1) Determine the type and protection form of circuit breaker according to the requirements of line protection-determine whether to choose frame type, device type or current limiting type.

2) The rated voltage UN of the circuit breaker shall be equal to or greater than the rated voltage of the protected line.

3) The rated voltage of the circuit breaker undervoltage release shall be equal to the rated voltage of the protected line.

4) The rated current of the circuit breaker and the rated current of the overcurrent release shall be greater than or equal to the calculated current of the protected line.

5) The limit breaking capacity of the circuit breaker should be greater than the effective value of the maximum short-circuit current of the line.

6) The protection characteristics of the upper and lower circuit breakers in the distribution line should be coordinated, and the protection characteristics of the lower level should be located below the protection characteristics of the higher level and not intersect.

7) The long-delay tripping current of the circuit breaker should be less than the continuous current allowed by the conductor.