(1) Switching appliance: mainly used to close the normal circuit and the accident circuit or to isolate the high-voltage power supply, according to its different functions are divided into:

1) High-voltage circuit breaker: it can break a variety of load circuits under normal circumstances, and can close and break short circuit current in an accident, and can realize the requirements of automatic reclosing. It is one of the most comprehensive electrical appliances in high voltage circuits.

2) High-voltage fuse: commonly known as insurance, when the current in the line exceeds a certain limit or there is a short circuit, it can automatically disconnect the circuit, after the circuit is disconnected, the fuse must be manually replaced before it can be used again.

3) High-voltage load switch: it can only close and break various load circuits under normal working conditions, but can not break short-circuit current.

4) High voltage isolation switch: used to isolate the power supply or circuit, the isolation switch can only break a small current, the capacity of the transformer no-load current and so on.

5) Ground switch: In order to ensure personal safety when overhauling electrical equipment for high-voltage and ultra-high-voltage lines, the ground switch can be grounded, and the ground switch can also be artificially caused by the grounding short circuit of the power system to achieve the purpose of control and protection.

(2) Measuring electrical appliances: mainly including current transformers and voltage transformers.

1) Current transformer: used to measure the current of high-voltage lines for measurement and relay protection.

2) Voltage transformer: used to measure the voltage of high-voltage lines for measurement and relay protection.

(3) Current limiting and voltage limiting appliances: mainly including lightning arrester, reactor.

1. Lightning arrester: used to limit overvoltage, so that the power system related electrical equipment from atmospheric overvoltage and internal overvoltage harm.

2. Reactor: Essentially an inductance coil, used to limit the short-circuit current in case of failure. What are the basic requirements for high voltage appliances: What are the performance parameters? The main requirements of high voltage appliances include: general electrical performance requirements, natural environment requirements, and other requirements. General electrical performance requirements: the high-voltage electrical appliances in the power system should be able to withstand various voltages and currents for a long time without damage.

1) Voltage: High voltage appliances with a certain rated voltage, the insulated part of which can withstand the maximum working voltage for a long time, and can withstand the corresponding degree of atmospheric overvoltage and internal overvoltage. The performance parameters in this aspect are: maximum operating voltage, power frequency test voltage, full wave and carrier impulse voltage, operating wave test voltage.

2) Current: When the conductive part of the high-voltage electrical appliance passes the working current for a long time, the temperature rise of each part does not exceed the allowable value. When passing the short-circuit current, it should not be damaged by the electrodynamic action, the temperature rise of each part should not exceed the allowable temperature value during the short circuit, and the contact should not be welded or damaged. These properties are related to the size of the current, and the parameters that mark this aspect are: rated current, dynamic stable current, thermal stable current, etc.