does it mean we dont need any other short circuit protection measure for motors other than circuit protection ??
Other Types of Motor Protection:
Open-Field Protection:
DC shunt and compound wound motors can be protected against the loss of field excitation by installing field loss relays in the shunt field circuit. Larger Dc mtors may race dangerously with the loss of field excitation, while other motors may not race because of friction and the fact that they are small.
Overspeed Protection:
To prevent damage to driven machine materials in the industrial process or the motor, overspeed protection is provided by controlling the power supply frequency in ac motors and by limiting the maximum shunt field resistance or armature voltage in dc motors. Typical applications included paper and printing plants steel mills processing plants and the textile industry.
Overtravel Protection:
In applications where precise postioning required control devices are used to govrn the starting stpping and reversal of electic motors. these devices can be used to control regular operation or as emergency switches to prevent the improper functioning of machinery.
Overvoltage Proctection:
Devices such as overvoltage relays provide a reduction in the level of applied voltage or maintained interruption of power to the motor circuit when excessive voltage levels are experienced. High induced voltages may occur as a result of the interruption of inductive motor control cicuits.
Reversed Current Protection:
rectifiers are used to protect dc controller in dc or three phase ac systems that can be subject to damage when experiencing phase failures and phase reversals. It is also important to provide reversed currnt protection for battery charging equipment.
Reversed Phase Protection:
Phase failure and phase reversal relays are used to prevent the operation of elevators and industrial machinery to protect motors machines and personnel from ptential hazards when phase revesal or loss occur. Interchanging two phase of the supply of a three phase induction motor will reverse its direction of rotation.
Undervoltage Release:
Undervoltage relays and two wire control are employed to initiate the temporary opening of a motor circuit on the reduction or failure of voltage. On restoration of full voltage the motor is automatically restarted.
For motors with greater than fractional horsepower ratings devices such as fuses circut breakers and selfprotected combination controllers must be installed ahead of the motor control apparatus to protect branch circuit conductors, motor control apparatus personneel and the motor itself against fault conditions that may be the result of shortcircuits or grounds.