Gas-insulated column switch 110 kV forum. What is a SF6 circuit breaker and why is it needed? Principle of operation and scope

In order to extinguish an electric arc, many different gas mixtures are often used. According to this principle, the equipment filled with SF6 gas, which is used for work in an emergency, works. In this article, we will consider the device, the principle of operation and the purpose of SF6 circuit breakers.

What does the equipment consist of and what are the designs?

The SF6 high voltage circuit breaker is a device whose purpose is to control and monitor a high voltage power supply line. The design of such equipment resembles the mechanism of an oil device, only for extinguishing a combination of gases is used instead of an oil mixture. As a rule, sulfur is used. Unlike an oil-based appliance, SF6 does not require special care. Its main advantage is durability.

SF6 circuit breakers are divided into:

1. Kolinsky. The use of such a structure is optimal only for a 220 kV network. This disconnecting device operates on a single phase. The design includes two systems that are placed in a tank with SF6 gas. This is a contact and arc extinguishing system. Also, they can be both manual and remote. This is considered the main reason for their large size.
2. Tank. The dimensions are smaller than column ones. The design has an additional drive, which has several phases. Thanks to this, you can smoothly and gently adjust the on and off voltage. And due to the fact that a current transformer is built into the system, the mechanism is able to carry heavy loads.

According to the method of extinguishing the electric arc, SF6 circuit breakers are divided into:

• air, it is also called autocompression;
• rotating;
• longitudinal blast.

Principle of operation and scope

How does a high voltage SF6 circuit breaker work? Due to the isolation of the phases from each other by means of SF6 gas. The principle of operation of the mechanism is as follows: when a shutdown signal is received electrical equipment, the contacts of each chamber open. Built-in contacts create an electric arc, which is placed in a gaseous environment.

This medium separates the gas into individual particles and components, and due to high pressure in the tank, the medium itself is reduced. Possible use of additional compressors if the system operates at low pressure. Then the compressors increase the pressure and form a gas blast. Shunting is also used, the use of which is necessary to equalize the current.

The designation in the diagram below indicates the location of each element in the circuit breaker mechanism:

As for tank-type models, control is carried out with the help of drives and transformers. What is the drive for? Its mechanism is a regulator and its purpose is to turn the power on or off and, if necessary, to keep the arc at a set level.

Drives are divided into spring and spring-hydraulic. Springs have a high degree of reliability and have a simple principle of operation: all work is done thanks to mechanical parts. The spring is capable of compressing and decompressing under the action of a special lever, as well as being fixed at the set level.

Spring-hydraulic drives of circuit breakers additionally have a hydraulic control system in their design. Such a drive is considered more efficient and reliable, because the spring device itself can change the level of the latch.

Advantages and disadvantages of equipment

As in any structures and mechanisms, SF6 circuit breakers have their own advantages and disadvantages. The advantages of the device include:

1. Multifunctionality. The purpose and application of such a mechanism is possible for any voltage in the network.
2. Action speed. SF6 reacts to the presence of an electric arc in a matter of seconds. Thanks to this, in the event of an emergency, it is possible to quickly turn off the controlled system.
3. Possible use in vibration and fire hazard conditions.
4. Longevity. No need to replace gas mixtures. Contacts that come into contact with mixtures are almost not subject to wear, and the outer case has a high level of protection.
5. Can be used on networks high voltage. Their analogues, such as vacuum devices, are not capable of doing this.

But these switches also have their drawbacks. For example:

1. Since the production of devices is very complex and SF6 mixtures are expensive, the price of the design itself is high.
2. The device does not work at low temperatures.
3. When maintenance is required, specific equipment must be used.
4. The device must be installed on a special platform or foundation, and for this you must have experience and special instructions.

So we examined the device, purpose and principle of operation of SF6 circuit breakers. We hope that the information provided was useful and interesting for you!

You probably don't know:

General information

SF6 circuit breakers VGT series are designed for switching electrical circuits under normal and emergency conditions, as well as operation in automatic reclosure cycles in three-phase alternating current networks with a frequency of 50 Hz and a rated voltage of 110 and 220 kV.

Symbol structure

switch VGT-XII * -40/2500U1:
VG - SF6 circuit breaker;
T - symbol design;
X - rated voltage, kV (110 or 220);
II * - category according to the length of the creepage distance along the external insulation
in accordance with GOST 9920-89;
40 - rated breaking current, kA;
2500 - rated current, A;
U1 - Climatic performance and placement category according to GOST
15150-69 and GOST 15543.1-89. drive PprK-1800S:
P - drive;
Pr - spring;
K - cam;
1800 - work of static inclusion, J;
S is special.

Operating conditions

Installation height above sea level is not more than 1000 m. Ambient temperature is from minus 45 to 40°C. Relative Humidity air no more than 80% at a temperature of 20°C. Upper value 100% at 25°C. The wind speed is 15 m/s with ice with an ice crust thickness of up to 20 mm, and in the absence of ice up to 40 m/s. The environment is non-explosive, not containing aggressive gases and vapors in concentrations that destroy metals and insulation. The content of corrosive agents according to GOST 15150-69 (for atmosphere type II). The tension of the wires applied in the horizontal direction is not more than 1000 N. The length of the creepage distance of the external insulation complies with the GOST 9920-89 standards for substation insulation (pollution degree II *, performance category B) - for 110 kV - at least 280 cm, for 220 kV - not less than 570 cm. The switches comply with the requirements of GOST 687-78 "AC switches for voltage over 1000 V. General specifications"and TU 2BP.029.001 TU, agreed with RAO "UES of Russia". TU 2BP.029.001 TU

Specifications

The main technical data of the switches are given in the table.

The switches perform the following operations and cycles: 1) disconnection (O);
2) inclusion (B);
3) inclusion - disconnection (VO), including - without deliberate time delay between operations (B) and (O);
4) disconnection - inclusion (OB) at any non-contact pause, starting from t to, corresponding to t;
5) disconnection - inclusion - disconnection (OVO) with time intervals between operations in accordance with p.p. 3 and 4;
6) switching cycles: 0-0.3 s - VO-180 s - VO;
O-0.3 s - VO-20 s - VO;
O-180 s - VO-180 s - VO. The number of tripping operations allowed for each pole of the circuit breaker without inspection and repair of arcing devices (resource for switching resistance) is: at currents in the range over 60 to 100% of the rated tripping current - 20 operations;
at currents in the range over 30 to 60% of the rated breaking current - 34 operations;
at operating currents equal to the rated current - 3000 operations B-t on. The allowable number of operations B for short circuit currents should be no more than 50% of the allowable number of operations O; the allowable number of operations V at load currents is equal to the allowable number of operations O. The switches have the following indicators of reliability and durability: overhaul - 5000 cycles B-t on;
service life before the first repair - 20 years, if before this period the resources for mechanical or switching resistance are not exhausted;
service life - 40 years. Warranty period of operation - 5 years with an operating time not exceeding the values ​​​​of resources for mechanical or switching resistance, is calculated from the day the circuit breaker is put into operation, but no later than 6 months for operating enterprises and 9 months - for enterprises under construction from the day the products arrive at the enterprise.

Switches of the VGT series are high voltage electrical switching devices, in which SF6 is the quenching and insulating medium. Circuit breaker VGT-110II * (Fig. 1) consists of three poles (columns) mounted on a common frame and mechanically connected to each other. All three poles of the circuit breaker are controlled by one spring drive type PPRK-1800S.

General view, overall, mounting and connecting dimensions of the circuit breaker VGT-110II * -40/2500U1: 1 - spring drive;
2 - pole (column);
3 - conclusion;
4 - disconnecting device;
5 - tube;
6 - signaling device;
7 - frame;
8 - position indicator;
9 - cable box;
10 - M16 bolt;
11 - ground sign;
12 - frame support Circuit breaker VGT-220II * (Fig. 2) consists of three poles, each of which has its own frame and is controlled by its own drive.

General view, overall, installation and connecting dimensions switch VGT-220II * -40/2500U1: 1 - spring drive;
2 - column (arcing device);
3 - tire;
4 - output;
5 - frame;
6 - disconnecting device;
7 - position indicator;
8 - capacitor;
9 - bolt M16;
10 - ground sign;
11 - frame support The principle of operation of the circuit breakers is based on the extinguishing of an electric arc by a flow of SF6 gas, which is created due to the pressure drop provided by self-generation, i.e. due to the thermal energy of the arc itself. The circuit breakers are closed by the energy of the closing springs of the drive, and they are opened by the energy of the spring of the circuit breaker opening device. The frame of the VGT-110 circuit breaker is a welded structure, on which a drive, a disconnecting device, columns and electrocontact pressure alarms are installed. In the cavity of one of the supporting channels of the frame, closed with covers, there are series-connected rods connecting the drive lever with the levers of the poles (columns). The cover has a viewing window for the switch position indicator. The frame has four holes with a diameter of 36 mm for fixing to the foundation posts and is equipped with a special bolt for connecting the grounding bar. The pole frame of the VGT-220II * circuit breaker has a similar design. The disconnecting device is installed on the end of the frame opposite from the drive and consists of a disconnecting spring, which is compressed when the switch is turned on by a rod connected to the outer lever of the extreme column. The spring is located in a cylindrical housing, on the outer flange of which there is a buffer device designed to dampen the kinetic energy of moving parts and serve as a stop (travel limiter) when the circuit breaker is dynamically closed. The VGT-110 circuit breaker pole is a column filled with SF6 gas and consisting of a support insulator, an arcing device with current outputs, and a control mechanism with an insulating rod. The pole of the VGT-220II * circuit breaker consists of two columns, the arcing devices of which are mounted on support insulators and connected in series by two busbars. Shunt capacitors are connected in parallel to the arcing devices for uniform voltage distribution. SUBSTANCE: arc-extinguishing device contains openable main and arc-extinguishing contacts provided with arc-resistant tips, a piston device for creating pressure in its internal cavity and fluoroplastic nozzles, in which SF6 flows acquire the direction necessary for effective arc extinguishing. The above-piston high-pressure cavity and the under-piston cavity are equipped with a valve system that allows for efficient blowing in the arc burning zone in all switching modes. In the upper part of the arc extinguishing device there is a container filled with an activated adsorbent that absorbs moisture and decomposition products of SF6 gas from the gas region. In the on position, the main and arcing contacts are closed. When switching off, the main contacts are first opened with almost no arc effect, with the arcing contacts closed, and then the arcing contacts are opened. Sliding contact between the fixed sleeve of the piston device and the housing of the movable contact is carried out by contact elements laid in its recesses, having the form of closed wire spirals. The column control mechanism is located in the housing and the support insulator and consists of a splined shaft with an external and internal lever. The splined shaft is mounted in bearings and sealed with cuffs. The inner lever is connected to the movable contact rod through an unregulated insulating rod. An autonomous sealing valve is built into the body of the mechanism, through which, with the help of copper tube a pressure switch mounted on the frame of the switch is connected. The self-sealing valve consists of a body and a spring-loaded valve, a signaling tube connection unit and a plug installed during transportation and after filling with SF6 during commissioning to ensure reliable sealing of the internal cavity of the column. The indicating type electrocontact pressure switch is equipped with a temperature compensation device that brings the pressure readings to a temperature of 20 ° C, and two pairs of contacts closed at the operating pressure of the switch. The first pair of contacts opens when the pressure drops to 0.34 MPa, signaling the need to replenish the pole, the second pair opens at a pressure of 0.32 MPa, blocking the command to the control electromagnets. To exclude false signals in case of possible activation of contacts from vibration when turning on and off the circuit breaker, and also due to their low power, an intermediate time relay (for example, RP-2556 or RP-18) with a time delay of 0.8 to 1.2 s must be included in the contact circuit. The signaling device is closed with a special casing that protects it from direct contact with precipitation and sun rays. The circuit breaker drive is spring-loaded with motor and manual winding of working (cylindrical, helical) springs, type PPrK-1800S. The drive is a separate, placed in a sealed three-door wardrobe, unit. The drive has two tripping electromagnets; equipped with devices that block: passage of a command to the closing electromagnet when the circuit breaker is on and the springs are not charged;
passing the command to the tripping electromagnet when the circuit breaker is off;
"idle" (when the switch is on), dynamic discharge of the working springs;
turning on the electric motor of the spring plant when manually winding them. The drive allows: to have an alarm about the following deviations from its normal (working) state: the SF circuit breaker is not switched on;
malfunction in the spring plant system;
automatic control of the electric motor is not included;
springs not cocked;
slowly operate the switch contacts when setting it up without any additional (for example, jack) devices. The drive has anti-condensation (non-switchable) and main (thermostat-controlled) electrical heating of the cabinet. The fundamental difference between the PPrK-1800S drive and other drives of the PPrK family is the presence of a buffer that slows down the moving parts of the circuit breaker when it is turned off. The drive is easy to adjust, troubleshoot and maintain. At correct operation reliable at work. The drive control scheme is shown in fig. 3.

PPrK-1800S drive control circuit diagram: a - version with motor power supply from 380 V mains;
b - version with motor power supply from 220 V network

Tab. 1 to fig. 3

Tab. 2 to fig. 3

Note. The position of the contacts of the circuit elements corresponds to the off position of the circuit breaker, the discharged state of the operating springs of the drive and the position of the fist cocking them, in which the finger of the latter does not act on the lever that controls the SQ2 contacts.

The delivery set of the VGT-110II circuit breaker * includes: a frame with a drive, three poles (columns) filled with SF6 gas up to transport pressure, a single set of accessories and spare parts. The delivery set of the VGT-220II circuit breaker * includes: three frames with drives, six columns filled with SF6 gas up to transport pressure, six connecting busbars, six capacitors of the DMK-190-0.5 type, a set of capacitor mounting parts, a single set of accessories and spare parts . The delivery set of each circuit breaker also includes a passport, a manual for the circuit breakers, a manual for the drive, a list of equipment, a list of spare parts and accessories, a set of documents for purchased products. In addition, for a group of circuit breakers (1-3 circuit breakers supplied to one address), at the request of the customer, a group set of spare parts and accessories is supplied, which includes: cylinders with SF6 gas, a filter for drying SF6 gas, gas hoses with fittings special tool and fixtures.

Various gas mixtures are often used to extinguish an electric arc. 110 kV and 220 kV SF6 circuit breakers operate exactly on this principle and can be used for emergency operation.

Design and types

SF6 high-voltage circuit breakers are operational control devices for monitoring high voltage line power supply. These devices have a very similar design with oil ones, but at the same time, they use not an oil mixture to extinguish the arc, but a combination of gases. Often it is sulfur. Oil circuit breakers require special care: according to the norms, periodic oil changes and cleaning of working contacts are necessary. SF6 does not need this. The main advantage of SF6 is its durability: it does not age and minimally pollute the mechanical parts of the device.

They are:

1. Kolinsky (HPL 245B1, MF 24 Schneider Electric);
2. Tank (ABB 242PMR, DT2-550 F3 - manufacturer Areva).

The column SF6 circuit breaker is a standard single-phase switching device (eg LF 10 from Schneider Electric). It is used for 220 kV network. Structurally, they consist of two systems: contact and arc extinguishing. Both of them are located in a container filled with SF6 gas. They can be either manual (control is carried out exclusively mechanically) or remote. Because of this division, they have rather large overall dimensions.

The tank ones have smaller dimensions, they are complemented by the PPRM 2 drive for the SF6 circuit breaker. The drive is divided into several phases, which allows for soft voltage regulation (on and off). Also, their advantage is that they can carry heavy loads thanks to the current transformer built into the system.

In addition to design features, SF6 circuit breakers are classified according to the principle of arc quenching:

1. Autocompression or air;
2. Rotating;
3. Longitudinal blast;
4. Longitudinal blast with additional SF6 heating.

Principle of operation and purpose

SF6 high voltage circuit breakers operate by isolating the phases from each other by means of SF6 gas. When a signal is triggered that it is necessary to turn off the electrical equipment, the contacts of individual cameras (if the device is columnar) open. Thus, the built-in contacts form an arc that is placed in a gaseous medium. It decomposes the gas into individual components, but at the same time it itself decreases due to the high pressure in the tank. If the system is installed at low pressure, then additional compressors are used to pressurize and create a gas blast. Shunting is additionally used to equalize the current. Visually, the scheme of work looks like this:

Separately, it must be said about tank-type models. Their control is carried out by drives and transformers. The drive mechanism for this installation is a regulator: it is necessary to turn on, off electrical energy and holding the arc (if necessary) at a certain level. Drives are:

1. Spring;
2. Spring-hydraulic.

Spring has a very simple principle of operation and high level reliability. In it, all the work is done only by mechanical parts. The spring is clamped and fixed at a certain level, and when the position of the control lever is changed, it is unclenched. Based on its principle of operation, a scientific presentation of the action of sulfur hexafluoride in the electrical environment is often prepared.

Modern spring-hydraulic drives, in addition to the spring, are additionally equipped with hydraulic system management. They are considered more efficient, because the spring mechanisms themselves can change the position of the latch.

Advantages of SF6 circuit breakers:

1. Versatility. These switches are used to control networks with any voltage;
2. Speed ​​of action. SF6 reactions to the presence of an electric arc occur in a fraction of a second, which allows for a quick emergency shutdown of the controlled system;
3. Are suitable for operation in the conditions of fire danger and vibration;
4. Durability. Contacts in contact with SF6 gas practically do not wear out, gas mixtures do not need to be replaced, and outer shell high performance protection;
5. They are suitable for switching off high voltage AC and DC, while their vacuum models cannot be used on high voltage networks.

But, such devices have certain limitations:

1. High price due to the complexity of production and the high cost of the SF6 gas mixture;
2. Installation is carried out only on a foundation or a special electrical panel, and this requires special instructions and experience;
3. Switches do not work at low temperatures;
4. When maintenance is required, special equipment must be used.

Video: features of SF6 circuit breakers

Specifications

Consider specifications switches different manufacturers and types of work.

MEK SF6 SF6 spring circuit breaker HD4 (factory ABB - ABB):

VGBEP-35 (VGB-35, VGBE):

VGT-35 (VMT-35):

Kolinsky VGT-110:

VGU-110 (gas power):

Column switch GL314 Alstom:

Generator circuit breakers with spring drive - FKG 2:

SF6 gas compression circuit breaker from Siemens (Siemens) 3AP1FG-245 (foundations are needed for installation):

You can buy suitable SF6 circuit breakers at any electrical supply store. Their cost depends on the type of device and its manufacturer. The price list in Samara, Moscow, Yekaterinburg and other cities varies from $100 to several thousand.

High-voltage circuit breakers using SF6 gas as an insulating and arcing medium are becoming more and more widespread, as they have high switching and mechanical resources, breaking capacity, compactness and reliability compared to air, oil and low-oil high-voltage circuit breakers.

Advances in the development of SF6 circuit breakers directly had a significant impact on the introduction of compact outdoor switchgear, ZRU and GIS GIS. In SF6 circuit breakers, various ways arc extinguishing depending on the rated voltage, rated breaking current and characteristics of the power system (or individual electrical installation).

In SF6 arc extinguishers, in contrast to air arc extinguishers, when the arc is extinguished, the gas outflow through the nozzle does not occur into the atmosphere, but into the closed volume of the chamber filled with SF6 gas at a relatively small overpressure.

According to the method of extinguishing the electric arc during shutdown, the following SF6 circuit breakers are distinguished:

1. Autocompression SF6 circuit breaker, where required mass flow SF6 through the nozzles of the compression arcing device is created along the movable system of the circuit breaker (autocompression circuit breaker with one pressure stage).

2. SF6 circuit breaker with electromagnetic blast, in which arc quenching in the arc extinguishing device is ensured by its rotation along the ring contacts under the action of magnetic field created by the current to be switched off.

3. SF6 circuit breaker with high and low pressure, in which the principle of providing gas blast through the nozzles in the arc extinguisher is similar to air arc extinguishers (SF6 circuit breaker with two pressure stages).

4. Auto-generating SF6 circuit breaker, where the required mass flow of SF6 gas through the nozzles of the arc quenching device is created by heating and increasing the pressure of the SF6 gas by a tripping arc in a special chamber (auto-generating SF6 circuit breaker with one pressure stage).

Consider some typical designs SF6 circuit breakers for 110 kV and above.

SF6 circuit breakers 110 kV and above for one break various firms have the following nominal parameters: Unom=110-330 kV, Inom=1-8 kA, Io.nom=25-63 kA, SF6 pressure pnom=0.45-0.7 MPa(abs), shutdown time 2-3 periods short circuit current. Intensive research and testing of domestic and foreign companies made it possible to develop and put into operation a SF6 circuit breaker with one break at Unom = 330-550 kV at Io.nom = 40 - 50 kA and current off time of one short-circuit current period.

A typical design of an auto-compression SF6 circuit breaker is shown in fig. one.

The device is in the off position and contacts 5 and 3 are open.

Rice. one.

The current supply to the fixed contact 3 is carried out through the flange 2, and to the moving contact 5 through the flange 9. top cover 1, a chamber with an adsorbent is mounted. The supporting insulating structure of the SF6 circuit breaker is fixed on the footboard 11. When the switch is turned on, the pneumatic actuator 13 is activated, the rod 12 of which is connected through the insulating rod 10 and the steel rod 8 to the movable contact 5. The latter is rigidly connected to the fluoroplastic nozzle 4 and the movable cylinder 6. The entire EV movable system (elements 12-10-8-6-5) moves upward relative to the fixed piston 7, and the cavity K of the circuit breaker arcing system increases.

When the switch is turned off, the rod 12 of the drive power mechanism pulls the movable system down and a high blood pressure compared to the pressure in the circuit breaker chamber. Such auto-compression of SF6 gas ensures the outflow of the gaseous medium through the nozzle, intensive cooling of the electric arc that occurs between contacts 3 and 5 when it is turned off. The position indicator 14 gives the initial position of the circuit breaker contact system. In a number of designs of autocompression SF6 circuit breakers, spring, hydraulic power drives are used, and the flow of SF6 gas through the nozzles in the arc chute is carried out according to the principle of double-sided blowing.

On fig. 2 shows a tank SF6 circuit breaker of the VGBU type 220 kV (Inom = 2500 A, Io.nom = 40 kA JSC NIIVA with an autonomous hydraulic drive 5 and built-in current transformers 2. The EV has a three-phase control (one drive for three phases) and is equipped with porcelain (polymer) tires 1 air-SF6 bushings.

In the gas-filled tank 3 there is an arcing device, which is connected to the hydraulic drive 5 through a transmission mechanism located in the gas-filled chamber 4. The design of the tank SF6 circuit breaker is fixed on a metal frame 6. To fill the circuit breaker with SF6 gas, connector 7 is used. is equal to one atm (abs.) and then it is necessary to provide р = рnom.

Rice. 2.

The advantages of tank SF6 circuit breakers with built-in current transformers over the "column SF6 circuit breaker plus a separate current transformer" kits are: increased seismic resistance, smaller area of ​​the alienated territory of the substation, smaller volume of required foundation works during the construction of substations, increased safety of the substation personnel (arcing devices are located in grounded metal tanks), the possibility of using SF6 heating when used in areas with a cold climate.

In designs of tank circuit breakers of 220 kV and above, an increase in nominal pressure SF6 gas (pnom > 4.5 atm (abs.)); therefore, heating of the gaseous medium is introduced in order to prevent SF6 liquefaction at low temperatures environment or mixtures of SF6 with nitrogen or tetrafluoromethane are used.

As practice shows, for a rated voltage of 330–500 kV, tank circuit breakers with one break for rated currents of 40–63 kA are the most promising type. switching equipment for outdoor switchgear and switchgear.

The circuit breaker VGB-750-50/4000 U1 developed by OAO NIIVA (Fig. 3) with a two-break auto-compression arcing device, built-in current transformers, air-SF6 polymer bushings is equipped with two hydraulic actuators per pole, which makes it possible to ensure a total shutdown time of not more than the duration of two periods of industrial frequency current.

In the on position of the SF6 circuit breaker, the resistors are shunted by the main contacts. When disconnected, the resistor contacts open first, then the main contacts, then the arcing contacts. When switched on, the resistor contacts close first, followed by the arcing and main contacts. To equalize the voltage distribution, each gap is shunted with capacitors.

Column SF6 circuit breakers with one break per rated voltage of 110-220 kV with rated current disconnection 40-50 kA.

Rice. 5

A typical design of a column-type SF6 circuit breaker of the VGP 110 kV type (Inom=2500 A, Io.nom=40 kA) with a spring drive from Elektroapparat OJSC is shown in fig. 5.

Functioning of high voltage electrical networks in terms of current characteristics, it is not comparable with the operation of household analogues. Accordingly, in the event of an emergency, more powerful devices are needed to shut down the equipment and extinguish the electric arc than standard automatic devices.

As protective structures, SF6 circuit breakers (EC) are used, which can be controlled both in manual mode and with the help of automation. We have described in detail design features and operating principle of the devices. Provided recommendations for installation, connection and maintenance.

SF6 is sulfur hexafluoride, which is classified as an electrical gas. Due to its insulating properties, it is actively used in the manufacture of electrical devices.

In the neutral state, SF6 is a non-flammable, colorless and odorless gas. Compared to air, it can be noted high density(6.7) and molecular weight 5 times the air pressure.

One of the advantages of SF6 is its resistance to external manifestations. It does not change characteristics under any conditions. If decay occurs during an electric discharge, then a full-fledged restoration, necessary for work, soon sets in.

The secret is that SF6 molecules bind electrons and form negative ions. The quality of "electronegation" endowed 6-fluoride sulfur with such a characteristic as electrical strength.

In practice, the electrical strength of air is 2-3 times weaker than the same property of SF6 gas. Among other things, it is fireproof, as it belongs to non-combustible substances, and has a cooling capacity.

When it became necessary to find a gas to extinguish the electric arc, they began to study the properties of SF6 (sulfur hexafluoride), 4-carbon chloride and freon. SF6 won the test

The listed characteristics made SF6 gas the most suitable for use in the electrical field, in particular, in the following devices:

• power transformers operating on the principle of magnetic induction;
• switchgears of complete type;
• high voltage lines linking remote installations;
• high voltage switches.

But some properties of SF6 led to the fact that it was necessary to improve the design of the switch. The main disadvantage concerns the transition of the gaseous phase to the liquid, and this is possible at certain ratios of pressure and temperature parameters.

In order for the equipment to work without interruptions, it is necessary to ensure comfortable conditions. Let us assume that for the operation of SF6 devices at -40º, a pressure of no more than 0.4 MPa and a density of less than 0.03 g/cm³ are required. In practice, if necessary, the gas is heated, which prevents the transition to the liquid phase.

SF6 circuit breaker design

If we compare SF6 devices with analogues of other types, then by design they are closest to oil devices. The difference lies in the filling of the chambers for extinguishing the arc.