The functioning of high-voltage electrical networks for current characteristics is not comparable with the work of household counterparts. Accordingly, in the event of an emergency, more powerful devices than standard automatic devices are necessary to turn off the equipment and extinguish the electric arc.
As protective structures, gas-insulated breakers (EF) are used, which can be controlled both in manual mode and with the help of automation. We described in detail the design features and the principle of operation of the devices. Gave recommendations for installation, connection and maintenance.
The content of the article:
- Determination and application of SF6 gas
-
SF6 circuit breaker design
- Kolonkovye and tank devices
- Arc extinction principle
- What is the drive for?
- Advantages and disadvantages of using EV
- Rules of connection and maintenance of EV
- Conclusions and useful video on the topic
Determination and application of SF6 gas
Sulfur hexafluoride 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 gas is a non-combustible gas with no color or odor. If we compare it with air, we can note a high density (6.7) and a molecular weight that is 5 times the air mass.
One of the advantages of SF6 gas is resistance to external manifestations. It does not change the characteristics under any conditions. If a decay occurs during an electrical discharge, then a full-fledged restoration is necessary.
The secret is that the SF6 molecules bind electrons and form negative ions. The quality of “electronegatives” gave 6-fluoride sulfur a characteristic such as dielectric strength.
In practice, the electric strength of air is 2-3 times weaker than the same property of SF6 gas. Among other things, it is fireproof, as it refers to non-combustible substances, and has a cooling capacity.
When it became necessary to find a gas for extinguishing electric arcs, they began to study the properties of SF6 (sulfur hexafluoride), 4-chloride carbon and freon. SF6 won in trials
The listed characteristics have made SF6 the most suitable for use in the electrotechnical sphere, in particular, in the following devices:
- power transformers operating on the principle of magnetic induction;
- switchgears of the complete type;
- high voltage lines connecting remote installations;
- high voltage switches.
But some properties of the SF6 gas led to the need to improve the design of the switch. The main disadvantage concerns the transition of the gaseous phase to the liquid, and this is possible with certain ratios of the parameters of pressure and temperature.
That the equipment worked without interruptions, it is necessary to provide comfortable conditions. Suppose for the operation of gas-insulated devices at -40 º, a pressure of no more than 0.4 MPa and a density of less than 0.03 g / cm ³ are necessary. In practice, if necessary, the gas is heated, which prevents the transition to the liquid phase.
SF6 circuit breaker design
If to compare gas-insulated devices with analogues of other types, then by design they are closest to oil devices. The difference is in filling the arc extinguishing chambers.
As a filler for oil switches an oil mixture is used, and in gas-insulated ones - 6-fluoric sulfur. The advantage of the second option in durability and minimum maintenance.
Diagram of the gas-insulated core type device. The arcing modules mounted on a high rack are in the upper part, the control cabinet is in the lower
The ways of extinguishing the electric arc depend on many factors, among which the rated current and voltage, as well as the conditions for using the device, are decisive.
In total, there are four types of EV:
- with electromagnetic blast;
- with blast in gas - with 1 stage of pressure;
- with longitudinal blowing - with 2 pressure levels;
- with autogenerated blast.
If in air devices in the process of extinguishing the arc the gas enters the atmosphere, then in gas-insulated gas it remains in a confined space filled with a gas mixture. This maintains a slight overpressure.
Kolonkovye and tank devices
In practice, there are two types of gas-insulated installations:
- tank;
- kolonkovye.
The differences relate to both structural features and the principle of electric arc extinction. According to the external device, the core ones resemble low-oil analogs: they consist of two functional parts - arcing and contact parts; they have the same volumetric dimensions.
Disconnecting devices are designed to operate from 220 V and belong to the single-phase equipment. An example of an insulated gas circuit breaker is LF 10 Schneider Electric.
The equipment can be controlled in two different ways: manually, when adjustment and control are carried out using mechanical devices, and remotely, automatically
Gas-insulated gas appliances are smaller and equipped with a multi-phase drive. This distribution allows you to better control and smoothly adjust the voltage parameters.
One of the advantages of tank EVs is the ability to withstand increased loads. This quality is ensured by a current transformer embedded in the design.
An example of a tank device is the DT2-550 F3 Alstom Grid gas-insulated installation. Such devices have positively proven themselves in electrical systems with a voltage of 500 kV.
The design is assembled and equipped in such a way that it functions without failures at low temperatures. (critical), high humidity, as well as in regions with seismic activity and excess pollution of the atmosphere.
Arc extinction principle
How the device works, consider the example of the switch LW36 Chinese manufacturer CHINT.
When disconnected, the spring acts on the dynamic elements of the cylinder, and they fall down. All contacts, except for arc-suppressing, open. When the arcing contacts are disconnected, through which the current flows, an electric arc arises.
Hot gas moves to the heat chamber, the check valve is activated. When gas from the heat chamber is blown into the gap, the arc is extinguished.
If small currents are disconnected, then the pressure in the heat chamber is insufficient, therefore the pressure from the compression chamber is attracted (it is always higher). The check valve opens, the gas flows freely into the gap and extinguishes the arc when passing through zero.
Diagram of the internal arrangement and operation of mobile, fixed valves, decompression, check valves. Position 1 - inclusion; position 2 - disable large currents; position 3 - off small currents; position 4 - turn off the device
Modern kolonkovy installations possess the improved characteristics. Maintenance is reduced to a minimum, the switching resource is increased. Gas-insulated switches are notable for low noise level, reliable mechanics, ease of installation and test work.
Adjustment of tank models is made with the help of a drive and transformers. The spring or spring-hydraulic drive controls the on / off processes, the level of electric arc retention.
What is the drive for?
The drive is designed to perform all operations associated with switching on / off or holding the unit in a certain position. The diagram shows exactly where the drive can be located. Usually this is the ground surface or a low support, providing service personnel with easy access to control devices.
The design of the tank switch: 1 - porcelain or polymer modules; 2 - transformers; 3 - tank with gas extinguishing device; 4 - chamber with gas; 5 - hydraulic type drive; 6 - metal frame; 7 - connector for SF6 gas injection
The drive consists of the switching mechanism, the locking device - the latch, the tripping mechanism. The process of switching on should take place as quickly as possible in order to avoid welding of contacts.
During the start-up, great efforts are made to overcome the frictional force of all the elements involved. Disconnection is made easier and consists in the reverse movement of the latch, which ensures the inclusion and retention.
There are several ways to enable / disable:
- mechanical;
- spring;
- cargo;
- pneumatic;
- electromagnetic.
For low-power systems use manual control. In this case, the strength of one operator is sufficient. Turning off manual mechanisms is usually carried out in automatic mode. The spring drive is also manually actuated, but low-powered electric motors are sometimes involved.
The traditional location of the drive - about the mounting metal frame. The integrity and functioning of the mechanism provides a durable metal casing - a box with a convenient door for camera work
To use an electromagnetic drive, more energy is required, therefore a constant current source of approximately 58 A with a voltage of 220 V is needed. There is a manual lever as a backup mechanism. Electromagnetic devices are reliable, therefore they are successfully exploited in areas with severe winters. Minus - the need for a powerful battery.
Pneumatic drive is different in that instead of an electromagnet, the main working element is a cylinder / piston pair. Thanks to compressed air, the switching speed is much higher than that of previous models.
Advantages and disadvantages of using EV
Gas-insulated circuit breakers, like other types of electrical switchgear, have a number of advantages and disadvantages. When choosing an installation, the necessary calculations are made and, in addition to technical characteristics and design features, take into account the pros and cons of the models.
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Gas-insulated circuit breakers are versatile - they are used regardless of the mains voltage
To extinguish the electric arc in case of an emergency, the gas-insulated device requires a fraction of a second
All parts of the installation are able to work without repair for decades, and SF6 gas does not require regular replacement.
Gas-insulated arcing devices easily cope with the disconnection of high-voltage systems. For comparison - vacuum analogues do not withstand high voltage
Universal application in high-voltage systems
Efficiency of performance of working functions
Reliability and durability
Work with high voltage current
Gas-insulated switches operate in difficult conditions with periodic vibrations, low temperatures (heated), in fire-hazardous areas.
The disadvantages include the high cost of the filler - SF6 gas, the specificity of mounting on a shield or foundation, the need for a certain qualification of the operating personnel.
Rules of connection and maintenance of EV
All actions relating to the installation, on / off, repair and maintenance of gas-insulated devices are subject to strict rules that are regulated by the OLC 1.8.21.
To connect the installation, it is necessary to check the presence of the minimum pressure in the gas-filled chamber, otherwise the switch will fail. To prevent damage, an alarm has been set up, which is triggered when a critical decrease in pressure parameters. The pressure level can be monitored using a pressure gauge.
In the drive cabinet, heating elements are installed that effectively prevent the formation of condensate on the elements of the mechanism. The operator must ensure that the heaters are always on.
Inspection of the installation is done every day in the daytime and about 2 times a month in the dark. If an emergency shutdown occurs due to one of the reasons, an unscheduled inspection is required.
During the inspection of the circuit breaker, it is necessary to check the external protection, remove contamination, repair damage. If the contacts heat up, you should find out the reason.
If there is cod, suspicious noise needs to be identified. The metal mounting structure is also part of ground looptherefore, its integrity should be checked.
Be sure to remove the indicators of the gauge. Pressure should according to the rate calculated by the manufacturer. It is necessary to check the serviceability of the regulating and control devices, and if one or several elements fail, take steps to make a replacement or send it in for repair.
If the gas pressure has decreased, refill the chamber with SF6 gas. Insulation does not need cleaning, as the design is completely sealed.
Conclusions and useful video on the topic
How the gas-insulated circuit breakers are arranged, what is the principle of arc extinction and what types of devices there are, you can learn from the useful and informative video.
Video # 1. Overview of gas-insulated circuit breakers with a description of the device and the principle of operation:
Video # 2. Design features of installations:
Video # 3. How to install the switch:
Gas-insulated switches leave the factory conveyor in full operational readiness and are designed to work in various climatic zones, from tropical to cold, therefore they are actively used by industrial companies of various countries.
