How to choose a suitable circuit breaker?

Select low-voltage circuit breakers according to transformer capacity: 2500KVA, impedance 6﹪, how to choose circuit breakers?

Calculate the rated current of the transformer:

I (rated current) = rated capacity / (rated voltage × √3) = 2500 / (0.4 × √3) = 3623A, you can choose a 4000A circuit breaker

Calculate the short-circuit current of the transformer:

Short-circuit current I = transformer rated current / impedance voltage = 4000A ÷ 0.06 = (maximum short-circuit current) = 67KA, choose a short-circuit segmentation capacity greater than 67KA

Select the P number of the circuit breaker:

TN-C grounding system uses 3P circuit breakers;

TN-C-S, TN-S grounding systems use 4P or 3P circuit breakers;

TT system uses 4P circuit breakers.

Select the type of intelligent control protection for the circuit breaker:

1. Overload long delay protection;

2. Short circuit short delay protection;

3. Short circuit instantaneous protection;

4. Ground fault protection.

5. Installation method of the circuit breaker: fixed and withdrawable.

Generally, the selection is based on the type of switch cabinet. If a fixed circuit breaker is used, an isolating switch should be configured on the incoming line side of the circuit breaker. The selection is based on the functional requirements of the electrical system.