How High and Low Voltage Affect Your Motor

When you read about damage to a motor due to voltage variations, you are probably reading about the impact of high voltage. However, both high and low voltages have a significant impact on performance. If left uncorrected, these problems result in premature failure. A slight variation in frequency may not have a major impact. But when the motor experiences a significant change in voltage, the effects can be dramatic.

Impacting Motor Performance

The following are some of the ways that change in voltage impacts performance:

Speed

There is a slight shift in the speed of the motor due to high or low voltage. The amount of speed variation will be directly related to the voltage variation. When the voltage is 110%, the slip increases by about 1%. When the voltage is 90%, slip decreases by approximately 1.5%.

Torque

Torque is mathematically expressed as the square of the voltage. Any variation in voltage, whether high or low, has a significant impact on the maximum and starting torque of the motor. These slight variations become more of a problem when a high load is necessary.

Current

Both full and starting changes in voltage also impact load currents. The starting changes become a problem when the power supply cannot handle a higher starting current.

Efficient Operation

A slight increase in voltage may lead to a small increase in efficiency. Also, a slight decrease in voltage reduces also decreases efficiency. In smaller motors, this might not be a significant problem, but larger motors suffer from efficiency loss.

Overload

It is not uncommon for a motor to experience a temporary increase in load, but if it is operating at a lower than normal voltage, overload results in damage.

Heat

The motor’s heat may increase slightly when it is operating at an increased voltage, but if it is running at a lower voltage, it also experiences a significant rise in temperature. Higher temperatures reduce insulation lifespan and lower the lifetime as well.

In Sum

Regular motor testing as part of a routine maintenance program helps you recognize and correct problems with voltage variation. Paying attention to any voltage variation, however slight, is vital.