Why is it that variation allowed in supply voltage to
motors is (+ or -)10 %, whereas that in frequency is (+ or -
)5 %

Answer Posted / gajendran.al

Variation in supply voltage to motor affects the torque
produced by the motor and is not affected much with +/- 10%
whereas variation in frequency affects the speed of the
motor. Even 1Hz variation could vary speed by 30 rpm for a
4 pole motor. So variation in frequency is not advisable in
motor
Pl note that increase in supply frequency makes the motor
rotate above rated speed which may cause mechanical failure
of motor.

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