Circuit breaker is the one of important protection device when installing of electrical induction motor.This time i want shared some information about the major parameter that we need consider when applying Molded case circuit breaker(MCCB) for electric motor.
If we not selected the right MCCB for our electric motor application,it will effected to the system and it not running smooth and achieve our expectation.It will cause a additional costing for upgrading and repairing jobs.
Basically it have three (3) particular for induction motor protection.It is overload,locked rotor and short circuit breaker.This point is very important to ensure our motor protection reliability when problem happen.
Induction motor circuit protection.
1) Overload protection
This protection can avoid the serious damage or malfunction for induction motor if overload happen.We must selected overload protection rated dependent on MCCB and induction motor specification.The protection of induction motors against overheating due to overload, as a result, possibly needs more consideration.
Refer to the International standard for electro-mechanical contactors and motor starters is IEC 947-4-1.From this standard it makes provision for four defined protection trip classes which are directed at overload relays in motor starters.For detail explanation,please refer table below:
2) Locked rotor protection
For locked rotor protection,it is not all MCCB have motor protection capabilities, those manufacturers whose products do have such capabilities, specify both overload and locked rotor protection according to the above trip classes.For more detail please refer to manufacture or electrical consultant.
3) Short circuit protection
This is one more important key that we mus considered when selected MCCB for electrical motor.The estimating value of short circuit current must include with effected connection for induction motor for actual short circuit current value.
It can protect our electrical motor application from serious damage of motor and cable.It also can avoid serious injury for human if failure happen.Normally the short circuit current rated in Kilo ampere unit ( kA )
Assuming that typical induction motors have an internal impedance of about 25%, it is generally accepted that the additional contribution to the short circuit current level is four times the aggregate full load current rating of all connected induction motors.