Supply voltage effects on the operation
The existing load is a major factor in determining how much of a decrease in supply voltage a motor can handle see sidebar, below. May 01, The economic loss from premature motor failure is devastating.
What happens if an induction motor runs below its rated voltage?
However, extremes above the design voltage will cause the amperage to go up with a corresponding increase in heating and a shortening of motor life. On lightly loaded motors with easy-to-start loads, reducing the voltage will not have any appreciable effect, except that it might help reduce the light load losses and improve the efficiency under this condition. An assumption people often make is that since low voltage increases the amperage draw on motors, then high voltage must reduce the amperage draw and heating of the motor. This would not damage the motor, if the current stays below the nameplate value. Thus, high voltage can shorten motor life even on lightly loaded motors. When amps go above the nameplate rating, heat begins to build up in the motor. Thus, when voltage gets low, the current must increase to provide the same amount of power. For example, let's look at a motor that carries a light load. Don't place stress on your electric motors and other electrical equipment as a result of operating a power system at or near the ends of voltage limits. You may even be close to the nameplate's lower limit for voltage. Thus, the voltage range they can tolerate on the high-voltage connections is V to V. This is also true of ballasts in fluorescent, mercury, and high-pressure sodium light fixtures. In this case, you already have a high current draw, so voltage is already lower than it would be without the load. On some motors, it might occur at a point below rated voltage.
However, extremes above the design voltage will cause the amperage to go up with a corresponding increase in heating and a shortening of motor life. Voltage drop is a static figure that is a function of wire resistance.
Running ac motor at lower voltage
Don't fall into the trap of thinking you're okay just because your supply voltage falls within these tolerance bands. In most cases, the price of the motor itself is trivial compared to the cost of unscheduled shutdowns of processes. Thus, the voltage range they can tolerate on the high-voltage connections is V to V. Similarly, the motor's pullout torque would be much lower than it would be under normal voltage conditions. Design The Highs and Lows of Motor Voltage Operating a motor at the outer limits of its voltage requirements reduces its efficiency and causes premature failure. This is not the case. This is also true of ballasts in fluorescent, mercury, and high-pressure sodium light fixtures.
But, it's only representative and does not give precise information that applies to all motors. Also, the rise in full load amps at voltages above rated tends to be steeper for some motor winding designs than others. Both high and low voltages can cause premature motor failure, as will voltage imbalance.
Operation on a continuous basis at either the high or low extreme will shorten the life of the motor. The starting torque, pull-up torque, and pullout torque of induction motors all change, based on the applied voltage squared.
When you have a voltage reduction, the current would rise to a new value, which may exceed the full-load rated amps.
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