What effect does voltage imbalance have on a three-phase motor?

What effect does voltage imbalance have on a three-phase motor?

• A. Causes overheating and reduced performance due to unequal voltages among phases.
• B. No effect.
• C. Increases torque.
• D. Reduces current draw equally.

Answer: (A)

Voltage balance among the three phases is essential for a steady, efficient rotating magnetic field in a three-phase motor. When the voltages are unequal, the phase currents become unbalanced and the magnetic field is distorted. This distortion causes extra copper losses (I²R heating) in the windings, so the motor runs hotter and less efficiently. The uneven field also reduces the average torque the motor can produce, and can cause vibration and insulation stress if the imbalance is significant. That’s why overheating and reduced performance are the expected outcomes. The other options don’t fit: there is a noticeable effect (not no effect), torque is not increased (it typically decreases or becomes unstable), and currents do not decrease equally—they become unbalanced across the windings.

Voltage balance among the three phases is essential for a steady, efficient rotating magnetic field in a three-phase motor. When the voltages are unequal, the phase currents become unbalanced and the magnetic field is distorted. This distortion causes extra copper losses (I²R heating) in the windings, so the motor runs hotter and less efficiently. The uneven field also reduces the average torque the motor can produce, and can cause vibration and insulation stress if the imbalance is significant. That’s why overheating and reduced performance are the expected outcomes. The other options don’t fit: there is a noticeable effect (not no effect), torque is not increased (it typically decreases or becomes unstable), and currents do not decrease equally—they become unbalanced across the windings.