1. Selection of switchgear: high-voltage circuit breaker (rated voltage, rated current, rated breaking current, rated closing current, thermal

stability current, dynamic stability current, opening time, closing time)

Specific problems of the breaking capacity of high-voltage circuit breaker (the effective breaking capacity is the short-circuit current of the

actual breaking time; the DC and AC components of the rated short-circuit breaking current; the breaking coefficient of the prime minister;

the reclosing; the breaking capacity under special circumstances)

Disconnecting switch: used to isolate power supply, switch damage, and open and close small current circuit

High voltage fuse: working principle; Technical characteristics and technical parameters (the greater the current flowing on the melt, the

faster the fuse will fuse; the rated current of the fuse, the rated current of the melt, and the maximum breaking current, that is, the capacity);

Divided into current-limiting and non-current-limiting high-voltage fuses; Determine the rated voltage and rated current according to the

equipment protected; The rated breaking current determines the current-limiting type and non-current-limiting type; Selective efficacy

High-voltage load switch: it can break normal load current and overload current, and can also close certain short circuit current, but it cannot

break short circuit current. Therefore, it is usually used together with fuse.

2. Selection of current transformer: basic requirements (thermal stability and dynamic stability); Current transformer for measurement (type,

rated parameters, accuracy level, secondary load, performance calculation); Current transformer for protection (type, rated parameters, accuracy

level, secondary load, steady-state performance of P-level and PR level current transformer and transient performance of TP level current

transformer in performance calculation)

3. Selection of voltage transformer: general provisions for selection (type and wiring selection; secondary winding, rated voltage, accuracy class and

error limit); Performance calculation (secondary load calculation, secondary circuit voltage drop)

4. Selection of current-limiting reactor: its function is to limit short-circuit current; Bus reactor, line reactor and transformer circuit reactor; It is

classified as common current-limiting reactor and split reactor; The reactor has no overload capacity, and the rated current is considered as the

maximum possible current at any time; Limit the short-circuit current to the required value to determine the reactance percentage; The common

reactor and split reactor are verified by voltage fluctuation.

5. Selection of shunt reactor: absorb capacitive reactive power of cable; Connected in parallel to the EHV line; Selection of compensation capacity

6. Selection of series reactor: limit inrush current (0.1% – 1% of reactance rate); Harmonic suppression (reactance rate 5% and 12% mixed)