How to design an induction motor for wide voltage fluctuation?

In villages sometimes we have to face this problem of voltage fluctuations...normally we design induction motor (single phase) for 230 volts rated. So it can work satisfactorily for 200 volts to 240 volts range but due to some reasons our supply may give us 150-160 volts so in that case induction motor draws more current which causes i^2 R LOSSES, consequently heating so we want to get rid of this problem by doing any modification in motor (stator winding).

The voltage variation from 140 volts to 240 volts is a very large variation of about 26% in a base average voltage of 190 volts. It is normal for Utility power sources to fluctuate plus or minus 5% to an extreme of plus or minus 10%. This can be taken care of by equipment with automatic voltage regulators or with automatic on-load tap changers on large power transformers but the voltage variations of 26% for induction motors is extraordinarily high. For electronic and digital equipment (smaller wattage like computers) voltage variations can be corrected by solid state circuits but for induction motors especially larger motors, your automatic voltage regulator may involve a bigger and expensive AVR units.
Induction motor
Another factor is the winding current capacity of your induction motor. The winding conductors shall be oversized for the lower voltage in order to carry the higher current when the motor is operating at the lower voltage of 140 volts.

The voltage drop problem in the village is mainly the problem of your Electrical Utility provider. Your community has to bring this problem to the attention of the Electric Utility provider so that they can install some voltage correction devices at the remote end of the primary distribution lines. Economical solutions may be installing some automatically switched capacitor banks at the end of the primary distribution lines. More expensive solution is adding automatic voltage regulators at the feeder primary distribution circuits. Your Electric utility provider should also make an audit of the existing tap settings of your distribution transformers and then make corrective changes at the field after they make a load survey of the voltage profile in the areas having such problems.

Another way you may better find the more output power to replace the current one (more than your load point around 25%), that case of the lower voltage drop lower than 200v the motor still driving to survive the power drive to load and heating on the wind should be satisfy, this way better than you buy another control device which are increasing the cost to your system.

Motor installations require overload protection (normally thermal overload relays) in order to protect the induction motor windings from overheating. This overload protection is provided in addition to the motor short circuit protection (usually circuit breaker or fuse). The setting of the motor overload protection is about 1.12 to 1.2 times the full load current of the induction motor. When the applied voltage to the terminals of the motor drops too low than the normally rated operating voltage of the motor, the current draw of the induction motor will rise. If the rise is over the overload protection setting, the overload relay will trip in order to protect the motor winding from overheating.

Leave your comment


12/21/2016 11:37 AM
Dear Sir/Madam

I have 100hp induction motor and 250W mercury vapour lamp, when motor run on full load, voltage suddenly drops and light got off, plz give any solution??