Internal accessories of circuit breakers

The distribution (line), circuit breakers for overcurrent protection of motor and household appliances, due to the protection of objects (such as transformer, wire and cable, motor and household appliances, etc.) of the overload current capacity (including motor starting current and starting time) there are differences, protection characteristics of circuit breaker with different selection.

1 the selection of common short circuit

1.1 selection of circuit breakers for distribution

Breaker is a circuit breaker which is specially used for distributing electric energy in low voltage power network, including power circuit breaker and load circuit breaker. When choosing this type of circuit breaker, pay special attention to the following selection principle:

(1) the current setting value of the long time delay action current of the circuit breaker, the allowable load capacity. For the case of wire and cable, it is desirable to allow the flow of wire and cable 80%.

(2) the starting time of the motor with the maximum starting current in the return time line of the 3 times long delay action current setting value.

(3) short delay action current setting value I1:

I1=1.1 (Ijx+1.35kIed)

Load current (A) calculated by Ijx line;

Starting current ratio of K motor;

Ied motor rated current (A).

(4) instantaneous current setting value I2:

I2=1.1 (Ijx+klkIedm)

Formula: KL motor starting current of the impact coefficient, generally take kl=1.7 ~ 2;

Iedm maximum rated current of an electric motor.

(5) the short delay time stage, according to the power distribution system. The general time period is 2 ~ 3. The short delay time difference between each stage is 0.1 ~ 0.2S, the action precision of the short delay mechanism of the circuit breaker is decided, and the return time should ensure the selective action at all levels. After selecting the short delay step, it is best to check the thermal stability of the object to be protected.