SF6 Electric Circuit Breakers: Operating Principle

The method of arc quenching with a variety of gas mixtures has long been known both in scientific physics and in the production process. Modern equipment with prepared gas SF-6 inside is widely used for industrial purposes to prevent accidents. But what exactly are the processes that take place at this moment in the device itself, is not known to everyone. Therefore, below we will consider the principles on which such a device as a gas-insulated switch is based.

Design Features

An elegas circuit breaker is a device designed to control and supervise high and medium voltage power grids. It is similar in construction to an oil circuit breaker, but instead of an oil mixture, there is gas inside. Also, this comparison shows that the gas-insulated unit is much more durable and requires less maintenance. Usually sulfur is used as a gas, but other mixtures also exist.There are the following types of designs:

• rotary;
• air;
• longitudinal.

Principle of operation and application

The operation of the device is based on the phase isolation method of using an electrogas. In detail, the principle of the column switch is as follows:

• The arrival of the tripping signal causes the chamber signals to open.
• The built-in contacts of the device then create an arc.
• The medium with the activated arc causes the gas to actively divide into particles.
• The high pressure caused by this process, reduces the quality conductivity of the medium itself and the arc goes out.
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In some designs, a separate compressor is provided to help pressurize the situation in low-pressure devices. Also, gas blasting uses bypassing, which equalizes the amperage and stabilizes the process.



The operating principles of the column devices are somewhat different:

• The device is controlled by transformers and auxiliary drives. This approach provides the ability to hold the arc within a certain power, as well as controlled switching off and on of the entire network;
• The actuators themselves can be hydraulic or spring-loaded. Purely spring actuators are based entirely on mechanical joints, so they are structurally simple and reliable. Hydraulic actuators are a hydraulically augmented version of the spring mechanism.

The hydraulic system is more reliable due to the hydraulic insurance, but it is burdened with the risks associated with the same.

Advantages and disadvantages

Any mechanism or device has a number of advantages and disadvantages.

In our case, the former include:

1. Versatility - voltages that the device cannot handle simply do not exist.
2. Speed - the response speed of an SF6 is measured in thousands of seconds, which allows you to make an emergency shutdown in a really short time.
3. Fire safety and resistance to vibration.
4. Service life - the body of the device is reliably protected, and contacts protected by gas medium are not subject to wear and tear in principle.
5. Functionality in high-voltage networks - the same vacuum devices cannot do that.

This is where the best features of this switch end, so let's move on to the disadvantages:

1. Price - the gas-insulated mixture itself is expensive, and the work to create the device is quite costly, so this switch is quite expensive.
2. Low temperatures - the biggest disadvantage of this device. The device is basically not able to work at low temperatures, because they strongly affect the physical properties of the contents, disrupting the performance of the entire system.
3. Expensive maintenance - repair work on devices of this type is quite rare. Its design features help it to remain reliable almost always, but if repair is necessary - it will be very expensive. First, to make such repairs can only high-precision equipment, which in itself is rare, and secondly, the specialists who know how to handle this equipment, also ask for a high fee.
4. Expensive installation - the situation is completely similar to maintenance. Installation is extremely difficult to perform, because the work on the preparation of a special platform can only be done by a professional.

Finally

We hope that now there are no gaps for you in the theoretical principles of high-voltage gas-insulated circuit breakers.