How does the unbalanced voltages cause the motor windings temperature to rise?
A – During periods of moderately unbalanced voltages, the motor will draw more current without increasing its output torque. This extra energy is converted to captive heat within the windings. Operating at normal speeds, a small percentage voltage unbalance will result in a much larger current unbalance. In most cases, the current unbalance percentage will be 6 to 10 times the voltage unbalance percentage. A 2% voltage unbalance can mean a current unbalance of 12 to 20%; therefore, a very small increase in voltage unbalance will create a large increase in the motor’s winding temperature. THE PERCENTAGE OF OVERHEATING in the motor windings can be calculated directly if the percentage voltage unbalance is known. (See Graph Below).
