As we know,motor protection is one of the important criteria when we involve for AC motor installation,wiring and termination works.Commonly magnetic contactor,fuse, Molded case circuit breaker (MCCB) and overload relays are used for motor control device of induction motor.
In general ideal for motor protection,it have two basic protections always installed for every motor are Over-load protection and Short-circuit protection.For advance protection we can added for protection against unbalanced supply voltages, under voltage, reverse phase, over temperature and stalling etc.
Introduction for AC motor protection
Motor starting current
We should done a proper sizing calculation for fuse overload relay and circuit breaker to suit with starting current for motor protection.During starting,an induction motor can draws 8 to 9 times the full load current depend on what types of motor starter that we used.
This current remain at this high value around 80% of the rated speed of motor.Table below shown some current starting value with different types of starter for our reference and guideline to get ideal sizing for motor protection.
Graph of fuse and overload relay characteristic for motor protection
Types of motor protection device
To ensure our induction motor,wiring and control panel in proper condition when fault or problem happen,we should install a motor protection device including :-
2) Short circuit protection
4) Under Voltage protection
All these topics I’ve explain in a separate post and elaborate detail about protection device one by one for easy understanding and more clear view about motor protection.