Static, Dynamic and Reactive Force for Electric Motors

The electrical machine what you are referring can be operated as motor by giving supply to its terminal and as generator by driving it by a prime mover. Under normal operating condition either as motor or as generator, stator body experiences a torque corresponding to its rating, speed etc. This is the continuous unidirectional torque that would be experienced by the machine.

In case of line to line fault, when working as generator, extra fault current would be flowing through the stator winding. ( in case of motor if the fault is at its terminal then motor would not get its input power and would stop as single healthy phase would bot be able to generate required torque.) This extra fault current flowing in the generator would generate a pulsating torque which will add to the normal load torque in half cycle and subtract and other half cycle. Therefore while specifying torque after normal load torque plus and minus sign is used there by indicating that this torque due to line to line fault is of pulsating nature and would add and subtract during the cycle. This pulsating torque is controlled by various (positive, negative and zero sequence) reactances of various components of source and other components.

Thank you Mr. pcchatur for your reply.

What is the deciding criterion for this short-circuit level.

Pl. clarify.

DHAYANANDHAN.S