How to choose suitable circuit breaker
2019-08-31 15:12:00
1. Selection of distribution circuit breakers. The distribution circuit breaker is generally used in the low-voltage power grid for the distribution of electrical energy, including the main power circuit breaker and the load branch circuit breaker. When selecting this type of circuit breaker, special attention shall be paid to the following selection principles: the allowable current carrying capacity of (1) line shall not be less than the setting value of the long time-delay action current of the circuit breaker. If wire and cable are used, the setting value of long-time action current of circuit breaker can be 80% of the allowable carrying capacity of wire and cable. 2) The starting time of the motor with * large starting current in the line shall not be greater than the returnable time of the setting value of the action current with 3 times of the long time delay. 3) Instantaneous current setting value I1: I1 = 1.1 (ijx + klkiedm). KL is the impact coefficient of the starting current of the motor, generally KL = 1.7-2; IEDM is the rated current of a large motor.
2. Selection of motor protection type circuit breaker. The motor has two characteristics: one is that the starting current is usually several times of the rated current; the other is that it has certain overload capacity. Therefore, when choosing the circuit breaker to protect the motor, we must pay attention to these two characteristics of the motor. In order to ensure the reliable operation of the motor, we should pay attention to the following points when choosing the circuit breaker:
(1) The setting value of the long time delay action current of the circuit breaker is determined by the rated current of the motor.
(2) The returnable time of the setting value of the 6 times long time-delay action current of the circuit breaker is greater than the actual starting time of the motor.
(3) Setting value of instantaneous action current of circuit breaker: cage motor shall be 8-15 times of rated current of tripper; winding motor shall be 3-6 times of rated current of tripper.
3. Selection of household protective circuit breaker. In the home power supply, the circuit breaker is usually used as the main power protection switch or branch line protection switch. In case of short circuit or overload of lines or household appliances, the circuit breaker can trip automatically and cut off the power supply, so as to effectively protect these equipment from damage and reduce the accident to a small range. Generally, single pole (1P) is used as branch protection and two pole (2P) circuit breaker is used as main power protection. It is very important to choose the rated capacity current of the circuit breaker in the family, because if the rated current of the circuit breaker is too large, the circuit breaker cannot trip automatically and cut off the power supply when the circuit or household appliances are short circuited or overloaded. If the selected circuit breaker is too small, it is easy to trip frequently, causing unnecessary power failure, affecting normal life and causing unnecessary trouble.
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