Voltage sag: It is usually associated with system faults but can also be caused by energization of heavy loads or starting of large motors. Voltage sag is the short reduction in the RMS voltage between 0.1 to 0.9 pu for a duration of 0.5 cycle to 1 minute
Let, E→EMF in volt φ→Flux in weber A→Parallel path (for wave winding = 2) Z→No. of armature conductors N→speed in rpm P = Number of poles E = PφNZ/(60A) E = 8*0.020*625/(60*2) E = 500 V