How to choose the circuit breaker for motor protection?

Promulgator : TAIXIDate : 2018-08-20Views : 1513

When choosing a circuit breaker to protect the motor, we should pay attention to two characteristics of the motor. One is that it has a certain overload capacity. The other is that its starting current is usually several to ten times the rated current. Therefore, circuit breakers for motor protection can be classified into two categories: one is for protection only and does not bear normal operation; the other is for protection and not frequent operation. In the latter case, operational conditions and electrical life should be considered.

(1) selection principles of circuit breakers for motor protection
① Long delay current setting value = motor rated current.
② Instantaneous setting current. For the circuit breaker of protective cage motor, the instantaneous setting current is 8-15 times the rated current of the motor. The value of the instantaneous setting current depends on the type, capacity and starting conditions of the motor to be protected. For the circuit breaker of the winding rotor motor, the instantaneous setting current is 3-6 times the rated current of the motor. The value depends on the type, capacity and starting conditions of the winding rotor motor.
③ The return time of the 6 times long delay current setting value > the actual starting time of the motor. According to the weight of the load at startup, you can choose a stopover of 1, 3, 5, 8, 15 (s).

(2) The selection of conductor protection circuit breakers for lighting and life use conductor protection circuit breakers refer to the circuit breakers used to protect distribution systems in living buildings. Because the capacity of protected lines is not large, plastic case circuit breakers are often used.
① Long delay setting value < line load current.
② The instantaneous action setting value =6~20 times the circuit load current.

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