ARRESTERS.

Completed by: Shlemina E.V.

Group: 7203

Faculty: EL

Checked by: Barchenko V.T.

Saint Petersburg

1. Introduction………………………………………………………………………………..3

2. Types of arresters………………………………………………………..3

3. Types of arresters………………………………………………………..4

4. General designation of the arrester……………………………………..10

5. Volt-second characteristic……………………………………...10

6. References……………………………………………………..13

Introduction.

Arrester- a device for closing electrical circuits by means of an electrical discharge in a gas, vacuum or (less often) a solid dielectric; contains 2 or more electrodes separated by one or more discharge gaps, the conductivity of which changes sharply when the potential difference between the electrodes becomes equal to a certain value determined under given conditions - the breakdown voltage. Depending on the state of the discharge gap and the parameters of the electrical circuit, various forms of discharge can occur in the arresters: spark discharge, glow discharge (including corona discharge), arc discharge, high-frequency discharge or mixed forms. Dischargers are used in electrical engineering and various fields of radio electronics, automation and experimental physics; they serve to protect electrical circuits and devices from overvoltages, to switch high-frequency and high-voltage electrical circuits, they are also used when measuring high voltages, and sometimes as indicators of the degree of vacuum in vacuum systems.

Types of arresters.

In accordance with their functional purpose, there are two main types of arresters - protective and control. Protective arresters help prevent excessive voltage increases on the line or in the installation to which they are connected due to the breakdown of the arrester. The simplest types of arresters used to protect electrical networks are rod and horn arresters, consisting of two electrodes separated by an air gap (respectively in the form of rods or curved horns). One of the electrodes is connected to the protected device, the other is grounded. Since during breakdown the conductivity of the gas-discharge gap increases sharply, the discharge current does not stop even after the voltage drops to a normal value. This current (the so-called accompanying current), which is the current of the system (or installation) to ground, leads to the operation of the relay protection, which entails a temporary interruption of the power supply to the installation or network section. The operation of relay protection in the case of alternating current can be prevented by the use of tubular arresters that provide extinguishing of the accompanying current arc. In tubular arresters, the discharge gap is located in the channel of a tube made of insulating gas-generating material. Under the influence of the heat generated in the accompanying current arc, the tube material decomposes, releasing a large amount of gas; in this case, the pressure in the tube channel increases, a gas flow is formed, extinguishing the arc when the accompanying current passes through zero. Tubular radios are used, as a rule, to protect alternating current power lines from lightning surges.

To ensure effective operation of protective spark gaps, the breakdown voltage of the latter must be highly stable (independent of atmospheric conditions and the state of the electrodes). In addition, the volt-second characteristic of the discharge gap - the curve of the dependence of its breakdown voltage on the rate of voltage rise across it - should be relatively flat and lie below the volt-second characteristic of the insulation of the protected device. These requirements are met by valve arresters, which provide protection against lightning and switching overvoltages for the insulation of transformers and other electrical devices.

Control spark gaps are used to connect various elements of pulse voltage generators in a certain sequence, to connect loads to powerful pulse current sources, as well as to connect elements of electrical circuits of high-voltage test equipment, etc. The simplest control gap is a spherical spark gap, consisting of two spherical electrodes, separated by a layer of gas. In some types of control spark gaps, the discharge between the electrodes is initiated at the right moment by weakening the electrical strength of the discharge gap (for example, by injecting hot gas) or using an ignition pulse.

Types of arresters.

Tubular arrester serves to protect the insulation of overhead lines from atmospheric overvoltages and with other means of protection to protect the insulation of electrical equipment of stations and substations with voltages from 3 kV to 110 kV, weak points on power lines and on the approaches to substations. The connection of tubular arresters to current-carrying parts of power lines is made through an external spark gap.

It is a combination of two spark gaps connected in series (Fig. 1). The first (external) rod span S1 performs the function of limiting lightning overvoltages. The second (internal) gap S2 is located inside the tube 1 made of gas-generating material. One end of the tube is plugged with a grounded metal cap 2 with a rod electrode 3 attached to it. The second end of the tube is open and covered by a ring electrode 4. The internal gap serves to extinguish the electric arc and therefore is also called arc-quenching.

Rice. 1. Tubular arrester.

When limiting overvoltages, two stages of operation of the tubular arrester can be distinguished. At the first stage, when exposed to a lightning impulse, both spark gaps break through and a pulse current flows through them, discharging the overvoltage energy into the ground and thereby limiting it. The volt-second characteristic of a tubular spark gap is determined mainly by the dimensions of the external gap and has a form characteristic of all rod gaps in atmospheric air. Repeated breakdown of the ionized gaps by the operating voltage leads to the ignition of an electric arc between the electrodes. The second stage of operation of the tubular spark gap begins - extinguishing the arc of the accompanying current. Under the influence of the high temperature of the arc, a large amount of gas is released from the inner surface of the tube, increasing the pressure in it to 15 MPa. Gases rush to the open end of the tube and create a blast longitudinal to the burning arc, which allows the arc to be extinguished at the first transition of the current through zero. The activation of the RT is accompanied by the release of a significant amount of hot ionized gases and a strong sound effect.
The tubular arrester is an arc-extinguishing tube made of polyvinyl chloride, with electrodes attached at different ends. One electrode is grounded, and the second is located at a short distance from the protected area (the distance is adjusted depending on the voltage of the protected area). When an overvoltage occurs, both gaps are broken: between the arrester and the protected area and between the two electrodes. As a result of the breakdown, intense gas generation occurs in the tube, and a longitudinal blast is formed through the exhaust hole, sufficient to extinguish the arc.

Valve arrester serves as a means of limiting overvoltages of electrical installation equipment that occur during switching of electrical circuits, lightning strikes, etc.

Rice. 2. Valve (single-phase) arrester.

It consists of spark gaps (1) and nonlinear resistors (2), enclosed in a hermetically sealed porcelain cover (3), which protects the internal elements of the spark gap from the external environment and ensures stability of characteristics.

The valve gap consists of two main components: a multiple spark gap (consisting of several single spark gaps) and a working resistor (consisting of a series set of vilitic disks). The multiple spark gap is connected in series with the operating resistor. Due to the fact that vilit changes characteristics when moistened, the working resistor is hermetically sealed from the external environment. During an overvoltage, a multiple spark gap breaks through, the task of the working resistor is to reduce the value of the accompanying current to a value that can be successfully extinguished by the spark gaps. Vilit has a special property - its resistance is nonlinear - it decreases with increasing current value. This property allows more current to pass with less voltage drop. Thanks to this property, valve arresters got their name. Other advantages of valve-type arresters include quiet operation and no gas or flame emissions.

Magnetic valve arrester(RVMG) consists of several consecutive blocks with a magnetic spark gap and a corresponding number of vilitic disks. Each block of magnetic spark gaps is an alternating connection of single spark gaps and permanent magnets, enclosed in a porcelain cylinder.

When a breakdown occurs in single spark gaps, an arc appears, which, due to the action of the magnetic field created by the ring magnet, begins to rotate at high speed, which ensures faster arc extinguishing compared to valve-type arresters.

Rice. 3. Magnetic valve arrester.

For voltages of 35-500 kV, magnetic valve arresters of the RVM type have been used. They differ from other types of arresters by the presence of blocks of magnetic spark gaps (Fig. 3). Such standard blocks of spark gaps, supplemented with disk vilit resistors, are manufactured for a voltage of 35 kV. The block of magnetic spark gaps consists of a set of single spark gaps 2, separated from each other by ring magnets 3. A single spark gap is made up of two concentrically located copper electrodes 6 and 8, between which an annular slot 7 is formed. The arc arising in the slot rotates under the influence of permanent magnets with high speed, which contributes to its rapid extinguishing. A set of permanent magnets and single spark gaps is placed inside a porcelain cover 1, closed with steel covers 5. The magnets and copper electrodes are tightly compressed by a steel spring 4.

Surge suppressor- This is a spark gap without spark gaps. The active part of such a spark gap consists of a series set of varistors, the conductivity of which depends nonlinearly on the applied voltage.

A spark gap without spark gaps has a particularly fast response: when an overvoltage occurs, the resistance of such a spark gap decreases sharply, increasing immediately after the charge passes (in less than 1 nanosecond). At the same time, the stability of the characteristics of the varistors is maintained after many operations until the end of the specified service life, which eliminates the need for operational maintenance.

Rice. 4. Surge suppressor.

1. Reinforcing elements
2. Varistors
3. New rubber tire
4. Protective tape
5. Flange

Surge arresters in a polymer housing can consist of one or more modules, each of which contains one column of varistors. Varistors do not have a “cumulative” effect, i.e. their current-voltage characteristic does not depend on the number of surge arrester operations. The silicone cover is applied to the active part using direct vacuum casting in a special holding machine. The flanges are connected to each other by two or more glass fiber reinforcements, which gives the arrester high mechanical properties. Due to the fact that the silicone insulation is applied directly to the variators, there is no air inside and, as a result, there are no internal partial discharges. In addition, the cooling conditions for varistors are improved, which improves the energy absorption capacity of the arrester.
The surge arrester consists of an outer insulator made of non-halogenated silicone rubber with end flanges and terminals made of stainless steel, aluminum or copper. The interior of the surge arrester consists of metal oxide varistors, steel gaskets, aluminum components, fiberglass ties and aramid fibers. Metal oxide varistors are agglomerate “tablets” consisting mainly of ZnO (90%) and other substances (more than 1%): Bi 2 O 3, Sb 2 O 3, NiO, Cr 2 O 3 . Metal oxide varistors are covered with a layer of thin glass (<0,1 % веса), содержащим РbО. Силиконовая резина, используемая для внешней изоляции, обладает значительно более высокой гидрофобностью и стойкостью к воздействию ультрафиолетовой радиации, чем фарфоровая изоляция. Кроме того, применение полимерной изоляции снижает массогабаритные параметры ОПН, что расширяет возможность их применения. ОПН могут монтироваться по так называемой «перевернутой» схеме, когда подвод напряжения осуществляется снизу.

6-110 kV surge arresters with polymer insulation, compared to valve-type arresters, have a number of advantages:

1. Varistors used in surge arresters have high stability, which
does not change during long-term operation;

2. high speed of operation of the arrester during switching and
lightning overvoltages;

3. Excellent peak surge arrester performance over a wide operating range
temperature;

4. the use of varistors in a single column design allows
provide particularly deep stress limitation and, accordingly, more
high reliability of equipment operation and improvement of network parameters;

5. reducing the size and weight of surge arresters by 10 - 20 times allows you to install them
directly near the protected equipment;

6. high mechanical strength and low weight of the surge arrester allows
install them on 6-110 kV overhead lines without strengthening the structure of the supports;

7. Surge arresters in a polymer housing do not require special maintenance;
damaged during transportation and storage;

8. The small weight-dimensions of surge arresters make it easy to install them when
minimal use of technology.

General designation of the arrester.

Rice. 5. Designation of arresters.

1. General designation of the arrester
2. Tubular arrester
3. Valve and magnetic valve arrester
4. Surge arrester

Design and principle of operation of arresters

1.General information

Tubular arresters

Valve arresters

DC arresters

Surge suppressors

Long spark gaps

1.General information

When operating electrical installations, voltages arise that can significantly exceed the rated values (overvoltages). These overvoltages can break through the electrical insulation of equipment components and damage the installation. To avoid breakdown of electrical insulation, it must withstand these overvoltages, however, the overall dimensions of the equipment are excessively large, since overvoltages can be 6-8 times higher than the rated voltage. In order to facilitate insulation, the resulting overvoltages are limited using arresters and the insulation of the equipment is selected according to this limited overvoltage value. Occurring overvoltages are divided into two groups: internal (switching) and atmospheric. The first ones arise when switching electrical circuits (inductors, capacitors, long lines), arc faults to ground and other processes. They are characterized by a relatively low frequency of the applied voltage (up to 1000 Hz) and a duration of exposure of up to 1 s. The latter arise when exposed to atmospheric electricity, have a pulsed nature of the applied voltages and a short duration (tens of microseconds). The electrical strength of insulation during pulses depends on the shape of the pulse and its amplitude. The dependence of the maximum pulse voltage on the discharge time is called the volt-second characteristic. Insulation with a non-uniform electric field is characterized by a sharply falling volt-second characteristic. With a uniform field, the volt-second characteristic is flat and runs almost parallel to the time axis.

Fig.1. Coordination of characteristics of the arrester and protected equipment

overvoltage arrester electrical installation

The main element of the spark gap is the spark gap. The volt-second characteristic of this gap (curve 1 in Fig. 1) must lie below the volt-second characteristic of the protected equipment (curve 2). When an overvoltage occurs, the gap must break through before the insulation of the protected equipment. After a breakdown, the line is grounded through the resistance of the arrester. In this case, the voltage on the line is determined by the current I passing through the spark gap, the spark gap and grounding resistance Rз. The lower these resistances, the more effectively overvoltages are limited, i.e. the difference between the possible (curve 4) and the arrester-limited overvoltage (curve 3) is greater. During a breakdown, a current pulse flows through the spark gap.

The voltage across the spark gap during the flow of a current pulse of a given value and shape is called the remaining voltage. The lower this voltage, the better the quality of the arrester. After passing the current pulse, the spark gap becomes ionized and is easily broken through by the rated phase voltage. A short circuit to ground occurs, in which an industrial frequency current flows through the spark gap, which is called accompanying. The accompanying current can vary within wide limits. To avoid switching off the equipment from relay protection, this current must be switched off by the arrester in the shortest possible time (about a half-cycle of the industrial frequency).

The following requirements apply to arresters.

The volt-second characteristic of the arrester should be lower than the characteristic of the protected object and should be flat.

The spark gap of the spark gap must have a certain guaranteed electrical strength at industrial frequency (50 Hz) and during pulses.

The remaining voltage on the arrester, which characterizes its limiting capacity, should not reach values dangerous for the insulation of the equipment.

The 50 Hz follow current must be switched off in the shortest possible time.

The arrester must allow a large number of operations without inspection and repair.

Fig.2. Designation of arresters

On electrical circuit diagrams in Russia, arresters are designated according to GOST 2.727-68.

General designation of the arrester

Tubular arrester

Valve and magnetic valve arrester

The industry produces valve arresters of the RN, RVN, RNA, RVO, RVS, RVT, RVMG, RVRD, RVM, RVMA, RMVU and tubular series.

RN - low voltage arrester, designed to protect the insulation of electrical equipment with a voltage of 0.5 kV from atmospheric overvoltages.

The RVN arrester is a valve type, for protection of electrical equipment insulation from atmospheric overvoltages.

The RNA arrester is designed to protect devices for monitoring the insulation of high voltage bushings of transformers.

The RVRD arrester is a valve type, with a stretching arc, designed to protect the insulation of electrical machines from atmospheric and short-term internal overvoltages.

The RMVU arrester is a valve-type, magnetic, unipolar, designed for overvoltage protection of the insulation of traction electrical equipment in direct current installations.

Arrester RA - series A, is designed to protect against overvoltage the excitation windings of large synchronous machines (turbine generators, hydrogenerators and compensators) with a rated excitation current of up to 3000 A.

RVO arrester - valve-type light-weight design; arrester RVS - valve station; arrester RVT - valve-type, current-limiting; PC - valve arrester for protection of electrical installations for agricultural purposes; arresters of the RVM, RVMG, RVMA, RVMK series - valve-type with magnetic arc extinction, modifications G and A, combined, designed for protection against atmospheric and short-term internal overvoltages (within the capacity of the arresters) insulation of equipment of power stations and alternating current substations with a rated voltage of 15 -500 kV.

Tubular arresters RTV and RTF - vinyl plastic or fiber bakelite, designed to protect the insulation of power lines from atmospheric overvoltages and with other protection means to protect the insulation of electrical equipment of stations and substations with voltages of 3, 6, 10, 35, 110 kV.

Tubular arresters

Fig.3. Tubular arrester

During normal operation of the installation, the tubular arrester (Fig. 3) is separated from the line by an air gap S2. When an overvoltage occurs, the gaps S1 and S2 are broken through and the pulse current is diverted to the ground. After the pulse current passes through the arrester, an accompanying current of industrial frequency flows. An arc lights up in the narrow channel of the holder (tube) 1 made of gas-generating material (vinyl plastic or fiber) in the gap S1 between electrodes 2 and 3. Pressure rises inside the cage. The resulting gases can escape through the hole in the ring electrode 3. When a current passes through zero, the arc is extinguished due to the cooling of the gap S1 by the gases leaving the spark gap. The grounded electrode 4 has a buffer volume 5, where the potential energy of the compressed gas is accumulated. When the current passes through zero, a gas blast is created from the buffer volume, which contributes to the effective extinguishing of the arc.

The maximum switchable current of industrial frequency is determined by the mechanical strength of the holder and is 10 kA for a fiber-bakelite holder and 20 kA for a vinyl plastic holder reinforced with glass fabric on epoxy resin. The accompanying current with a frequency of 50 Hz is determined by the location of the spark gap and varies over a fairly wide range depending on the operating mode of the power system. Therefore, the minimum and maximum values of the short-circuit current at the location where the arrester is installed must be known.

The minimum spark gap current is determined by the extinguishing capacity of the tube. The smaller the diameter of the exhaust channel, the longer its length, the lower the lower limit of the switched-off current. However, at high currents, high pressure arises in the tube. If the mechanical strength of the tube is insufficient, the arrester may be destroyed. Currently, high-strength vinyl plastic arresters with the highest switching current of up to 20 kA are produced.

The operation of a tubular arrester is accompanied by a strong sound effect and the release of gases. Thus, the gas emission zone of the PTB-I10 arrester has the shape of a cone with a diameter of 3.5 and a height of 2.2 m. When placing the arresters, it is necessary that elements at high potential do not fall into this zone.

The protective characteristics of the spark gap largely depend on the volt-second characteristics of the spark gap. In a tubular spark gap, the gap is formed by rod electrodes, which have a steep volt-second characteristic due to the large inhomogeneity of the electric field. At the same time, they strive to make the electric field in the protected devices and equipment uniform in order to make more complete use of insulating materials and reduce size and weight. With a uniform field, the volt-second characteristic turns out to be flat, practically little dependent on time. In this regard, tubular arresters with a steep volt-second characteristic are unsuitable for protecting substation equipment. Typically, they only protect line insulation (the insulation created by pendant insulators). When choosing a tubular arrester, it is necessary to calculate the possible minimum and maximum short-circuit current at the installation site and select the appropriate arrester based on these currents. The rated voltage of the arrester must correspond to the rated mains voltage. The dimensions of the internal S1 and external S2 gaps are selected according to special tables.

Valve arresters

Rice. 4. Valve gap (a) and its spark gaps on an enlarged scale (b)

The PBC-1O type arrester (10 kV station vilitic arrester) is shown in Fig. 4, a. The main elements are vilite rings 1, spark gaps 2 and working resistors 3. These elements are located inside a porcelain casing 4, which at the ends has special flanges 5 for fastening and connecting the spark gap. Working resistors 3 change their characteristics in the presence of moisture. In addition, moisture settling on the walls and parts inside the arrester worsens its insulation and creates the possibility of overlapping. To prevent the penetration of moisture, the arrester casing is sealed at the ends using plates 6 and sealing rubber gaskets 7.

The operation of the arrester occurs in the following order. When an overvoltage occurs, three series-connected blocks of spark gaps 2 break through (Fig. 4b). The current pulse is connected to the ground through the working resistors. The resulting accompanying current is limited by operating resistors, which create conditions for extinguishing the accompanying current arc.

After the breakdown of the spark gaps, the voltage at the spark gap

If the spark gap resistance Rр, determined by the operating resistors, is linear, then the voltage on the spark gap increases in proportion to the current and may become higher than permissible for the equipment being protected. To limit the voltage Uр, the resistance Rр is nonlinear and decreases with increasing current. The relationship between voltage and current in this case is expressed as

where A is a constant characterizing the voltage across the resistance Rp at a current of 1 A; α is the nonlinearity index. The case when α=0 is ideal, since the voltage Up does not depend on the current.

The described arresters are called valve-type, because with pulsed currents their resistance drops sharply, which makes it possible to pass a large current with a relatively small voltage drop.

Fig.5. Volt-ampere characteristic of a vilit resistor

Vilit is widely used as a material for nonlinear resistors. In the region of high currents, its nonlinearity index is α=0.13-0.2. A typical current-voltage characteristic of a villite resistor is shown in Fig. 5, a. At low currents, the resistance Rp is high and the voltage increases linearly with increasing current (region A). At high currents, the resistance decreases sharply and the voltage Uр almost does not increase (region B).

The basis of wilite is SiC carborundum grains with a resistivity of about 10-2 Ohm m. A film of silicon oxide SiO2 10-7 m thick is created on the surface of carborundum grains, the resistance of which depends on the voltage applied to it. At low voltages, the resistivity of the film is 104-106 Ohm m. As the applied voltage increases, the film resistance sharply decreases, the resistance is determined mainly by the carborundum grains and the voltage drop is limited.

Working resistors are made in the form of disks with a diameter of 0.1-0.15 m and a height of (20-60)·10-3 m. Using liquid glass, carborundum grains are firmly bonded to each other.

Vilit is very hygroscopic. To protect against moisture, the cylindrical surface of the disks is covered with an insulating coating. The end surfaces are contact and metallized.

Typically, several working resistors in the form of disks are connected in series (10 disks are shown in Fig. 3a). Given n disks, the remaining voltage is

To reduce the remaining voltage, the number of disks n should be as small as possible.

When current passes, the temperature of the disks rises. When a current pulse of large amplitude but short duration (tens of microseconds) flows, the resistors do not have time to heat up to a high temperature. With prolonged flow of even small currents of industrial frequency (one half-cycle is 10 ms), the temperature can exceed the permissible value, the disks lose their valve properties, and the arrester fails.

The maximum permissible amplitude of a current pulse for a disk with a diameter of 100 mm is 10 kA with a pulse duration of 40 μs. The permissible amplitude of a rectangular pulse with a duration of 2000 μs does not exceed 150 A. The disk passes such currents 20-30 times without damage.

After the pulse current passes through the spark gap, an accompanying current begins to flow, which is a power frequency current. As the current approaches zero, the resistance of the wilite increases sharply, which leads to a distortion of the sinusoidal shape of the current. An increase in circuit resistance leads to a decrease in current and phase angle φ between current and voltage (φ->0). Figure 5b shows the current curves in the working resistor. Here 1 is the source voltage 50 Hz; 2 - circuit current curve determined by inductive reactance X; 3 - curve of the current determined by the working resistor (Rр>>X). Due to the non-linearity of the resistor Rp, the returning voltage (power frequency voltage) decreases. Reducing the speed at which the current approaches zero reduces the arc power in the region of zero current. All this facilitates the process of extinguishing the arc burning between the electrodes of the discharge gap. Thanks to the use of brass electrodes in the spark gaps, after the current passes through zero, a gap is formed near each cathode, the electrical strength of which is 1.5 kV. This ensures that the accompanying current is extinguished during the first passage of the current through zero and makes it possible to extinguish the arc in the spark gaps without the use of special arc extinguishing devices.

The design of the spark gap of the valve gap is clear from Fig. 4, b. The shape of the electrodes ensures a uniform electric field, which makes it possible to obtain a flat volt-second characteristic. The distance between the electrodes is assumed to be (0.5-1) 10-3 m.

The formation of a charge in the closed volume of the spark gap with a short duration of the current pulse is difficult. To facilitate ionization of the spark gap, a micanite gasket is placed between the electrodes. Since the dielectric constant of air is significantly less than that of the mica included in micanite, high electric field gradients arise in the near-electrode volume of air, causing its initial ionization. The resulting electrons lead to the rapid formation of a discharge in the center of the spark gap.

It has been experimentally established that a single spark gap is capable of switching off the accompanying current with an amplitude of 80-100 A at an effective voltage value of 1-1.5 kV. The number of unit gaps is selected based on this voltage. The number of working resistor disks must be such that the maximum current value does not exceed 80-100 A. In this case, arc extinction is ensured in one half-cycle.

To ensure uniform load at industrial frequency, the gaps are shunted with nonlinear resistors 1 (Fig. 4). The thermal resistance of the disks is designed to allow the accompanying current to pass for one or two half-cycles.

Internal overvoltages are low-frequency in nature and can last up to 1 s. Due to its low thermal resistance, vilit cannot be used to limit internal overvoltages. To limit internal overvoltages, the material tervit, similar to vilit, is used, which has high thermal resistance and an increased nonlinearity index α = 0.15-0.29.

Fig.6. Combined arrester with tervit resistors

Tervit disks are used in combined arresters (Fig. 6, a), designed to protect against both internal (switching) and external (atmospheric) overvoltages. During internal overvoltages, both nonlinear resistors HP1 and HP2 operate (curve 1a in Fig. 6b). During atmospheric overvoltages, due to high current, the voltage on HP2 breaks through the gap IP2 and the voltage on the protected line decreases (curve 2).

Valve arresters operate silently. The number of operations is recorded by a special recorder, which is connected between the lower terminal of the arrester and grounding. The most reliable are electromagnetic recorders, the armature of which, when a pulse current passes, acts on the ratchet mechanism of the counting device.

Using the spark gaps shown in Fig. 4b, it is impossible to turn off currents of 200-250 A. In this case, magnetic blast chambers with a permanent magnet are used to extinguish the arc. The arc arising in the spark gap is driven under the influence of a magnetic field into a narrow slot with ceramic machines. On this principle, arresters for voltages up to 500 kV were created. Increasing the diameter of the disks to 150 mm makes it possible to increase their thermal resistance. As a result, combined magnetic-valve arresters make it possible to limit both internal and atmospheric overvoltages.

Main characteristics of the valve arrester:

The extinction voltage Uext is the highest power frequency voltage applied to the arrester, at which the accompanying current is reliably interrupted. This voltage is determined by the properties of the arrester. The power frequency voltage applied to the arrester depends on the circuit parameters. If, during a ground fault of one phase, an overvoltage appears on the free phases, then the extinction voltage applied to the arrester is determined by the equation

where Kz is a coefficient depending on the method of neutral grounding; Unom - rated line voltage of the network. For installations with a grounded neutral Kc = 0.8, for an isolated neutral Kc = l,l.

The quenching current Igash, which is understood as the accompanying current corresponding to the quenching voltage Ugash.

The arc-quenching effect of the spark gap is characterized by the coefficient

where Upr is the breakdown voltage with a frequency of 50 Hz of the spark gap.

The protective effect of a nonlinear resistor is characterized by a protection factor

where Urest is the voltage at the arrester at a pulse current of 5-14 kA. This voltage should be 20-25% lower than the discharge voltage of the protected insulation.

4.DC arresters

Fig.7. DC arrester

To protect installations from DC overvoltages, valve arresters can be used. However, extinguishing a DC arc is much more difficult than alternating current. To use the near-electrode voltage drop, a very large number of spark gaps is required, since the voltage at each pair of electrodes should not exceed 20-30 V.

To extinguish the arc, it is advisable to use magnetic blast using permanent magnets. The resulting electrodynamic force moves the arc at high speed in a narrow slot made of arc-resistant insulating material. As a result of intensive cooling of the arc, its resistance increases and the current stops.

The valve arrester for a network with a voltage of 3 kV DC is shown in Fig. 7. The working resistor 1 consists of two vilitic disks connected to two spark gaps 2 with magnetic arc quenching. Reliable contact between the spaces and the disks is achieved using spring 3, which is also a current-carrying element. The main elements of the arrester are located in a porcelain casing 6, which is closed from below with a lid 7. The arrester is sealed by a lid 4 with a rubber seal 5.

Surge suppressors

Based on zinc oxide, which has a pronounced nonlinearity of the current-voltage characteristic, a series of nonlinear surge suppressors (OSS) for a rated voltage of 110-500 kV has been developed.

The surge arrester is a nonlinear resistor with a high nonlinearity coefficient α=0.04 (vs. 0.1 -0.2 for vilit). It is connected in parallel to the protected object (between the potential output and ground) without discharge gaps. Due to the high non-linearity at the rated phase voltage, a negligible current of 1 mA flows through the arrester. As the voltage increases, the resistance of the arrester sharply decreases, and the current flowing through it increases. At a voltage of 2.2 Uph, a current of 10 flows through the arrester 4A. After the passage of the voltage pulse, the current in the arrester circuit is determined by the phase voltage of the network.

Fig.8. Current-voltage characteristics of the limiter OPN-500

SPDs limit switching overvoltages to the level of 1.8Uph and atmospheric overvoltages to (2-2.4)Uph. From the current-voltage characteristic of the surge arrester-500 (Fig. 8) it is clear that when the overvoltage decreases from 2Uph to Uph, the current flowing through the resistors decreases by 10 6once. The accompanying current flowing after the device is triggered is small (milliamps), just as the power released in the resistors is small. This makes it possible to avoid the sequential connection of several spark gaps and makes it possible to connect the arrester directly to the protected equipment, which significantly increases the reliability of operation.

High nonlinearity of surge arrester resistors (for the high current region α ≈0.04) can significantly reduce overvoltages and reduce the dimensions of equipment, especially at voltages of 750 and 1150 kV. The overall dimensions and weight of surge arresters are much smaller than those of conventional valve arresters of the same voltage class.

Long spark gaps

The authors of the idea of RDI, Podporkin Georgy Viktorovich, Doctor of Technical Sciences, Professor of the Polytechnic University of St. Petersburg, Senior Member of IEEE, and Sivaev Alexander Dmitrievich, Candidate of Technical Sciences, began the first experiments on the development of long-spark dischargers back in 1989, and in 1992 it was obtained certificate of authorship.

Fig.9. Long spark gap circuit

The principle of operation of the arrester is based on the use of the sliding discharge effect, which provides a large length of pulse overlap along the surface of the arrester, and due to this, preventing the transition of the pulse overlap into a power arc of industrial frequency current. The RDI discharge element, along which a sliding discharge develops, has a length several times greater than the length of the line insulator being protected. The design of the arrester ensures its lower impulse electrical strength compared to the protected insulation. The main feature of the long-spark arrester is that due to the long length of the pulsed lightning flashover, the probability of establishing a short circuit arc is reduced to zero.

There are various modifications of RDI, differing in purpose and features of the overhead lines on which they are used.

The main advantage of RDI: the discharge develops along the device through the air, and not inside it. This allows you to significantly increase the service life of products and increases their reliability.

Long-spark loop type arrester (LSLD)

RDIP-10 is designed to protect overhead power lines with a voltage of 6-10 kV three-phase alternating current with protected and bare wires from induced lightning overvoltages and their consequences and is designed for operation outdoors at ambient temperatures from minus 60 °C to plus 50 °C for 30 years.

Long-spark modular arrester (RDIM)

RDIM is designed to protect against direct lightning strikes and induced lightning overvoltages of overhead power lines (OHT) and approaches to substations with voltage of 6, 10 kV three-phase alternating current with bare and protected wires.

RDIM has the best volt-second characteristics, which is why it is advisable to use it to protect sections of the line exposed to direct lightning strikes, as well as to protect approaches to overhead line substations.

RDIM consists of two sections of cable with a cord made of resistive material. The cable sections are folded together so that three bit modules 1, 2, 3 are formed.

The valve gap consists of two main components: a multiple spark gap (consisting of several single spark gaps connected in series) and a working resistor (consisting of a series set of vilitic disks). The multiple spark gap is connected in series with a working resistor. Due to the fact that vilit changes characteristics when moistened, the working resistor is hermetically sealed from the external environment. During an overvoltage, a multiple spark gap breaks through, the task of the working resistor is to reduce the value of the accompanying current to a value that can be successfully extinguished by the spark gaps. Vilit has a special property - its resistance is nonlinear - it decreases with increasing current value. This property allows more current to pass with less voltage drop. Thanks to this property, valve arresters got their name. Other advantages of valve-type arresters include quiet operation and no gas or flame emissions.

Magnetic valve arrester (RVMG)

The RVMG consists of several consecutive blocks with a magnetic spark gap and a corresponding number of vilitic disks. Each block of magnetic spark gaps is an alternating combination of single spark gaps and permanent magnets, enclosed in a porcelain cylinder.

Nonlinear surge suppressor (SPD)

During operation, the insulation of electrical network equipment is exposed to operating voltage, as well as various types of overvoltages, such as lightning, switching, and quasi-stationary. The main devices for protecting networks from lightning and switching overvoltages are valve arresters (VR) and nonlinear surge arresters (OSL). When building or upgrading existing surge protection circuits using surge arresters and surge arresters, it is necessary to solve two main closely related problems:

selection of the number, installation locations and characteristics of devices that will provide reliable insulation protection against lightning and switching overvoltages;
ensuring reliable operation of the devices themselves under quasi-stationary overvoltages, for which they are not intended to limit.

The protective properties of RVs and surge arresters are based on the nonlinearity of the current-voltage characteristics of their working elements, which ensures a noticeable decrease in resistance at elevated voltages and a return to their original state after the voltage is reduced to normal operating voltage. The low nonlinearity of the current-voltage characteristics of the operating elements in the arresters did not allow simultaneously providing sufficiently deep limitation of overvoltages and a low conduction current when exposed to operating voltage, the influence of which was managed by introducing spark gaps in series with the nonlinear element. The significantly greater nonlinearity of the resistances of zinc oxide varistors of surge suppressors made it possible to abandon the use of spark gaps in their design, that is, the nonlinear elements of the surge arrester are connected to the network throughout its entire service life.

Currently, valve arresters are practically out of production and in most cases have served their standard service life. The construction of circuits for protecting the insulation of equipment of both new and modernized substations from lightning and switching overvoltages is now possible only with the use of surge arresters.

The identity of the functional purpose of the RF and arrester and the apparent simplicity of the design of the latter often lead to the fact that the replacement of arresters with surge suppressors is carried out without checking the admissibility and effectiveness of using the installed arrester at the point in the network in question. This explains the increased accident rate of surge arresters.

In addition to the incorrect choice of installation locations and characteristics of surge arresters, another cause of damage to surge arresters is the low-quality varistors used in their assembly, which primarily include Chinese and Indian varistors.

Rod spark gaps

Rod spark gaps, also known as “arc horns,” are used to protect against burnout of protected wires and transfer of single-phase short circuits. in two-phase. For an arc to occur, a short-circuit current exceeding 1 kA is required. Due to the relatively low voltage (6-10 kV versus 20 kV in Finnish networks) and high grounding resistance, arc protection horns do not operate in Russian networks.

Currently, on 6-10 kV overhead lines they are prohibited by the “Regulations on Technical Policy” of the Federal Grid Company.

Long-spark arrester

The principle of operation of the arrester is based on the use of the sliding discharge effect, which provides a large length of pulse overlap along the surface of the arrester, and due to this, preventing the transition of the pulse overlap into a power arc of industrial frequency current. The RDI discharge element, along which a sliding discharge develops, has a length several times greater than the length of the line insulator being protected. The design of the arrester ensures its lower impulse electrical strength compared to the protected insulation. The main feature of the long-spark gap is that due to the long length of the pulsed lightning flashover, the probability of establishing a short circuit arc is reduced to zero.

There are various modifications of RDIs, differing in the purpose and characteristics of the overhead lines on which they are used.

RDI are designed to protect overhead power lines with a voltage of 6-10 kV three-phase alternating current with protected and uninsulated wires from induced lightning overvoltages and their consequences, and direct lightning strikes; designed for outdoor operation at ambient temperatures from minus 60 °C to plus 50 °C for 30 years.

Designation

On electrical circuit diagrams in Russia, arresters are designated according to GOST 2.727-68.
1. General designation of the arrester
2. Tubular arrester
3. Valve and magnetic valve arrester
4. Surge arrester

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Notes

Sources

Rodshtein L. A. Electrical devices: Textbook for technical schools. - 4th ed., revised. and additional - L.: Energoatomizdat. Leningr. department, 1981. - 304 p.: ill.
Protection of 6-35 kV networks from overvoltages / Khalilov F. Kh., Evdokunin G. A., Polyakov V. S., Podporkin G. V., Tadzhibaev A. I. - St. Petersburg: Energoatomizdat. St. Petersburg branch, 2002.- 272 p.
Dmitriev M.V. Application of surge arresters in electrical networks 6-750 kV St. Petersburg 2007

Excerpt characterizing the Discharger

“Who knows what they’re doing,” Denisov grumbled. “Ah! G” skeleton! - he shouted to the cadet, noticing his cheerful face. - Well, I waited.
And he smiled approvingly, apparently rejoicing at the cadet.
Rostov felt completely happy. At this time the chief appeared on the bridge. Denisov galloped towards him.
- Your Excellency! Let me attack! I will kill them.
“What kind of attacks are there,” said the chief in a bored voice, wincing as if from a bothersome fly. - And why are you standing here? You see, the flankers are retreating. Lead the squadron back.
The squadron crossed the bridge and escaped the gunfire without losing a single man. Following him, the second squadron, which was in the chain, crossed over, and the last Cossacks cleared that side.
Two squadrons of Pavlograd residents, having crossed the bridge, one after the other, went back to the mountain. Regimental commander Karl Bogdanovich Schubert drove up to Denisov's squadron and rode at a pace not far from Rostov, not paying any attention to him, despite the fact that after the previous clash over Telyanin, they now saw each other for the first time. Rostov, feeling himself at the front in the power of a man before whom he now considered himself guilty, did not take his eyes off the athletic back, blond nape and red neck of the regimental commander. It seemed to Rostov that Bogdanich was only pretending to be inattentive, and that his whole goal now was to test the cadet’s courage, and he straightened up and looked around cheerfully; then it seemed to him that Bogdanich was deliberately riding close to show Rostov his courage. Then he thought that his enemy would now deliberately send a squadron on a desperate attack to punish him, Rostov. It was thought that after the attack he would come up to him and generously extend the hand of reconciliation to him, the wounded man.
Familiar to the people of Pavlograd, with his shoulders raised high, the figure of Zherkov (he had recently left their regiment) approached the regimental commander. Zherkov, after his expulsion from the main headquarters, did not remain in the regiment, saying that he was not a fool to pull the strap at the front, when he was at headquarters, without doing anything, he would receive more awards, and he knew how to find a job as an orderly with Prince Bagration. He came to his former boss with orders from the commander of the rearguard.
“Colonel,” he said with his gloomy seriousness, turning to Rostov’s enemy and looking around at his comrades, “it was ordered to stop and light the bridge.”
- Who ordered? – the colonel asked gloomily.
“I don’t even know, colonel, who ordered it,” the cornet answered seriously, “but the prince ordered me: “Go and tell the colonel so that the hussars come back quickly and light the bridge.”
Following Zherkov, a retinue officer drove up to the hussar colonel with the same order. Following the retinue officer, fat Nesvitsky rode up on a Cossack horse, which was forcibly carrying him at a gallop.
“Well, Colonel,” he shouted while still driving, “I told you to light the bridge, but now someone has misinterpreted it; Everyone there is going crazy, you can’t understand anything.
The colonel slowly stopped the regiment and turned to Nesvitsky:
“You told me about flammable substances,” he said, “but you didn’t tell me anything about lighting things.”
“Why, father,” Nesvitsky said, stopping, taking off his cap and straightening his sweat-wet hair with his plump hand, “how come you didn’t say to light the bridge when the flammable substances were put in?”
“I’m not your “father,” Mr. Staff Officer, and you didn’t tell me to light the bridge! I know the service, and it’s my habit to strictly carry out orders. You said the bridge will be lit, but who will light it, I cannot know with the Holy Spirit...
“Well, it’s always like this,” Nesvitsky said, waving his hand. - How are you here? – he turned to Zherkov.
- Yes, for the same thing. However, you are damp, let me squeeze you out.
“You said, Mr. Staff Officer,” the colonel continued in an offended tone...
“Colonel,” interrupted the retinue officer, “we must hurry, otherwise the enemy will move the guns to the grape shot.”
The colonel silently looked at the retinue officer, at the fat staff officer, at Zherkov and frowned.
“I’ll light the bridge,” he said in a solemn tone, as if expressing that, despite all the troubles being caused to him, he would still do what he had to do.
Hitting the horse with his long muscular legs, as if it were all to blame, the colonel moved forward to the 2nd squadron, the same one in which Rostov served under the command of Denisov, and ordered to return back to the bridge.
“Well, that’s right,” thought Rostov, “he wants to test me!” “His heart sank and the blood rushed to his face. “Let him see if I’m a coward,” he thought.
Again, on all the cheerful faces of the squadron people, that serious feature appeared that was on them while they were standing under the cannonballs. Rostov, without taking his eyes off, looked at his enemy, the regimental commander, wanting to find confirmation of his guesses on his face; but the colonel never looked at Rostov, but looked, as always at the front, strictly and solemnly. A command was heard.
- Alive! Alive! – several voices spoke around him.
Clinging to the reins with their sabers, rattling their spurs and hurrying, the hussars dismounted, not knowing what they would do. The hussars were baptized. Rostov no longer looked at the regimental commander - he had no time. He was afraid, with a sinking heart he was afraid that he might fall behind the hussars. His hand trembled as he handed the horse to the handler, and he felt the blood rushing to his heart. Denisov, falling back and shouting something, drove past him. Rostov saw nothing except the hussars running around him, clinging to their spurs and clanking their sabers.
- Stretcher! – someone’s voice shouted from behind.
Rostov did not think about what the demand for a stretcher meant: he ran, trying only to be ahead of everyone; but at the bridge itself, without looking at his feet, he fell into viscous, trampled mud and, stumbling, fell on his hands. Others ran around him.
“On both sides, captain,” he heard the voice of the regimental commander, who, riding forward, stood on horseback not far from the bridge with a triumphant and cheerful face.
Rostov, wiping his dirty hands on his leggings, looked back at his enemy and wanted to run further, believing that the further he went forward, the better it would be. But Bogdanich, although he did not look and did not recognize Rostov, shouted at him:
- Who is running along the middle of the bridge? On the right side! Junker, go back! - he shouted angrily and turned to Denisov, who, flaunting his courage, rode on horseback onto the planks of the bridge.
- Why take risks, captain! “You should get down,” said the colonel.
- Eh! he will find the culprit,” answered Vaska Denisov, turning in the saddle.

Meanwhile, Nesvitsky, Zherkov and the retinue officer stood together outside the shots and looked either at this small group of people in yellow shakos, dark green jackets embroidered with strings, and blue leggings, swarming near the bridge, then at the other side, at the blue hoods and groups approaching in the distance with horses, which could easily be recognized as tools.
“Will the bridge be lit or not? Who came first? Will they run up and set fire to the bridge, or will the French drive up with grapeshot and kill them? These questions, with a sinking heart, were involuntarily asked by each of the large number of troops who stood over the bridge and, in the bright evening light, looked at the bridge and the hussars and on the other side, at the moving blue hoods with bayonets and guns.
- Oh! will go to the hussars! - said Nesvitsky, - no further than a grape shot now.
“It was in vain that he led so many people,” said the retinue officer.
“Indeed,” said Nesvitsky. “If only we had sent two young men here, it would have been all the same.”
“Oh, your Excellency,” Zherkov intervened, not taking his eyes off the hussars, but all with his naive manner, due to which it was impossible to guess whether what he was saying was serious or not. - Oh, your Excellency! How do you judge! Send two people, but who will give us Vladimir with a bow? Otherwise, even if they beat you up, you can represent the squadron and receive a bow yourself. Our Bogdanich knows the rules.
“Well,” said the retinue officer, “this is buckshot!”
He pointed to the French guns, which were being removed from their limbers and hastily driving away.
On the French side, in those groups where there were guns, smoke appeared, another, a third, almost at the same time, and at the very minute the sound of the first shot reached, a fourth appeared. Two sounds, one after the other, and a third.
- Oh, oh! - Nesvitsky gasped, as if from burning pain, grabbing the retinue officer’s hand. - Look, one fell, fell, fell!
- Two, it seems?
“If I were a king, I would never fight,” Nesvitsky said, turning away.
The French guns again hastily loaded. The infantry in blue hoods ran toward the bridge. Again, but at different intervals, smoke appeared, and buckshot clicked and crackled across the bridge. But this time Nesvitsky could not see what was happening on the bridge. Thick smoke rose from the bridge. The hussars managed to set fire to the bridge, and the French batteries fired at them no longer to interfere, but so that the guns were aimed and there was someone to shoot at.
“The French managed to fire three grape shots before the hussars returned to the horse guides. Two volleys were fired incorrectly, and all the grapeshot was carried over, but the last shot hit the middle of a group of hussars and knocked down three.
Rostov, preoccupied with his relationship with Bogdanich, stopped on the bridge, not knowing what to do. There was no one to cut down (as he always imagined a battle), and he also could not help in lighting the bridge, because he did not take with him, like other soldiers, a bundle of straw. He stood and looked around, when suddenly there was a crackling sound across the bridge, like scattered nuts, and one of the hussars, who was closest to him, fell on the railing with a groan. Rostov ran towards him along with others. Someone shouted again: “Stretcher!” The hussar was picked up by four people and began to be lifted.
“Ohhh!... Stop it, for Christ’s sake,” the wounded man shouted; but they still picked him up and put him down.
Nikolai Rostov turned away and, as if looking for something, began to look at the distance, at the water of the Danube, at the sky, at the sun. How beautiful the sky seemed, how blue, calm and deep! How bright and solemn the setting sun! How tenderly the water glittered in the distant Danube! And even better were the distant, blue mountains beyond the Danube, a monastery, mysterious gorges, pine forests filled to the top with fog... it was quiet, happy there... “I wouldn’t want anything, I wouldn’t want anything, I wouldn’t want anything, if only I were there,” thought Rostov. “There is so much happiness in me alone and in this sun, and here... groans, suffering, fear and this obscurity, this haste... Here again they shout something, and again everyone runs back somewhere, and I run with them, and here she is.” , here it is, death, above me, around me... A moment - and I will never see this sun, this water, this gorge again”...
At that moment the sun began to disappear behind the clouds; another stretcher appeared ahead of Rostov. And the fear of death and stretchers, and the love of the sun and life - everything merged into one painfully disturbing impression.
“Lord God! He who is there in this sky, save, forgive and protect me!” Rostov whispered to himself.
The hussars ran up to the horse guides, the voices became louder and calmer, the stretcher disappeared from sight.
“What, bg”at, did you sniff pog”okha?...” Vaska Denisov’s voice shouted in his ear.
“It’s all over; but I’m a coward, yes, I’m a coward,” thought Rostov and, sighing heavily, took his Grachik, who had put his leg out, from the hands of the handler and began to sit down.

During switching or under the influence of lightning discharges, high voltage pulses several times higher than the rated value may occur in electrical equipment and power lines. Since the insulation is not designed for such voltage, its breakdown may occur, accompanied by an accident. To prevent it, electrical devices (arresters) are used to protect against overvoltage pulses.

Arrester device and principle of operation

Any spark gap has electrodes, the distance between which is called the spark gap and the arc extinguishing device. One electrode is connected to the equipment being protected, and the other is grounded. When the voltage increases above the value determined by the size of the gap between the electrodes, it breaks through and the overvoltage pulse is discharged through grounding.

The main parameter of limiters is the guaranteed electrical strength at rated voltage. This means that the device will under no circumstances work in a normal situation. At the moment the pulse passes, the arc extinguishing device is turned on. It must quickly (within half a cycle) eliminate the short circuit formed by the arc, so that the overload protection devices do not have time to operate.

The catalog of manufactured devices allows you to make a choice of arresters that most fully meet the requirements and are preferable in price.

Air (tubular) arresters are made in the form of tubes made of polymer, which when heated can release large amounts of gas. Electrodes are fixed at the ends of the tube, the distance between which determines the magnitude of the response voltage. During a breakdown, the tube material begins to release gas, which, escaping through a hole in the housing, creates a blast that extinguishes the electric arc. The response voltage exceeds 1 kV.

Gas varieties structurally similar to previous models. The sample is carried out in a sealed ceramic tube containing an inert gas. Ionization of the gas ensures faster response, and its pressure reliably extinguishes the arc. The response threshold can be from 60 volts to 5 kV. A neon light is often used to indicate overvoltage.

Valve devices consist of several spark gaps connected in series and a resistance made up of vilitic disks (working resistor). They are connected to each other in series. Since the characteristics of vilit depend on humidity, it is placed in an airtight shell.

During a breakdown, the resistor's task is to reduce the short-circuit current to a value that can be successfully extinguished by the spark gaps. Since the value of the resistance is nonlinear - the greater the current, the smaller it is, this makes it possible to pass a significant current with a small voltage drop. The advantages of these devices include operation without noise and light effects. Wikipedia characterizes these arresters as obsolete and no longer in production.

Magnetic valve modifications assembled from a number of blocks equipped with magnetic spark gaps and an equal number of viliton disks. A single unit consists of a series of spark gaps connected in series and a permanent magnet, placed in a porcelain housing. At the moment of breakdown, the resulting arc, under the influence of the magnetic field generated by the ring magnet, acquires rotation, and therefore is extinguished faster than in valve devices.

In long-spark devices The phenomenon of a sliding discharge is used, providing a significant length of the pulse path along the outside of the discharge element. The length of the discharge element is significantly longer than the insulator of the power line, but its electrical strength is less, so the possibility of an arc occurring is zero. This type is used on 3-phase power lines. They can operate at temperatures from - 60° C to + 50° C for 30 years.

There are no spark gaps in nonlinear surge suppressors. Instead, series-connected zinc oxide varistors are used. Their resistance is lower, the greater the current strength, so the removal of the overvoltage pulse occurs very quickly with an immediate return to its original position. To pass large currents, parallel installation of several limiters of the same brand is allowed. The limiter is installed for the entire service life of the protected object.

Selection of arresters

First of all, you need to decide on the class of the device:

In accordance with the specified ranking, selective protection schemes are created. The most popular is the B - C circuit, which reliably protects against overvoltage of 1.5 - 2.5 kV. To protect expensive electronic equipment, protection from A to D inclusive is constructed.

Selection by parameters

Select a specific protective device, operating on arresters or varistors, is needed according to the following parameters:

The remaining values specified in the technical data sheet are needed for testing and setting up protection systems at industrial enterprises. Since creating an overvoltage protection system is a responsible matter, if there is no experience, it is better to entrust the installation of arresters and grounding to specialists.

Purpose of arresters

Gas-filled arresters are devices with two or three electrodes designed to protect electronic equipment from accidental overvoltages or to generate powerful electrical pulses in the micro- and nanosecond ranges. The main feature of the current-voltage characteristic of a two-electrode protective spark gap is the presence of a threshold voltage, below which the spark gap acts as an insulator, and above it as a low-resistance conductor.

Before switching to a conducting state, switching arresters are equivalent to an open switch. They switch to the low-resistance conductor mode when the voltage increases above a threshold value or when a voltage pulse arrives at the control electrode (in controlled arresters). Protective and switching arresters return from a conducting state to a non-conducting state only after the voltage between the main electrodes has decreased to a certain value.

In a conducting state, due to their low intrinsic resistance, the arresters do not detect the current value. Usually it is limited by the active (or inductive) resistance of the circuit elements. Characteristic parameters of arresters: threshold voltage - from 70 V to 300 kV, permissible current - up to 150 kA. For some types of arresters (protection of circuits under relatively high operating voltage), the parameters indicate the voltage at which the arrester returns to a non-conducting state. Typical voltage values are from 50 V to 8 kV. Important parameters of switching arresters are the maximum permissible pulse repetition rate (10 - 100 Hz) and service life, which is characterized by the guaranteed number of switchings (106 - 107) or the charge switched over the entire period of operation (103 - 104 C - “total charge”).

Device and principle of operation

The design of a typical arrester consists of two flat disk electrodes separated by a dielectric vacuum ceramic shell (Fig. 1). Devices are usually filled with inert gases and their mixtures to a pressure of 102 to 106 Pa. Characteristic values of the parameters of the gas-discharge gap: distance - up to 1 cm, area - about 1 cm Minimum dimensions 8.26 mm (diameter and height of dischargers of a “push-button” design), maximum - 120220 mm. The spark gaps enter the conducting state as a result of the occurrence of a gas discharge. Depending on the purpose of the device, the discharge can be glow (in the milliamp current range), arc (amps and kiloamps) or spark (kiloamps).

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The main physical processes in a glow discharge: the development of electron avalanches, the release of electrons from the cathode under the influence of ions and photons, the redistribution of potential in the gap due to the ionic space charge, leading to the formation of a narrow near-cathode region with a high field strength. The characteristic values of the discharge voltage are hundreds of volts.

In an arc discharge, the decisive role is played by the thermal emission of electrons from the surface of the cathode heated by ion bombardment. An arc discharge, in comparison with a glow discharge, has lower combustion voltage values - tens of volts. The spark gaps are characterized by a “transient form of arc discharge”, in which not the entire cathode is quickly heated to a high temperature, but only a microsection of it, within which melting and evaporation of the substance is possible.

A discharge under such conditions can develop in an expanding vapor cloud of the cathode material. To ensure the necessary durability of the arresters in such cases, special attention is paid to the choice of cathode material. The main requirements for it are low electron work function and relatively low heat of evaporation. One common material is cesium aluminum silicate, which fills the pores of a pressed nickel powder sponge. In high-current (up to 150 kA) switching arresters, the cathode is made in the form of a copper film deposited on a molybdenum sublayer.

A spark discharge develops at a very high intensity of electron multiplication in an avalanche, with a significant generation of photons capable of ionizing gas molecules. The discharge is formed in the form of “streamers”, visually observed as sparks. The development of streamers physically corresponds to the rapid movement of the front of the ionized gas, due to the fact that after part of the electrons of the avalanche leave the anode, the positive space charge “pulls” into the main discharge channel “daughter” electron avalanches that originate in front of the front as a result of photoionization of gas molecules.

Advantages of arresters: wide range of operating voltages and currents, resistance to current overloads, simplicity of design and manufacturing technology, ability to function normally under conditions of radiation and high (up to 300 °C) ambient temperatures. The advantages determine the widespread use of arresters: currently about 50 types of devices are produced. The type designation usually includes the letter "P" and the design number, for example the R-150 uncontrolled surge arrester. Some types are designated with two letters and a number. For example, RU-73 is a controlled three-electrode spark gap; RO-49 - sharpener spark gap for X-ray devices; RK-160 - switching arrester.