In accordance with the requirements of the rules for the technical operation of electrical installations (abbreviated as PTE), the power equipment of electric networks, substations and the electric stations themselves must be protected from short-circuit currents and failures of normal operation. As protection equipment, special devices are used, the main element of which is a relay. Actually, that's why they are called so - relay protection devices and electroautomatics (RPA). To date, there are many devices that can as soon as possible prevent an accident on a serviced section of the power grid or, in extreme cases, alert personnel about a violation of the operating mode. In this article we will consider the purpose of relay protection, as well as its types and device.
What is it for?
First of all, we will talk about why you need to use RPA. The fact is that there is such a danger as in a chain. As a result of the short circuit, conductive parts, insulators and the equipment itself are very quickly destroyed, which entails not only the occurrence of an accident, but also an industrial accident.
In addition to a short circuit, gas evolution may occur during the decomposition of oil inside the transformer, etc. In order to detect danger in a timely manner and prevent it, special relays are used that signal (if a malfunction of the equipment does not pose a threat) or instantly turn off the power in the faulty area. This is the main purpose of relay protection and automation.
Basic requirements for protective devices
So, in relation to RPA the following requirements are presented:
- . In the event of an emergency, only that section in which an abnormal operating mode is detected should be turned off. All other electrical equipment should work.
- Sensitivity. Relay protection must respond even to the smallest values \u200b\u200bof the alarm parameters (set by the trip setting).
- Performance. No less important requirement for relay protection, as the faster the relay operates, the less chance of damage to electrical equipment, as well as the occurrence of danger.
- Reliability. Of course, the devices must perform their protective functions in the given operating conditions.
In simple words, the purpose of relay protection and the requirements for it are that the devices must monitor the operation of electrical equipment, respond in a timely manner to changes in the operating mode, instantly disconnect the damaged section of the network and signal personnel about the accident.
Relay classification
When considering this topic, one can not stop at the types of relay protection. The relay classification is as follows:
- Connection method: primary (connected directly to the equipment circuit) and secondary (connected via transformers).
- Variant of execution: electromechanical (the system of movable contacts disengages the circuit) and electronic (disconnection is done using electronics).
- Appointment: measuring (carry out the measurement of voltage, current, temperature and other parameters) and logical (transmit commands to other devices, carry out time delay, etc.).
- Way of action: relay protection of direct action (mechanically connected to the disconnecting device) and indirect effect (control the circuit of the electromagnet, which turns off the power).
As for the types of RPA themselves, there are many of them. Immediately consider what types of relays are and what they are used for.
- Overcurrent protection (MTZ), triggered if the current reaches the setpoint set by the manufacturer.
- Directional overcurrent protection, in addition to the setting, the direction of power is monitored.
- Gas protection (GZ), is used to turn off the power to the transformer as a result of gas evolution.
- Differential, scope - protection of busbars, transformers, as well as generators by comparing the values \u200b\u200bof currents at the input and output. If the difference is greater than the set point, the relay protection is activated.
- Remote (DZ), turns off the power if it detects a decrease in resistance in the circuit, which occurs if a short-circuit current occurs.
- Remote protection with high-frequency interlock, is used to turn off the overhead line when a short circuit is detected.
- Remote with optical channel locking, a more reliable version of the previous type of protection, as the effect of electrical noise on the optical channel is not so significant.
- Logical bus protection (LZS) is also used to detect faults, only in this case on buses and (supply lines extending from substation buses).
- Arc. Purpose - protection of complete switchgears (switchgear) and complete transformer substations (KTP) from fire. The principle of operation is based on the operation of optical sensors as a result of increased illumination, as well as pressure sensors with increasing pressure.
- Differential phase (DFZ). They are used for phase control at two ends of the supply line. If the current exceeds the setpoint, the relay trips.
Separately, I would also like to consider the types of electroautomatics, the purpose of which, in contrast to relay protection, on the contrary, is to turn on the power back. So, in modern relay protection and automation use the following type of automation:
- Automatic reserve input (ABP). Such automation is often used when, as a backup source of power supply.
- Automatic reclosing (AR). Scope - power lines of 1 kV and above, as well as busbars of substations, electric motors and transformers.
- Automatic frequency unloading, which turns off third-party devices when lowering the frequency in the network.
In addition, there are the following types of automation:
So we examined the purpose and scope of relay protection. The last thing I would like to talk about is what the RPA consists of.
Relay Design
The relay protection device is a diagram of the following parts:
- Starting organs -, current, power. Designed to control the operating mode of electrical equipment, as well as detect violations in the circuit.
- Measuring organs - can also be located in the starting organs (current, voltage relays). The main purpose is to start other devices, signaling as a result of detecting an abnormal operating mode, as well as instantly turning off the devices or with a time delay.
- The logical part. Presented by timers as well.
- Executive part. Responsible directly for turning off or on switching devices.
- The transmitting part. It can be used in differential phase protection.
To some this question may seem strange, because the answer is hidden in their name - the position relay is on / off. But if you think that these relays report the current position of the switch, then read on. Because the answer is incorrect.
In order to correctly answer this question, you need to consider the standard wiring diagram of the circuit breaker drive, for example, at 35 kV. Relays RPV (KQC) and RPV (KQT) are highlighted in red.
Fig. 1. Connection diagram of the 35 kV vacuum circuit breaker drive (example)
And here is another circuit, this time for a 110 kV circuit breaker
Fig. 2. Connection diagram for 110 kV SF6 circuit breaker drive (example)
As you can see, the power to the coils of these relays (especially RPO) is supplied along fairly long chains, including other contacts and shutdown electromagnets.
Naturally, in these chains there are block contacts of the switch, but not only they. In the general case, the spring cock control limit switch, the contacts of the gas pressure monitoring relay (blocking stage), etc. can be included here. That is why the RPV and RPO relays cannot signal the current position of the circuit breaker.
What then "show" RPO and RPV?
They indicate the readiness of the drive for operation:
RPO - readiness for the inclusion operation,
RPV - readiness for the shutdown operation.
Let's look at the inclusion circuit on Fig. 1which includes RPO. In addition to the block contact of the Q1 switch and the YAC switching coil, it includes the following elements:
- Switch SA1 in the drive cabinet, which transfers the drive to remote or local (repair) control. To power the RPO input, the switch must be in the remote control position, otherwise the signal will not pass.
- Contacts for monitoring the state of the actuator spring SQM1 and SQM2, which close when the spring is cocked, i.e. when the switch is ready for the closing operation. After each switch-on, the drive spring is discharged, and the SQM contacts open, blocking the passage of the switch-on command until the spring is charged.
- An SQF contact that breaks the closing circuit if there is a parallel circuit breaker command so that there is no multiple switching effect.
If at least one of these elements is in the open state, then the RPO circuit will not assemble, even if the switch is in the off position (Q1 is closed). The combination of all these elements indicates the readiness / unavailability of the switch for the operation of inclusion.
If the circuit breaker is SF6 gas, then the contacts of the SF6 gas pressure switch are added to the on and off circuit, which completely blocks the control during a critical pressure drop. This prevents the circuit breaker from failing due to a failure to extinguish the arc (no SF6 - no extinguishing medium). Such a relay can be seen on Fig. 2 (+ K9)
Also, the relay / RPO or RPV inputs will not be powered when the on and off circuits are broken or the power circuit breaker is turned off. In the event of the disappearance of both RPV and RPO signals, the relay protection and control device gives a warning signal to the duty officer at the substation or in the automatic control system.
Initially, these relays were used precisely to control the integrity of the control circuit of the circuit breaker.
Features of the use of RPV and RPO signals in logic circuits
Signal processing RPO, RPV must be done taking into account the logic of their formation.
For example, the RPO signal may disappear during the spring charging time, especially in the cycle of unsuccessful automatic reclosure (operation O-tapv-VO), when a stable short-circuit occurs again, but the switch-on spring has not yet been charged.
Spring winding time can reach 15 s (VVU-SEShch-P-10) and more, especially at low operating current voltage.
This means that it is necessary to carry out the signaling of the open circuit of the drive (the simultaneous disappearance of RPO and RPV) with a time delay of at least the spring cocking time.
RPV signals are also widely used in protection and automation algorithms. For example, RPV is usually used when starting an automatic reclosure, and RPO when accelerating protection.
Fig. 3. The use of RPV and RPO in the algorithms of MP RPA (for example, BMRZ-152-KL, taken from the site http://mtrele.ru)
In addition, it must be understood that even if all auxiliary contacts are closed, it is still incorrect to judge the position of the switch by RPO and RPV, because in this case the RPO and RPV signals disappear faster than the complete on / off operation.
For example, the RPV signal ( Fig. 1) will disappear at the discrete input of terminal A1 as soon as a command to disconnect the relay contact KCT1 is issued. Those. the switch has not yet had time to open (still on), and the RPV signal has already disappeared (the RPV input is bridged by relay contact KCT1).
The difference here is certainly small (tens of milliseconds), but for systems such as RAS and ACS can be significant. Therefore, for them, the position of the circuit breaker must be "taken" through the "dry" block contacts of the circuit breaker, when powered from the tracer of the corresponding system.
It is the contact block of the circuit breaker with which shows its current position, and the RPV and RPO are the relay monitoring the readiness of the switch for the corresponding operation.
Well, finally, a little observation
Recently, designers and manufacturers of circuit breakers have been trying to take the RPO circuit as far as possible to the switching electromagnet, bypassing the entire complex chain of auxiliary contacts.
On the Fig. 4 shows two schemes for drives of the same type of circuit breakers VVU-SESH-P with a difference of 3 years. On the left you see a diagram from 2010, and on the right a more modern one. Pay attention to the RPO chain - this is what I was talking about. In the first case, you control almost the entire switching circuit, and in the second, only the Q1-YAC section.
The rear axle gearbox includes several nodes, the main of them are the differential and final drive. The main gear is called the mechanism by which the gear ratio of the vehicle’s transmission is increased. So what is a reducer when it was created, what malfunctions can comprehend it, and much more we will tell in this article.
The history of the gearbox
The process of industrial revolution was marked by the transition of wooden parts to metal. Wind and water-propelled thrusters already created efforts that were difficult to withstand for wooden parts. The main factor of the industrial revolution was the creation of more advanced mechanisms, the search for new energy resources.
The advent of the steam engine required very large capacities. Therefore, there was a need for the design of metal gears. By the mid-nineteenth century, manual weaving machines had already begun to recede far into the background and replaced by mechanical ones with three times as much productivity. Energy began to get cheaper, which led to increased machine performance and strengthened their economic advantage. The steam engine was powerful enough to run several textile machines.
Machine tools were placed around the steam engine to increase efficiency. The steam engine freed up its hands on production capabilities, which made it possible to build enterprises near the water, and in those places where there was coal, transport, labor and sales markets. New time has selected optimal gear designs. Those who produced the highest economic effect gained great popularity.
The middle of the 19th century was marked by the appearance of the first serial gearboxes. Well, the appearance in a few years of internal combustion engines and an electric drive, marked the creation of gearboxes with specified parameters. Gear mechanisms transmitted rotational movements from engines with high revolutions and converted their parameters. Even the first examples of electric motors and internal combustion were endowed with too much speed and torque, which, a priori, was not suitable for use in industry. Today, of course, it is difficult to find any vehicle or technological equipment that lacks a gear mechanism. Gearboxes are used in almost all automobiles and technological equipment. As you already understood, gears have passed many years of development.
Design and principle of operation of the gearbox
Despite the fact that many models of rear-wheel drive vehicles as part of the design of the rear axle have gearbox, it looks quite identical, with the rare exception of some samples.Here, we immediately recall the definition of a reducer, which says that this is a device that changes the speed of rotation at the time of transfer of force between the forces between the devices. As a result of a change in the rotation speed, it is likely that its magnitude and direction will change. It is by this principle that the operation of the gearbox used in the construction of the rear axle of almost every vehicle is realized.
The transmission from the drive shaft to the driven shafts, which are located at right angles to it, uses gears, which are gears. Due to the location of the shafts at different angles, the gear teeth are made in a specific shape - these gears are called bevel gears. Bevel gears are used, of course, for rotation, but it is the construction of gears of this type that minimizes the noise emitted during their operation, and this is very important if you are traveling in a compact passenger car, for example.
In order for the gearbox to really reduce the speed of rotation, you need a drive wheel was several times smaller than the driven ones. If the structure is verified correctly, then with a complete rotation of the drive shaft around its axis, the driven shaft will not complete a revolution. Thus, there is a reduction in rotation speed, that is, its decrease. Some types of cars often require a significant reduction in shaft speed, for example, on off-road vehicles that overcome various kinds of mud barriers slowly enough so as not to get stuck in the belly or stuck.
Gear Types
As you already understood, the gearbox is a mechanism that allows you to reduce the speed, while at the same time increasing torque. This is a special unit, which consists of one or more geared gears installed in the housing. It is adapted to change the speed of rotation of the shafts as lowering and increasing. Today, gearboxes are widely used not only in the automotive industry, but also in the construction industry, for lifting goods, manufacturing, coal mining and the oil industry.
Gearboxes are divided into various types. They are usually classified according to several criteria. The most important of these is the type of gear used. And by this principle they are divided into several types: conical, planetary, cylindrical, worm, spiroid, wave and combined.
Helical gears, often in hoisting mechanisms and other areas with often repeated short-term load. They are very durable and their efficiency is quite high.
Bevel gears are more complex in their design than cylindrical gears. The ratio of performance and compactness they stand out very favorably from other types. Bevel gears are widely used in cranes of various designs.
Worm gearboxes are adapted to transmit rotation between the shafts crossing at right angles, by means of the worm and the worm wheel, which is associated with it. A worm is a kind of screw with a trapezoidal thread and close to that. The worm wheel is also called a gear. Its teeth have an arcuate shape. Worm-type gearboxes are widely applicable in metal-cutting machines, trolleybuses and lifts. The main advantage of such gearboxes is noiselessness and smooth operation. The big disadvantage is the increased heat generation, which leads to low efficiency and accelerated wear.
Planetary gearboxescompared with others, they withstand loads perfectly, while possessing a low specific capacity of materials. They are very reliable and at the same time have compact dimensions. They can also be transformed by manufacturers depending on the type of transmission used. Wave reducers were previously used only in rocket science and the defense industry. Wave reducers are very reliable and have great overload capacity, and they also have a long operating mode, they are very compact, smooth and silent in their work.
Spirod gears- These are budget units for the implementation of a small power drive for relatively little money. Combined gearboxes, based on their name, use different types of gears in one housing. For example, worm-bevel and bevel-helical gears. Choosing one or another type of gearboxes, you should be based on the load data - force, mass, moment of inertia, operating time and number of starts in a given time.
Gear malfunctions
Most often, gearbox failures, as an integral part of an automobile transmission, are often associated with the complete exhaustion of the resource of parts that require subsequent replacement. The main causes contributing to the subsequent malfunctions of the rear axle gearbox are:
- worn shaft seals;
Worn liner and differential bearings;
Defective differential elements;
Worn or broken parts of the main pair.
Signs of a broken rear axle gearbox are simply impossible to miss. This is the flow of oil from the gearbox itself, and the characteristic howling sound that comes from this unit when moving. All this immediately gives the cause of the breakdown. And if the leakage of transmission oil is eliminated quite simply by installing a new liner oil seal, then the noise that a broken transmission makes is not easy to remove.
First of all, you should check whether the noise disappears when the machine is coasting. If it disappears, then the cause of the noise is naturally in the main pair of the gearbox. If the noise and hum did not disappear, then most likely the reason is the broken bearings of the shank or differential. Why is it so easy to diagnose such serious malfunctions? We answer. While the car is coasting, the elements of the main pair do not come into contact with the force, therefore they are not able in any way to affect the appearance of strange noise in the car.
Note that often the main pair is subject to increased wear due to low oil levels. When gearbox parts are not sufficiently lubricated, this naturally exposes them to very large frictional and thermal overloads. And the oil level, in turn, decreases sharply due to malfunctions in the oil seal, which becomes unsuitable for operation with a loose tightened shank nut. The next reason leading to the replacement of the rear axle gearbox is the increased transmission load that occurs during prolonged use of the machine with a strong overload. Also, do not exclude the defect of parts from the conveyor that are installed on the rear gear, the cost of which is exorbitantly high.
How is the rear axle gearbox designed?
Consider the device of the rear axle gearbox of the car should be together with other elements that are functionally related to it. It:
- main gear (GP);
Interwheel differential.
Power from the internal combustion engine, more precisely from the gearbox through the pinion gear, is supplied to the driven one. These two gears are called the main gear. GP changes the magnitude and direction of transmission of the moment. Driven gear is interconnected with axles that transmit power from the engine to the wheels. The interwheel differential distributes it between the different axles, allowing them to rotate at different speeds at the moment of changing direction. This principle of constructing the mechanism is implemented on most rear-wheel drive cars. This device is very reliable and works great even in the most difficult road conditions.
Rear axle gear adjustment
Adjusting the rear axle is necessary only in those cases when it really began to bother you with a strange hum that is already heard at speeds from 30 km / h. The main reason for the appearance of characteristic noise in the rear axle gearbox is the constant exposure of the vehicle to heavy overloads or too frequent driving with a trailer or simple mechanical damage. Therefore, do not hesitate to visually diagnose the mechanism.
Oil seals and flanges, bearings, satellites (star-shaped element in the differential) and their axes - all this will need to be removed and inspected, and in case of wear - immediately changed. How all these parts should look in normal working condition, you will learn from the manual for your vehicle. Replacing the gearbox in a domestic car will not be expensive. And if you have a foreign car, then it’s better to study all the price lists and make inquiries at auto parts stores.
Now that all the parts are in good condition (this was revealed by visual diagnostics), you can assemble the gearbox. The first step is the drive gear, then the adjusting washer, flange and spacer sleeve with bearings. Next, tighten the nut with the necessary effort. To do this, we take a special key with a built-in dynamometer, in the absence of one we will have to constantly use the measuring lever. Each millimeter of the lever stroke will need to be accompanied by a steelyard pressure measurement. And this is very troublesome and long, and requires a certain accuracy and caution. The nut should be tightened by 1 Newton, at this time the flange should not move. It must be secured with a special key with spacers that are precisely sized to fit the grooves of the flange. Then mount the driven gear in its place in the differential housing and tighten the bolts.
Now proceed to the direct adjustment of the play. After installing all the parts in their place, tighten all the nuts to a minimum and rotate the driven gear. Next, we check it for a small backlash, swinging the gear from side to side. Remember, there should be a backlash, but not significant! This can be said, a spare place for heating the gearbox. So that nothing bursts when moving.
At the final stage, we check the distance between the bolts holding the nuts that we recently tightened. The nuts must be tightened at the same distance; to do this, use a vernier caliper. After again, check the gear for the presence of play. It is important that he stay that way. That's it, the gearbox adjustment is over.
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