Circuit-breaker: description, purpose

The SF6 circuit breaker is a switching device, which is widely used in electrical installations with a voltage class from 6 to 220 kV. As an arc-breaking and insulating medium of the device is an electric gas (SF6 gas). It is a chemically inactive, harmless, non-flammable gas that has excellent thermal conductivity and electrical strength. The advantages of electric gas include the fact that it does not require care as a transformer oil, does not exert a destructive effect on the design of the apparatus (under normal operation), does not age, and, in addition, is relatively inexpensive.

The SF6-circuit-breaker has an arc-extinguishing device, which is characterized by simplicity of construction, as well as small overall dimensions. The arc is extinguished with an insignificant number of discontinuities and quite quickly. Now we will consider, by what principle the arc is quenched in the apparatus and its design features. The SF6 switch has three poles. Each of them is a metal hermetic reservoir, which is filled with compressed gas at a pressure of 0.6 MPa. In each pole there is an auto-pneumatic device designed to extinguish the arc.

Advantages of SF6 circuit breakers:

- possibility of operation in electrical installations of open and closed execution of all voltage classes;

- Reliability and simplicity of design;

- large switching resource of the contact system;

- good breaking capacity;

- high level of operation;

- fire and explosion safety;

- small weight and overall dimensions.

Switch The SF6 gas has several disadvantages:

- high requirements to the quality of electric gas;

- use of special equipment, which is necessary for periodic maintenance of switching devices;

- in the process of operation of the device harmful substances are formed for the human body - fluorides.

However, despite these shortcomings, switches of this type create serious competition to oil and air switching devices.

SF6-type devices are designed for operation in very difficult weather and natural conditions. For example, 110 kV SF6 circuit breakers are capable of operating at an ambient temperature of -35 to +40 degrees Celsius, can be installed at an altitude of more than 1,000 meters above sea level. During the operation of such devices, the shutdown and switch-on cycles are performed. When the circuit breaker is operated within the nominal current value (2000 A), it is able to perform a shutdown operation 6000 times, and in the emergency mode, a short-circuit current generally passes through it, and the device is only able to perform 400 shutdown cycles. The gas-insulated switch (35 kV) has a rated current greater than that of the apparatus rated at 110 kV, it is 3150 A, and the rated breaking current is 50 kA. These devices are designed for the largest peak of the trip - 127.5 kA.

In conclusion, we add that air and oil switches gradually give way to SF6 and vacuum switching devices. This can be explained by the excellent arc-breaking characteristics of SF6 and vacuum, and also by the increased operational safety of such equipment.