an indicator screwdriver. If the indicator glows differently (in one case it is brighter, and in the other it is dimmer), then we have not chosen a “common” wire. Change the wire and repeat the steps. The indicator should glow equally brightly when both wires are “ringing”.

Schema Protection

The lion's share of the cost of any unit is the price of the engine. Overloading the motor leads to its overheating and subsequent failure. Great attention is paid to the protection of motors from overloads.
We already know that when running, motors draw current. During normal operation (operation without overloads), the motor consumes normal (rated) current, during overload, the motor consumes a current of very large quantities. We can control the operation of motors with devices that respond to changes in current in the circuit, for example, overcurrent relay And thermal relay.
An overcurrent relay (often referred to as a "magnetic release") consists of several turns of very thick wire on a movable core loaded with a spring. The relay is installed in the circuit in series with the load.
The current flows through the winding wire and creates a magnetic field around the core, which tries to move it. Under normal motor operating conditions, the force of the spring holding the core is greater than the magnetic force. But, with an increase in the load on the engine (for example, the hostess put more laundry in the washing machine than the instructions require), the current increases and the magnet “overpowers” ​​the spring, the core shifts and acts on the drive of the NC contact, the network opens.
Overcurrent relay with works with a sharp increase in the load on the electric motor (overload). For example, a short circuit has occurred, the machine shaft is jammed, etc. But there are cases when the overload is insignificant, but it lasts a long time. In such a situation, the engine overheats, the insulation of the wires melts and, in the end, the engine fails (burns out). To prevent the development of the situation according to the described scenario, a thermal relay is used, which is an electromechanical device with bimetallic contacts (plates) that pass electric current through them.
When the current increases above the nominal value, the heating of the plates increases, the plates bend and open their contact in the control circuit, interrupting the current to the consumer.
For the selection of protection equipment, you can use table No. 15.

TABLE No. 15

			I nom of the machine	I magnetic release	I rated thermal relay	S alu. veins

Automation

In life, we often come across devices whose name is combined under the general concept - "automation". And although such systems are developed by very smart designers, they are maintained by simple electricians. You should not be afraid of this term. It only means "WITHOUT HUMAN INVOLVEMENT".
IN automatic systems ah man gives only the initial command to the whole system and sometimes shuts it down for maintenance. The rest of the work for a very long time the system does itself.
If you look closely at modern technology, you can see a large number of automatic systems that manage it, reducing human intervention in this process to a minimum. A certain temperature is automatically maintained in the refrigerator, and a set reception frequency is set on the TV, the street light turns on at dusk and goes out at dawn, the supermarket door opens in front of visitors, and modern washing machines “independently” perform the entire process of washing, rinsing, spinning and drying underwear. Examples can be given endlessly.
At its core, all automation circuits repeat the circuit of a conventional magnetic starter, to one degree or another improving its speed or sensitivity. Instead of the “START” and “STOP” buttons, we insert contacts B1 and B2 into the already known starter circuit, which are triggered by various influences, for example, temperature, and we get the refrigerator automation.


When the temperature rises, the compressor turns on and drives the cooler into the freezer. When the temperature drops to the desired (set) value, another such button will turn off the pump. Switch S1 in this case plays the role of a manual switch to turn off the circuit, for example, during maintenance.
These contacts are called sensors" or " sensitive elements". Sensors have different shape, sensitivity, setting options and purpose. For example, if you reconfigure the refrigerator sensors and connect a heater instead of a compressor, you get a heat maintenance system. And, by connecting the lamps, we get a lighting maintenance system.
There can be infinitely many such variations.
Generally, the purpose of the system is determined by the purpose of the sensors. Therefore, different sensors are used in each individual case. Studying each specific sensing element does not make much sense, as they are constantly being improved and changed. It is more expedient to understand the principle of operation of sensors in general.

Lighting

Depending on the tasks performed, lighting is divided into the following types:

1. Working lighting - provides the necessary illumination in the workplace.
2. Security lighting - installed along the boundaries of protected areas.
3. Emergency lighting - is intended to create conditions for the safe evacuation of people in case of emergency shutdown of working lighting in rooms, passages and stairs, as well as to continue work where this work cannot be stopped.

And what would we do without Ilyich's ordinary light bulb? Previously, at the dawn of electrification, lamps with carbon electrodes shone on us, but they quickly burned out. Later, tungsten filaments began to be used, while air was pumped out of the bulbs of the lamps. Such lamps lasted longer, but were dangerous due to the possibility of rupture of the bulb. An inert gas is pumped inside the bulbs of modern incandescent lamps; such lamps are safer than their predecessors.
Available incandescent lamps with flasks and socles different shapes. All incandescent lamps have a number of advantages, the possession of which guarantees their use even for a long time. We list these advantages:

1. Compactness;
2. Ability to work with both AC and DC.
3. Unaffected by the environment.
4. The same light output throughout the entire service life.

Along with the listed advantages, these lamps have a very short service life (approximately 1000 hours).
Currently, due to the increased light output, tubular halogen incandescent lamps are widely used.
It happens that the lamps burn out unreasonably often and, it would seem, for no reason. This can happen due to sudden voltage surges in the network, with uneven distribution of loads in the phases, as well as for some other reasons. This "disgrace" can be put an end to if you replace the lamp with a more powerful one and include an additional diode in the circuit, which allows you to reduce the voltage in the circuit by half. At the same time, a more powerful lamp will shine in the same way as the previous one, without a diode, but its service life will double, and the electricity consumption, as well as the fee for it, will remain at the same level.

Tubular fluorescent low pressure mercury lamps

according to the spectrum of emitted light are divided into the following types:
LB - white.
LHB - cold white.
LTB - warm white.
LD - day.
LDC - daylight, correct color rendering.
Fluorescent mercury lamps have the following advantages:

1. High light output.
2. Long service life (up to 10,000 hours).
3. Soft light
4. Wide spectral composition.

Along with this, fluorescent lamps have a number of disadvantages, such as:

1. The complexity of the connection scheme.
2. Big sizes.
3. The impossibility of using lamps designed for alternating current in a direct current network.
4. Dependence on the ambient temperature (at temperatures below 10 degrees Celsius, the ignition of the lamps is not guaranteed).
5. Decrease in light output towards the end of service.
6. Pulsations harmful to the human eye (they can only be reduced by the combined use of several lamps and the use of complex switching circuits).

High pressure mercury arc lamps

have a higher light output and are used to illuminate large spaces and areas. The advantages of lamps include:

1. Long service life.
2. Compactness.
3. Resistance to environmental conditions.

The disadvantages of lamps listed below hinder their use for domestic purposes.

1. The spectrum of lamps is dominated by blue-green rays, which leads to incorrect color perception.
2. Lamps work only on alternating current.
3. The lamp can only be turned on through the ballast choke.
4. The lamp stays on for up to 7 minutes when switched on.
5. Re-ignition of the lamp, even after a short-term shutdown, is possible only after it has almost completely cooled down (i.e., after about 10 minutes).
6. The lamps have significant pulsations of the luminous flux (greater than those of fluorescent lamps).

Recently, metal halide (DRI) and metal halide mirror (DRIZ) lamps, which have better color rendering, as well as sodium lamps (DNAT), which emit golden-white light, are increasingly being used.

Electrical wiring.

There are three types of wiring.
open- laid on the surfaces of walls of ceilings and other elements of buildings.
Hidden- laid inside the structural elements of buildings, including under removable panels, floors and ceilings.
outdoor- laid on the outer surfaces of buildings, under canopies, including between buildings (no more than 4 spans of 25 meters, off roads and power lines).
At open method wiring must comply with the following requirements:

• On combustible bases, asbestos sheet with a thickness of at least 3 mm is placed under the wires with a protrusion of the sheet due to the edges of the wire of at least 10 mm.
• Wires with a dividing wall can be fastened with nails with ebonite washers placed under the hat.
• When the wire is turned on an edge (i.e. 90 degrees), a separating film is cut out at a distance of 65 - 70 mm and the core closest to the turn is bent inside the turn.
• When attaching bare wires to insulators, the latter should be installed with the skirt down, regardless of where they are attached. The wires in this case should be out of reach for accidental contact.
• With any method of laying wires, it must be remembered that the wiring lines should only be vertical or horizontal and parallel to the architectural lines of the building (an exception is possible for hidden wiring laid inside structures with a thickness of more than 80 mm).
• Routes for power outlets are located at the height of the outlets (800 or 300 mm from the floor) or in the corner between the partition and the top of the ceiling.
• Descents and ascents to switches and lamps are performed only vertically.

Wiring devices are attached:

• Switches and switches at a height of 1.5 meters from the floor (in schools and preschool institutions 1.8 meters).
• Plug connectors (sockets) at a height of 0.8 - 1 m from the floor (in school and preschool institutions 1.5 meters)
• The distance from grounded devices must be at least 0.5 meters.
• Above-plinth sockets installed at a height of 0.3 meters and below must have a protective device that closes the sockets when the plug is removed.

When connecting electrical installation devices, it must be remembered that zero cannot be broken. Those. only the phase should be suitable for switches and switches, and it should be connected to the fixed parts of the device.
Wires and cables are marked with letters and numbers:
The first letter indicates the core material:
A - aluminum; AM - aluminum-copper; AC - made of aluminum alloy. The absence of letters means that the conductors are copper.
The following letters indicate the type of core insulation:
PP - flat wire; R - rubber; B - polyvinyl chloride; P - polyethylene.
The presence of subsequent letters indicates that we are not dealing with a wire, but with a cable. The letters indicate the material of the cable sheath: A - aluminum; C - lead; N - nairite; P - polyethylene; ST - steel corrugated.
Core insulation has a designation similar to wires.
The fourth letters from the beginning speak about the material of the protective cover: G - without cover; B - armored (steel tape).
The numbers in the designations of wires and cables indicate the following:
The first digit is the number of cores
The second digit is the cross section of the core in square meters. mm.
Third digit - Rated voltage networks.
For example:
AMPPV 2x3-380 - wire with aluminum-copper conductors, flat, in PVC insulation. Two wires with a cross section of 3 square meters. mm. each, rated at 380 volts, or
VVG 3x4-660 - a wire with 3 copper conductors with a cross section of 4 square meters. mm. each in polyvinyl chloride insulation and the same sheath without a protective cover, designed for 660 volts.

Providing first aid to victims of electric shock.

If a person is struck by an electric current, urgent measures must be taken to quickly release the victim from its effects and immediately provide the victim with medical assistance. Even the slightest delay in providing such assistance can lead to death. If it is impossible to turn off the voltage, the victim should be freed from live parts. If a person is injured at a height, before turning off the current, measures are taken to prevent the victim from falling (the person is taken on his hands or pulled under the place of the alleged fall with a tarpaulin, strong fabric, or soft material is placed). To free the victim from live parts at mains voltages up to 1000 volts, dry improvised objects are used, such as a wooden pole, board, clothes, rope or other non-conductive materials. The person providing assistance should use electrical protective equipment (dielectric mat and gloves) and take only the victim’s clothes (provided that the clothes are dry). At a voltage of more than 1000 volts, an insulating rod or tongs must be used to release the victim, while the rescuer must wear dielectric boots and gloves. If the victim is unconscious, but with a stable breathing and pulse, he should be comfortably laid on a flat surface, unbuttoned clothes, brought to consciousness by smelling ammonia and sprinkled with water, provide fresh air and complete rest. Immediately and simultaneously with the provision of first aid, a doctor should be called. If the victim is breathing poorly, infrequently and spasmodically, or breathing is not monitored, CPR (cardiopulmonary resuscitation) should be started immediately. Artificial respiration and chest compressions should be performed continuously until the doctor arrives. The question of the advisability or futility of further CPR is decided ONLY by the doctor. You must be able to perform CPR.

Residual current device (RCD).

Residual current devices designed to protect a person from electric shock in group lines supplying plug sockets. Recommended for installation in power circuits of residential premises, as well as any other premises and objects where people or animals can be. Functionally, an RCD consists of a transformer whose primary windings are connected to the phase (phase) and neutral conductors. A polarized relay is connected to the secondary winding of the transformer. During normal operation of the electrical circuit, the vector sum of the currents through all windings is zero. Accordingly, the voltage at the terminals of the secondary winding is also zero. In the event of a leakage "to earth", the sum of the currents changes and a current appears in the secondary winding, causing the operation of a polarized relay that opens the contact. Once every three months it is recommended to check the operability of the RCD by pressing the "TEST" button. RCDs are divided into low-sensitivity and high-sensitivity. Low sensitivity (leakage currents 100, 300 and 500 mA) to protect circuits that do not have direct contact with people. They work when the insulation of electrical equipment is damaged. Highly sensitive RCDs (leakage currents of 10 and 30 mA) are designed for protection when it is possible for service personnel to touch the equipment. For the comprehensive protection of people, electrical equipment and wiring, in addition, differential circuit breakers are produced that perform the functions of both a residual current device and a circuit breaker.

Current rectification circuits.

In some cases, it becomes necessary to convert alternating current to direct current. If we consider an alternating electric current in the form of a graphic image (for example, on an oscilloscope screen), we will see a sinusoid crossing the ordinate with an oscillation frequency equal to the frequency of the current in the network.

Diodes (diode bridges) are used to rectify alternating current. The diode has one interesting property - to pass current in only one direction (it, as it were, “cuts off” the lower part of the sinusoid). There are the following AC rectification circuits. A half-wave circuit, the output of which is a pulsating current equal to half the mains voltage.

A full-wave circuit formed by a diode bridge of four diodes, at the output of which we will have a constant current of the mains voltage.

A three-half-wave circuit is formed by a bridge consisting of six diodes in a three-phase network. At the output, we will have two phases of direct current with a voltage Uv \u003d Ul x 1.13.

transformers

A transformer is a device that converts alternating current of one magnitude into the same current of another magnitude. The transformation occurs as a result of the transmission of a magnetic signal from one winding of the transformer to another through a metal core. To reduce losses during conversion, the core is assembled with plates made of special ferromagnetic alloys.


The calculation of the transformer is simple and, in essence, is a solution to the ratio, the basic unit of which is the transformation ratio:
K =UP/Uin =WP/WV, Where UP and U V - respectively, the primary and secondary voltage, WP And WV - respectively, the number of turns of the primary and secondary windings.
After analyzing this ratio, you can see that there is no difference in the direction of the transformer. It's just a matter of which winding to take as the primary.
If one of the windings (any) is connected to a current source (in this case it will be primary), then at the output of the secondary winding we will have a higher voltage if the number of its turns is greater than that of the primary winding, or less if the number of its turns is less, than the primary winding.
Often there is a need to change the voltage at the output of the transformer. If there is “not enough” voltage at the output of the transformer, it is necessary to add turns of wire to the secondary winding and, accordingly, vice versa.
The calculation of the additional number of turns of wire is as follows:
First you need to find out what voltage falls on one turn of the winding. To do this, we divide the operating voltage of the transformer by the number of turns of the winding. Suppose a transformer has 1000 turns of wire in the secondary winding and 36 volts at the output (and we need, for example, 40 volts).
U\u003d 36/1000 \u003d 0.036 volts in one turn.
In order to get 40 volts at the output of the transformer, 111 turns of wire must be added to the secondary winding.
40 - 36 / 0.036 = 111 turns,
It should be understood that there is no difference in the calculations of the primary and secondary windings. Just in one case, the windings are added, in the other, they are subtracted.

Applications. Selection and application of protective equipment.

Circuit breakers provide protection for devices against overload or short circuit and are selected based on the characteristics of the wiring, the breaking capacity of the switches, the value of the rated current and the tripping characteristics.
The breaking capacity must correspond to the value of the current at the beginning of the protected section of the circuit. When connected in series, a device with a low short-circuit current value can be used if a circuit breaker is installed closer to the power source with a lower instantaneous breaker cut-off current than subsequent devices.
Rated currents are selected so that their values ​​are as close as possible to the rated or rated currents of the protected circuit. The tripping characteristics are determined taking into account that short-term overloads caused by inrush currents must not cause them to trip. In addition, it should be taken into account that the circuit breakers must have a minimum opening time in the event of a short circuit at the end of the protected circuit.
First of all, it is necessary to determine the maximum and minimum values ​​​​of the short-circuit current (SC). The maximum short circuit current is determined from the condition when the short circuit occurs directly on the contacts of the circuit breaker. The minimum current is determined from the condition that the short circuit occurs in the farthest section of the protected circuit. A short circuit can occur both between zero and phase, and between phases.
For a simplified calculation of the minimum short-circuit current, you should know that the resistance of the conductors as a result of heating increases to 50% of the nominal value, and the voltage of the power supply decreases to 80%. Therefore, for the case of a short circuit between phases, the short circuit current will be:
I = 0,8 U/ (1.5r 2L/ S), where p is the specific resistance of the conductors (for copper - 0.018 ohm sq. mm / m)
for the case of a short circuit between zero and phase:
I =0,8 Uo/(1.5 p(1+m) L/ S), where m is the ratio of the cross-sectional areas of the wires (if the material is the same), or the ratio of the zero and phase resistances. The machine must be selected according to the value of the rated conditional short-circuit current not less than the calculated one.
RCD must be certified in Russia. When choosing an RCD, the connection diagram of the zero working conductor is taken into account. In the TT grounding system, the sensitivity of the RCD is determined by the grounding resistance at the selected safe voltage limit. The sensitivity threshold is determined by the formula:
I= U/ Rm, where U is the limiting safety voltage, Rm is the grounding resistance.
For convenience, you can use the table number number 16

TABLE No. 16

RCD sensitivity mA	Ground resistance Ohm
	Maximum safe voltage 25 V	Maximum safe voltage 50 V

To protect people, RCDs with a sensitivity of 30 or 10 mA are used.

Fused fuse
The current of the fusible link must not be less than the maximum current of the installation, taking into account the duration of its flow: In =Imax/a, where a \u003d 2.5, if T is less than 10 sec. and a = 1.6 if, T is greater than 10 sec. Imax =InK, where K = 5 - 7 times the starting current (from the motor nameplate data)
In - rated current of the electrical installation for a long time flowing through the protective equipment
Imax - maximum current flowing through the equipment for a short time (for example, starting current)
T - the duration of the maximum current flow through the protective equipment (for example, the acceleration time of the motor)
In household electrical installations, the starting current is small; when choosing an insert, you can focus on In.
After calculations, the nearest higher current value is selected from the standard range: 1,2,4,6,10,16,20,25A.
Thermal relay.
It is necessary to choose such a relay so that In of the thermal relay is within the regulation range and is greater than the network current.

TABLE No. 16

	Rated currents	Correction limits
	2,5 3,2 4,5 6,3 8 10.
	5,6 6,8 10 12,5 16 25

Reading electrical diagrams is a necessary skill for representing the operation of electrical networks, nodes, as well as various equipment. Not a single specialist will proceed with the installation of equipment until he has familiarized himself with the regulatory accompanying documents.

Schematic diagrams allow the developer to convey a complete report about the product in a compressed form to the user using conditionally graphical symbols (UGO). To avoid confusion and waste when assembling according to drawings, alphanumeric designations are included in the unified design documentation system (ESKD). All circuit diagrams are developed and applied in full accordance with GOSTs (21.614, 2.722-68, 2.763-68, 2.729-68, 2.755-87). The GOST describes the elements, provides a decoding of the values.

Reading blueprints

The circuit diagram shows all the elements, parts and networks that make up the drawing, electrical and mechanical connections. Reveals the full functionality of the system. All elements of any electrical circuit correspond to the designations positioned in GOST.

A list of documents is attached to the drawing, in which all elements and their parameters are prescribed. Components are specified in alphabetical order, taking into account digital sorting. The list of documents (specification) is indicated on the drawing itself, or is taken out as separate sheets.

The order of studying the drawings

First, the drawing type is determined. According to GOST 2.702-75, each graphic document corresponds to the individual code. All electrical drawings have the letter "E" and the corresponding digital value from 0 to 7. The code "E3" corresponds to the electrical circuit diagram.

Reading the circuit diagram:

• Visually get acquainted with the presented drawing, pay attention to the indicated notes and technical requirements.
• Find on the schematic image all the components indicated in the list of the document;
• Determine the power source of the system and the type of current (single-phase, three-phase);
• Find the main nodes, and determine their power source;
• Familiarize yourself with the elements and devices of protection;
• To study the control method indicated on the document, its tasks and algorithm of actions. Understand the sequence of actions of the device when starting, stopping, short circuit;
• Analyze the operation of each section of the chain, determine the main components, auxiliary elements, study the technical documentation of the listed parts;
• Based on the studied data of the document, draw a conclusion about the processes occurring in each link of the chain shown in the drawing.

Knowing the sequence of actions, alphanumeric symbols, you can read any electrical circuit.

Graphic symbols

The circuit diagram has two varieties - single-line and full. On a single-line drawing, only a power wire with all elements is drawn, if the main network does not differ in individual additions from the standard one. Two or three slashes applied to the wire line indicate a single-phase or three-phase network, respectively. The entire network is drawn in full and generally accepted symbols are affixed in electrical circuits.

Single line electrical circuit diagram, single phase network

Types and meaning of lines

1. Thin and thick solid lines - in the drawings depict the lines of electrical, group communication, lines on the elements of the UGO.
2. Dashed line - indicates the shielding of the wire or devices; denotes a mechanical connection (motor - gearbox).
3. A thin dash-dotted line - is intended to highlight groups of several components that make up parts of a device, or a control system.
4. Dash-dotted with two dots - the line is disconnecting. Shows a breakdown of important elements. Indicates an object remote from the device that is associated with a mechanical or electrical system.

Network connecting lines are shown in full, but according to the standards, they are allowed to be cut off if they interfere with the normal understanding of the circuit. A break is indicated by arrows, next to it are the main parameters and characteristics of electrical circuits.

A bold dot on the lines indicates a connection, a soldering of wires.

Electromechanical components

Schematic representation of electromechanical links and contacts

A - UGO coils of an electromechanical element (magnetic starter, relay)

B - thermal relay

C - device coil with mechanical blocking

D - contacts making (1), breaking (2), switching (3)

E - button

F - designation of a switch (knife switch) on the electrical circuit of the UGO of some measuring instruments. A complete list of these elements is given in GOST 2.729 68 and 2.730 73.

Elements of electrical circuits, devices

Number in the picture	Description	Number in the picture	Description
1	Electricity meter	8	electrolytic capacitor
2	Ammeter	9	Diode
3	Voltmeter	10	Light-emitting diode
4	temperature sensor	11	Diode optocoupler
5	Resistor	12	Image of npn transistor
6	Rheostat (variable resistor)	13	Fuse
7	Capacitor

UGO time relays, buttons, switches, limit switches are often used in the development of electric drive circuits.

Schematic representation of a fuse. When reading an electrical circuit, you should carefully consider all the lines and parameters of the drawing so as not to confuse the purpose of the element. For example, a fuse and a resistor have minor differences. In the diagrams, the power line is depicted passing through the fuse, the resistor is drawn without internal elements.

The image of the circuit breaker in the full diagram

Contact switching device. Serves automatic protection electrical network from accidents, short circuits. Operated mechanically or electrically.

Circuit breaker on a single line diagram

The transformer is a steel core with two windings. There are single and three-phase, step-up and step-down. It is also divided into dry and oil, depending on the method of cooling. Power varies from 0.1 MVA to 630 MVA (in Russia).

UGO transformers

Designation of current transformers on a complete (a) and single-line (c) circuit

Graphic designation of electrical machines (EM)

Electric motors, depending on the type, are capable of more than just consuming energy. When developing industrial systems, motors are used that, when there is no load, generate energy into the network, thereby reducing costs.

A - Three-phase electric motors:

1 - Asynchronous with squirrel-cage rotor

2 - Asynchronous with squirrel-cage rotor, two-speed

3 - Asynchronous with a phase rotor

4 - Synchronous electric motors; generators.

B - DC commutator motors:

1 - with excitation of the winding from a permanent magnet

2 - Electric machine with excitation coil

In conjunction with electric motors, the diagrams show magnetic starters, soft starters, a frequency converter. These devices are used to start electric motors, the smooth operation of the system. The last two elements protect the network from "drawdown" of voltage in the network.

UGO magnetic starter in the diagram

Switches perform the function of switching equipment. Disable and enable certain sections of the network, as needed.

Graphic symbols in the electrical circuits of mechanical switches

Conditional graphic designations of sockets and switches in electrical circuits. They are included in the developed drawings of the electrification of houses, apartments, and industries.

Bell on the electrical diagram according to UGO standards with the indicated size

UGO dimensions in electrical diagrams

On the diagrams, the parameters of the elements included in the drawing are applied. Complete information about the element is written, capacitance if it is a capacitor, nominal voltage, resistance for a resistor. This is done for convenience, so as not to make a mistake during installation, not to waste time calculating and selecting the components of the device.

Sometimes the nominal data does not indicate, in this case the element parameters do not matter, you can select and install a link with a minimum value.

The accepted dimensions of the UGO are prescribed in the GOSTs of the ESKD standard.

Dimensions in ESKD

The sizes of graphic and alphabetic images in the drawing, the thickness of the lines should not differ, but it is permissible to change them proportionally in the drawing. If in the symbols on various GOST electrical circuits there are elements that do not have information about the dimensions, then these components are performed in sizes corresponding to the standard UGO image of the entire circuit.

UGO elements that are part of the main product (device) are allowed to draw smaller size compared to other elements.

Along with the UGO, for a more accurate definition of the name and purpose of the elements, a letter designation is applied to the diagrams. This designation is used for references in text documents and for application to the object. With the help of a letter designation, the name of the element is determined, if this is not clear from the drawing, technical parameters, quantity.

Additionally, one or more numbers are indicated with the letter designation, usually they explain the parameters. An additional letter code indicating the denomination, model, additional data is prescribed in the accompanying documents, or is displayed in the table on the drawing.

To learn how to read electrical circuits, it is not necessary to know all the letter designations by heart, graphic images various elements, it is enough to navigate in the relevant GOST ESKD. The standard includes 64 GOST documents, which reveal the main provisions, rules, requirements and designations.

The main designations used on the diagrams according to the ESKD standard are given in Tables 1 and 2.

Table 1

First letter of the code (mandatory)	Group of element types	Element Type Examples
A	Devices	Amplifiers, telecontrol devices, lasers, masers
B		Loudspeakers, microphones, thermoelectric sensing elements, ionizing radiation detectors, sound pickups, selsyns
C	Capacitors
D		Integrated analog digital circuits, logic elements, memory devices, delay devices
E	Elements are different	Lighting devices, heating devices
F		Discrete flow and voltage protection elements, fuses, arresters
G	Generators, power supplies, quartz oscillators	Batteries, accumulators, electrochemical and electrothermal sources
H	Indicating and signaling devices	Sound and light signaling devices, indicators
K	Relays, contactors, starters	Current and voltage relays, electrothermal relays, time relays, contactors, magnetic starters
L		Chokes for fluorescent lighting
M	Engines	DC and AC motors
P		Indicating, recording and measuring instruments, counters, clocks
Q		Disconnectors, short circuiters, circuit breakers (power)
R	Resistors	Variable resistors, potentiometers, varistors, thermistors
S	Switching devices in control, signaling and measuring circuits	Switches, switches, switches triggered by various influences
T		Current and voltage transformers, stabilizers
U	Converters of electrical quantities into electrical, communication devices	Modulators, demodulators, discriminators, inverters, frequency converters, rectifiers
V		Electronic tubes, diodes, transistors, thyristors, zener diodes
W	Microwave lines and elements, antennas	Waveguides, dipoles, antennas
X	Contact connections	Pins, sockets, collapsible connections, current collectors
Y		Electromagnetic clutches, brakes, cartridges
Z	Terminal devices, filters, limiters	Modeling lines, quartz filters

The main two-letter designations are given in Table 2

First letter of the code (mandatory)	Group of element types	Element Type Examples	Two letter code
A	Device (general designation)
B	Converters of non-electrical quantities into electrical quantities (except generators and power supplies) or vice versa analog or multi-digit converters or sensors for indicating or measuring	Speaker	BA
		Magnetostrictive element	BB
		Detector of ionizing elements	BD
		Selsyn - receiver	BE
		Phone (capsule)	bf
		Selsyn - sensor	BC
		Thermal sensor	BK
		Photocell	BL
		Microphone	BM
		Pressure meter	BP
		Piezo element	BQ
		Speed ​​sensor (tachogenerator)	BR
		Pickup	BS
		Speed ​​sensor	BV
C	Capacitors
D	Integrated circuits, microassemblies	Circuit integrated analog	DA
		Integrated circuit, digital, logic element	DD
		Information storage device	D.S.
		delay device	DT
E	Elements are different	A heating element	EK
		Lighting lamp	EL
		Igniter	ET
F	Surge arresters, fuses, protective devices	Discrete instantaneous current protection element	FA
		Discrete current protection element of inertial action	FP
		fuse	FU
		Discrete voltage protection element, arrester	FV
G	Generators, power supplies	Battery	GB
H	Indicator and signal elements	Sound alarm device	HA
		Symbolic indicator	HG
		Light signaling device	HL
K	Relays, contactors, starters	Current relay	KA
		Relay index	KH
		Relay electrothermal	KK
		Contactor, magnetic starter	KM
		Time relay	KT
		Voltage relay	KV
L	Inductors, chokes	Fluorescent lighting choke	LL
M	Engines	-	-
P	Instruments, measuring equipment	Ammeter	PA
		Pulse counter	PC
		Frequency meter	PF
	Note. PE combination not allowed	Active energy meter	PI
		Reactive Energy Meter	PK
		Ohmmeter	PR
		Recording device	PS
		Clock, action time meter	PT
		Voltmeter	PV
		Wattmeter	PW
Q	Switches and disconnectors in power circuits	Automatic switch	QF
		short circuit	QK
		Disconnector	QS
R	Resistors	Thermistor	RK
		Potentiometer	RP
		Measuring shunt	RS
		Varistor	EN
S	Switching devices in control, signaling and measuring circuits. Note. The designation SF is used for devices without power circuit contacts.	Breaker or switch	SA
		push button switch	SB
		Automatic switch	SF
		Switches triggered by various influences: - from the level	SL
		- from pressure	SP
		- from the position (travel)	SQ
		- on the frequency of rotation	SR
		- on temperature	SK
T	Transformers, autotransformers	Current transformer	TA
		Electromagnetic Stabilizer	TS
		voltage transformer	TV
U	Communication devices. Electrical to electrical converters	Modulator	UB
		Demodulator	UR
		Discriminator	UI
		Frequency converter, inverter, frequency generator, rectifier	USD
V	Electrovacuum devices, semiconductor	diode, zener diode	VD
		Electrovacuum device	VL
		Transistor	VT
		Thyristor	VS
W	Lines and elements of microwave antennas	coupler	W.E.
		short circuit	WK
		Valve	WS
		Transformer, heterogeneity, phase shifter	wt
		Attenuator	WU
		Antenna	WA
X	Contact connections	Current collector, sliding contact	XA
		Pin	XP
		Nest	XS
		Collapsible connection	XT
		High frequency connector	XW
Y	Mechanical devices with electromagnetic drive	Electromagnet	YA
		Brake with electromagnetic drive	YB
		Coupling with electromagnetic drive	YC
		Electromagnetic chuck or plate	YH
Z	Terminal devices Filters. Limiters	limiter	ZL
		Quartz filter	ZQ

Related videos

Electrical devices and their elements in electrical circuits are depicted in the form of conventional graphic symbols, regulated by state standards for unified system design documentation (ESKD).

The standards establish general graphic symbols for electrical, hydraulic, pneumatic and kinematic circuits and special symbols for each type of circuit, including electrical ones.

General purpose symbols

The designations for general use are shown in fig. 4.1…4.8.

Rice. 4.1. Designations of direct and alternating current, methods of connecting windings

On fig. 4.1 shows the following designations:

a - direct current with positive "+" and negative "-" polarities; b - general designation of alternating current; c - general designation of alternating current indicating the number of phases "m", frequency "f" and voltage "U", for example, three-phase alternating current with a frequency of 50 Hz and a voltage of 380 V (only "m" or "f" can be indicated on the image or "U"; d - single-phase winding; d - three-phase winding with a delta, star and zigzag connection.

Rice. 4.2. Designation of electrical communication lines

On fig. 4.2 shows the following designations: a - electrical communication line (wire, cable); b - electrical connection of lines; c - intersection of communication lines; g - a group of electrical communication lines with the number "n"; e - single-line image of a three-wire electrical communication line; e - multi-line image of electrical communication lines indicating all lines (in this example, three).

Note: when depicting electrical communication lines, the thickness of the lines "b" is selected from 0.18 to 1.4 mm, depending on the selected drawing format and the size of the graphic symbols of the elements. In total, it is recommended to use no more than three standard sizes of lines in thickness in the drawing - thin “b”, thickened “2b” and thick “3b” or “4b”.

Rice. 4.3. Image of electrical communication lines

A group of lines with different functional purposes can be combined into a group connection line, depicted by a thick solid line (Fig. 4.3, a) with its branches (Fig. 4.3, b) and intersections (Fig. 4.3, c).

The merging of electrical communication lines into a group one can be carried out at an angle of 90 or 45º (Fig. 4.3, c).

The electrical communication line can be connected to the ground (Fig. 4.3, d) and the body of the electrical device (Fig. 4.3, e).

The screening line is shown by a dashed line (Fig. 4.3, e).

Rice. 4.4. Image of mechanical connection lines

The mechanical connection line is depicted by a dashed line (Fig. 4.4, a), its connections - with a dot (Fig. 4.4, b), intersections - without a dot (Fig. 4.4, c).

At short distance between devices having a mechanical connection, where the mechanical connection line cannot be represented by a dashed line, it is allowed to be represented by two solid parallel lines.

Rice. 4.5. Thread image electrical energy or electrical signal

The flow of electrical energy or an electrical signal is depicted by a line with an arrow in one (Fig. 4.5, a) or in both directions (Fig. 4.5, b).

The direction of movement is also represented by a line with an arrow. Rectilinear movement in one direction (one-way) - according to fig. 4.5, c, in both directions (return) - according to fig. 4.5, d, one-sided discontinuous with dwell - according to fig. 4.5, e, returnable - according to fig. 4.5, e, with one-sided limitation - according to fig. 4.5, g, reciprocating - according to fig. 4.5, h.

Rice. 4.6. Designation of different types of rotational movement

Rotational movement in one direction or the other - according to fig. 4.6, a, return - according to fig. 4.6, discontinuous with dwell - according to fig. according to fig. 4.6, c, one-sided with restriction - according to fig. 4.6, d, rocking - according to fig. 4.6, d.

Rice. 4.7. Designation of elements of the electric drive and control devices

The general designation of the drive - according to fig. 4.7, a, electric machine drive - according to fig. 4.7, b, electromagnetic - according to fig. . 4.7, c, hydraulic - according to fig. . 4.7, d, manual - by

rice. . 4.7, e, with pressing the button - according to fig. . 4.7, e, with the turn of a button or handle - according to fig. . 4.7, g, with a lever - according to fig. . 4.7, h, foot - according to fig. . 4.7, and.

Rice. 4.8. Image of clutches, brakes and locking mechanisms

One-piece coupling - according to fig. 4.8, a, including - according to fig. 4.8, b, disconnecting - according to fig. 4.8, c. The general image of the brake - according to fig. 4.8, d, acting when turned on - according to fig. 4.8, e, when disconnected - according to fig. 4.8, e. The locking mechanism - according to fig. 4.8, g, and with a latch - according to fig. 4.8, h.

Image of electrical machines

Rice. 4.9. Image of electrical machines

When depicting electrical machines, simplified and expanded methods for constructing conditional graphic images are used. With a simplified method, the stator and rotor windings of AC machines are depicted in the form of circles (Fig. 4.9, a ... d), inside which you can indicate the winding connection scheme, for example, the stator windings - into a star, and the rotor - into a triangle (Fig. 4.9, G).

Winding leads are shown in single line and multiline views.

With a single-line image, the outputs are shown in one line, indicating the number of outputs on it, for example, three-phase machines with a squirrel-cage rotor (Fig. 4.9, a) and with a phase rotor (Fig. 4.9, b).

With a multi-line image, all lines are shown in accordance with the number of phases, for example, three-phase ones (Fig. 4.9, c, d). Leads can be placed on either side of the image.

With the expanded method, the stator and phase rotor windings are depicted as chains of semicircles and are arranged taking into account the geometric shift of the axes of the phase windings (Fig. 4.9, e) or without it (Fig. 4.9, g).

It is allowed to use a mixed image, for example, the stator winding - in an expanded way, the rotor winding - in a simplified way (Fig. 4.9, e or f) and vice versa (Fig. 4.9, g).

Rice. 4.10. Image of synchronous machines

In synchronous machines, the windings are also depicted in a simplified (single-line, multi-line) or expanded way, but with an indication of the rotor design.

For example, a synchronous three-phase machine with an excitation winding on a salient-pole rotor (Fig. 4.10, a, b) or on a non-salient-pole (Fig. 4.10, c, d) rotor and a stator winding connected to a star (Fig. 4.10, a, b) or into a triangle (Figure 4.10, c, d).

If there is a short-circuited starting winding (damper cage) on the rotor, it is depicted as in asynchronous machines (Fig. 4.10, e, f).

Rice. 4.11. Picture of DC machines

In DC machines (Fig. 4.11), the armature winding is depicted as a circle with brushes, and the excitation winding is depicted as semicircles, the number of which determines the type of winding.

Two semicircles depict the winding of additional poles (Fig. 4.11, a) three - the winding of series excitation (Fig. 4.11, b) and four - the winding of parallel (Fig. 4.11, d) and independent excitation (Fig. 4.11, e, e) .

The armature and excitation windings are located taking into account (Fig. 4.11, c, e) or without taking into account (Fig. 4.11, b, d, e) the direction of the magnetic field created by the winding.

Picture of transformers

Rice. 4.12. Picture of transformers

When depicting transformers, simplified single-line and multi-line and expanded methods are also used.

With simplified methods, the windings of voltage transformers (Fig. 4.12, a, b) and autotransformers (Fig. 4.12, e) are depicted as circles, and the conclusions - with a single-line method - in one line indicating the number of conclusions, for example, three (Fig. 4.12 , a), with a multilinear - all lines that determine the number of phases, for example, three-phase (Fig. 4.12, b, e).

Inside the circles, a winding connection scheme can be indicated, for example, a star - a triangle (Fig. 4.12, b).

With the expanded method, the windings are depicted as chains of semicircles, the number of which is not set for autotransformers, for transformers - three circles per winding, for example: single-phase transformer (Fig. 4.12, c) and autotransformer (Fig. 4.12, g) with a magnetic circuit.

In current transformers, the primary winding is made in the form of a thickened line marked with dots, and the secondary winding is made in a simplified way in the form of a circle (Fig. 4.12, i) or in an expanded way with two semicircles (Fig. 4.12, k).

Image of inductors, reactors and magnetic amplifiers

Rice. 4.13. Image of inductors, reactors and magnetic amplifiers

Inductors, reactors and magnetic amplifiers are also depicted in simplified and expanded ways, but the most widely used is the expanded method, when their windings are shown as chains of semicircles, for example: an inductor, a reactor without a magnetic circuit (Fig. 4.13, a), with a magnetic circuit

Yes, without a gap (Fig. 4.13, b) and with an air gap (Fig. 4.13, c), a magnetoelectric core (Fig. 4.13, d) and with leads (Fig. 4.13, e).

In the power supply circuits of electric drives, a reactor is used (Fig. 4.13, e). The magnetic amplifier is depicted in a combined way, for example, an amplifier with two magnetic circuits, with two working and one control windings (Fig. 4.13, g), and in a spaced way, in which the working winding (Fig. 4.13, h) and the control winding (Fig. 4.114 , i) are shown separately.

Contact image

Rice. 4.14. Ways to display contacts

Switching devices and contact connections, which include contacts of switches, contactors and relays, have a common designation of contacts: closing (Fig. 4.14, a), opening (Fig. 4.14, c) and switching (Fig. 4.14, e).

Images of contacts are allowed to be depicted in a mirror-rotated position: closing (Fig. 4.14, b), opening (Fig. 4.14, d) and switching (Fig. 4.14, f).

It is allowed to put an unblackened dot at the base of the movable part of the contacts (Fig. 4.14, and ... k).

Contacts of devices with manual return are depicted according to fig. 4.14, g and h.

Image of switches

Rice. 4.15. Image of switches

Switches are depicted with a dot at the base of the moving contact (Fig. 4.15): single-pole - according to fig. 4.15, a, multi-pole in a single-line image - according to fig. 4.15, b and in the multilinear - according to fig. 4.15, c.

The circuit breaker (automatic) is depicted with an indication of the type of release. For example, single-pole maximum current (Figure 4.15, d) or three-pole minimum current (Figure 4.15, e). Depending on the type of switch, the type of action is indicated on its contact, for example, a push-button switch (Fig. 4.15, f, g) and a travel switch (Fig. 4.15, h, i) with make and break contacts, respectively.

Picture of contacts of contactors, relays and command devices

Rice. 4.16. Picture of contacts of contactors, relays and command devices

Power contacts are depicted without arcing (Fig. 4.16, a) and with arcing (Fig. 4.16, b).

Auxiliary contacts of contactors and relay contacts are shown according to the general designation (see fig. 4.14).

The time relay contacts are depicted with an indication of the time delay upon operation (Fig. 4.16, c) and upon return (Fig. 4.16, d) of the relay.

The opening contact of the electrothermal relay is shown in the form of fig. 4.16, e or indicating the locking mechanism and the return button (Fig. 4.16, f), if necessary, emphasize their presence.

Multi-position switches (controllers, universal switches are depicted with an indication of each position, the closure in which is indicated by a dot, for example, a two-position switch without self-return (Fig. 4.16, g), one contact of which is closed in the first position, and the other in the second.

Picture of contact connections

Rice. 4.17. Contact connections

Contact connections are: non-separable (Fig. 4.17, a), collapsible (Fig. 4.17, b), detachable (Fig. 4.17, c), in which a pin (Fig. 4.17, d) and a socket (Fig. 4.17, e) are distinguished ), sliding along the linear (Fig. 4.17, g) and along the annular (Fig. 4.17, h) surfaces. The terminal block is shown in fig. 4.17, e.

Image of the receiving part of electromechanical devices

Rice. 4.18. The receiving part of electromechanical devices

The general designation of the sensing part of electromechanical devices, i.e. coils of electromagnets, the perceiving part of electrothermal relays has the form of a rectangle (Fig. 4.18).

Designations of single-phase windings are carried out according to fig. 4.18, a, and three-phase windings - according to fig. 4.18b.

If necessary, you can specify the type of winding, for example, the current winding - according to

rice. 4.18, c, and the voltage winding - according to fig. 4.18, d, as well as the view of the device, for example, a time relay operating with a delay when triggered - according to fig. 4.18, e and when releasing - according to fig. 4.19, e.

The receiving device of the electrothermal relay is shown in Fig. 4.18, g, electromagnetic clutch - according to fig. 4.18, s.

Picture of fuses, resistors, capacitors

Rice. 4.19. Picture of fuses, resistors, capacitors

The fuse is depicted in fig. 4.19, a. A fixed resistor is depicted without taps and with taps (Fig. 4.19, b, c). The shunt is depicted as fig. 4.19, city

In a variable resistor, a moving contact is indicated by an arrow (Fig. 4.19, e).

Capacitors are shown with constant (Fig. 4.19, g) and variable (Fig. 4.19, h) capacitance. Polar electrolytic capacitors are depicted in fig. 4.19, and, non-polar - according to fig. 4.19, to.

Image of semiconductor devices

Rice. 4.20. Image of semiconductor devices

On fig. 4.20, a - a semiconductor diode is shown, in fig. 4.20, b - zener diode

in fig. 4.20, in - transistor with electrical conductivity p-n-p type, in fig. 4.20, d - transistor with electrical conductivity of the n-p-n type, in fig. 4.20, d - thyristor with cathode control.

A single-phase bridge rectifier circuit with diodes (Gretz bridge) can be depicted in expanded (Fig. 4.20, e) and simplified form (Fig. 4.20, g).

Image of photovoltaic appliances

Rice. 4.21. Image of photovoltaic appliances

On fig. 4.21 shows images of photovoltaic devices with a photoelectric effect: a photoresistor (Fig. 4.21, a), a photodiode (Fig. 4.21, b), a diode photoresistor (Fig. 4.21, c), a p-n-p type phototransistor (Fig. 4.21, d ), diode optocoupler (Fig. 4.21,

e), thyristor optocoupler (Fig. 4.21, f) and resistor optocoupler (Fig. 4.21, g).

Image of light sources and signaling devices

Rice. 4.22. Image of light sources

Light sources in the form of incandescent lighting and signal lamps are shown in fig. 4.22.

When depicting signal lamps, sectors can be blackened (Fig. 4.22, b), because signal lamps have a low power of 10 ... 25 W and, accordingly, a small luminous flux.

Acoustic devices are also used for signaling: an electric bell (Fig. 4.22, c), an electric siren (Fig. 4.22, d), an electric horn (Fig. 4.22, e).

The semiconductor light emitting diode is shown in fig. 4.22, f.

Image of logic elements

Rice. 4.23. Image of logic elements

Binary logical elements are depicted as a main field (Fig. 4.23, a) with direct inputs (on the left in Fig. 4.23, b) and outputs (on the right in the same figure), with inverse inputs and outputs, i.e. function "NOT" (Fig. 4.23, c).

In the upper half of the image field of logical elements, the functions performed by the element are indicated: & - "AND", 1 - "OR", delay (Fig. 4.23, g), amplifier (Fig. 4.23, h), threshold element (Fig. 4.23, i), T-trigger (Fig. 4.23, i).

In combinational logic elements, an additional field is allocated: left (Fig. 4.23, d), right (Fig. 4.23, e) and left and right with the designation of inputs and outputs and indicating the function (Fig. 4.23, f).

General additional remarks

The images shown in fig. 4.1…4.22, according to the standards can be rotated by 90º in any direction (clockwise and counterclockwise), i.e. the given images on vertical lines links can be used for horizontal lines and vice versa.

The sizes of conditional graphic symbols can be increased if necessary, highlight (underline) the special or importance of the corresponding element (device) or in order to place qualifying symbols inside the image or additional information, or reduced to improve compactness.

The dimensions, as well as the formats of the drawing, are selected depending on the volume and complexity of the drawing, the features of the execution (reproduction or microfilm) and the need to perform it by means of electronic computing technology.

2.7. Conditional alphanumeric designations of elements of electrical circuits

Each device, their elements, functional parts on the diagrams is assigned an alphanumeric designation, consisting of a letter designation and a serial number, affixed after the letter designation of the same height as it.

Table 1. Letter codes of elements of electrical circuits

Code	Example	Type of element (device)
A		Devices (amplifiers, etc.)
IN		Converters of non-electric quantities into electrical ones (except for generators and power supplies) and vice versa
BB	Magnetostrictive sensor
BE	Selsyn receiver
Sun	Selsyn sensor
VC	Thermal sensor
BL	Photocell
VR	Pressure meter
BR	Speed ​​sensor (tachogenerator)
VV	Speed ​​sensor
WITH		Capacitors
D		integrated circuits
DA	Analog ICs
DD	Digital microcircuits, logic elements
D.S.	Digital Information Storage Devices
DT	Delay devices
E		Various elements for which no special letter designations are established
EN	A heating element
EL	lighting lamp
F		Surge arresters, fuses, protective devices
FA	Discrete instantaneous current protection element
FP	The same, inertial action
FS	Element of inertial and instantaneous action
FU	Fuse
FV	Discrete voltage protection element, arrester
G		Generators, power supplies
GB	Batteries
H		Indicator and signal devices
ON	Sound alarm device
HL	Light signaling device
K		Relays, contactors, starters
KA	Current relay
KN	Relay index
QC	Relay electrothermal
KM	Contactor, magnetic starter
KR	Relay polarized
CT	Time relay
KV	Voltage relay
M		Engines
R		Instruments and devices, measuring and testing, recording and differentiating devices
RA	Ammeters
RS	Pulse counters
PF	Frequency meter
PJ	Active energy meter
RK	Reactive Energy Meter
PS	Recording device
RT	Watch
PV	Voltmeter
	PW	Wattmeter
Q		Switches and disconnectors in power circuits
QF	Circuit breaker
QK	short circuit
R		Resistors
RK	Thermistor
RP	Potentiometer
RS	Measuring shunt
EN	Varistor
S		Switching devices for control, signaling and measuring circuits
SA	Breaker or switch
SB	push button switch
SL	Level switch
SP	Pressure switch
SQ	Position switch (travel)
SR	Speed ​​triggered switch
ST	Temperature switch
T		transformers
TA	Current transformer
TS	Electromagnetic stabilizer
TV	voltage transformer
U		Converters of electrical quantities into electrical
UR	Modulator, demodulator
UJ	Discriminator (phase sensitive rectifier)
USD	Frequency converter, rectifier, inverter
V		Electrovacuum and semiconductor devices
VD	diode, zener diode
VL	Electrovacuum device
VT	Transistor
VS	Thyristor
X		Contact connections
HA	Sliding contact, current collector
XP	Pin
XS	Nest
HT	Collapsible connection
Y		Electrically driven mechanical devices
YA	Electromagnet
YB	Brake with electromagnetic drive
YC	Coupling with electromagnetic drive
YH	Electromagnetic plates and cartridges
YV	Electromagnetic spool

If the recommendations do not contain the necessary two-letter designations, then, based on the one-letter code, we add the second letter of the Latin alphabet to form a new designation, the meaning of which should be explained in the diagram field, or use the one-letter code, which is preferable.

After the two-letter code and serial number of the element, it is allowed to use an additional letter designation that determines the functional purpose of the element, shown in Table 2.

Table 2. Function letter codes

Letter code	Element (device) function
A	Auxiliary
IN	Direction of travel (forward, backward, up, down, etc.)
WITH	counting
D	differentiating
F	Protective
G	Test
H	Signal
J	Integrating
L	pusher
M	Main
N	Measuring
R	Proportional
Q	State (start, stop, limit)
R	Return, reset
S	memorization, recording
T	Synchronization, bullshit
V	Speed ​​(acceleration, deceleration)
W	Addition
X	Multiplication
Y	analog
Z	Digital

Reading electrical drawings requires certain knowledge, which can be gleaned from normative documents. A kind of "language" of reading are symbols in electrical circuits – a system of signs and symbols, mainly graphic and alphabetic. In addition to them, denominations are sometimes affixed with numbers.

Agree, understanding the standard notation is simply necessary for any home master. This knowledge will help you read the wiring diagram, independently draw up a wiring plan in an apartment or in a private house. We offer to understand all the intricacies of writing project documentation.

The article describes the main types of electrical circuits, as well as a detailed decoding of the basic images, symbols, icons and alphanumeric markers used in drawing up drawings for the electrical network.

Consider the design information from the point of view of an amateur electrician who wants to change the wiring in the house with his own hands or draw up a drawing for connecting the dacha to electrical communications.

First you need to understand what knowledge will be useful and what will not be needed. First step – is an introduction to the species.

A peculiar scheme for connecting electrical installations and protective devices in the electrical panel. In fact, it has nothing to do with professional documentation that accompanies home energy projects.

All information about the types of schemes is set out in the new edition of GOST 2.702-2011, which is called “ESKD. Rules for the implementation of electrical circuits.

This is a duplicate of an earlier document – GOST 2.701-2008, which just talks in detail about the classification of schemes. In total, 10 species are distinguished, but in practice only one may be required. – electric.

In addition to the species classification, there is also a typical one, which subdivides all drawing documents into structural, general, etc., in total 8 points.

The home master will be interested in 3 types of circuits: functional, basic, assembly.

Type #1 - function diagram

The functional diagram does not contain details, it indicates the main blocks and nodes. She gives general idea about the operation of the system. For a private house power supply device, it does not always make sense to draw up such drawings, since they are usually typical.

But when describing a complex electronic device or to equip a workshop, studio or control room with an electrician, they can come in handy.

Switches and sockets – one of the most "demanded" elements in circuits for home use, so they should be remembered first. Read more about the designation of such devices in the drawings and diagrams in.

For various kinds lamps and fixtures are also provided with separate symbols. Conveniently, there are special icons for LED and fluorescent light bulbs.

Table of symbols for light sources. Linear and slotted devices have a rectangular shape, the rest are round or close to it. There is a special symbol for cartridges

Standard images of various types of fixtures are often used to compile wiring diagrams.

If use identical icons, you will have to include additional clarifications, and with typical symbols, you can draw a diagram much faster.

Elements for drawing up circuit diagrams

The basic symbols for circuit diagrams differ little, but besides them there are also special icons for designating all kinds of radio elements: thyristors, resistors, diodes, etc.

Symbols for drawing up or reading circuit diagrams. In addition to graphic symbols, alphanumeric marking can be used if it is necessary to indicate the characteristics of the elements (+)

There are separate designations for radio devices, but when designing a home electrical network, they are usually not required.

Letter designations on wiring diagrams

To give more full information about the device, it is signed with an abbreviated letter designation. Number of letters – 2 or 3. Sometimes the letter designation turns into alphanumeric if you put the serial number of the device next to it.

Table of symbols for schematic elements in international format. A distinctive feature - the letters are set in Latin. By designation, you can determine the device, the number of identical elements, the relationship between them (+)

Along with international standards, there are also Russian standards. They are listed in GOST 7624-55, but this document is declared invalid.

The article does not provide information about all the conventions. Full materials on graphic symbols can be found in GOST 2.709-89, 2.721-74, 2.755-87.

Conclusions and useful video on the topic

From drawing – to circuit diagram:

An example of reading electrical diagrams (part 1):

. There is no need to invent your own symbolism when there is professional system conventions, which is not so difficult to learn.

Have something to add, or have questions about drawing up and reading electrical circuits? You can leave comments on the publication, participate in discussions and share your own drawing development experience. The contact form is in the bottom block.

The ability to read wiring diagrams is an important component, without which it is impossible to become a specialist in the field of electrical work. Every novice electrician must know how sockets, switches, switching devices and even an electricity meter are indicated on the wiring project in accordance with GOST. Next, we will provide readers of the site with symbols in electrical circuits, both graphic and alphabetic.

Graphic

As for the graphic designation of all the elements used in the diagram, we will provide this overview in the form of tables in which the products will be grouped according to their purpose.

In the first table you can see how electrical boxes, boards, cabinets and panels are marked on the wiring diagrams:

The next thing you should know is the symbol for power sockets and switches (including walk-throughs) on single-line diagrams of apartments and private houses:

As for lighting elements, fixtures and lamps according to GOST are indicated as follows:

In more complex schemes where electric motors are used, elements such as:

It is also useful to know how transformers and chokes are graphically indicated on circuit diagrams:

Electrical measuring instruments according to GOST have the following graphic designation in the drawings:

And here, by the way, is a table useful for beginner electricians, which shows how the ground loop looks on the wiring plan, as well as the power line itself:

In addition, on the diagrams you can see a wavy or straight line, “+” and “-”, which indicate the type of current, voltage and pulse shape:

In more complex automation schemes, you may encounter obscure graphic symbols, such as contact connections. Remember how these devices are indicated on the wiring diagrams:

In addition, you should be aware of how radio elements look on projects (diodes, resistors, transistors, etc.):

That's all conditionally graphic designations in electrical circuits of power circuits and lighting. As you yourself have already seen, there are quite a lot of components and you can remember how each is designated only with experience. Therefore, we recommend that you save all these tables for yourself, so that when reading the wiring layout of a house or apartment, you can immediately determine what kind of circuit element is in a certain place.

Interesting video