Why motor require thermal overload protection?

1 Response

  1. Paul says:

    A motor requires thermal overload protection or overload protection is to interrupt the current flow to the motor and protect it from heating damages. Some motors use fuse for short circuit protection and thermal overload protection for overload protection.
    A fuse is a protection device that melts and interrupts the circuit when over current is occurred mainly due to a short circuit. But an overload damages the motor and its parts through a prolonged current flow, this current value will be much lower compared to the current rated for the fuse to blow out. Because in motors the fuse current rating needs to be oversized because the starting current of the motor will be a few times larger (around 3 to 6 times) than the normal current at full speed or operating speed. So, a fuse wire that has a rating to withstand the starting current will not blow for an overload current.

    Overload protection can withstand short over current than normal current but it activates when its temperature is increased. Thermal overload protection will be arranged to heat up proportionally with the motor and its activation temperature will be just near below a margin temperature that is safe to the motor. So, when the current at a high amount of flow for a few long periods the thermal overload also starts to heat and operates. That will prevent the motor from further operating and rising the temperature above its safe operating range.

    Usually, bimetallic strips are used in thermal protection relays, it converts a temperature change into mechanical displacement. Various types of overload protection are available in the market, from a simple strip arrangement to highly sophisticated breakers with advanced features for overload protection.

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