Which statement best describes the relationship of windings resistance in a healthy three-phase motor?

Which statement best describes the relationship of windings resistance in a healthy three-phase motor?

• A. All windings have the same resistance
• B. The run winding has lower resistance than the start winding
• C. The winding-to-ground resistance is the same as winding-to-winding
• D. The resistance varies randomly

Answer: (A)

In a healthy three-phase motor, the three stator windings are designed to be identical so their impedances are equal. When each winding has the same resistance, the three phase currents are the same under the same line voltage, keeping the magnetic fields balanced. This balance produces a smooth rotating field and even torque. If any winding had more resistance, it would carry less current, creating an imbalance that leads to uneven torque, extra heat, and vibrations. The idea of a distinct start winding with lower resistance doesn’t apply to a standard three-phase motor, since all windings should be matched. Winding-to-ground resistance is about insulation and is normally much higher and not the same as winding-to-winding impedance, and resistance varying randomly would indicate a fault. So equal winding resistance across all windings best describes a healthy motor.

In a healthy three-phase motor, the three stator windings are designed to be identical so their impedances are equal. When each winding has the same resistance, the three phase currents are the same under the same line voltage, keeping the magnetic fields balanced. This balance produces a smooth rotating field and even torque. If any winding had more resistance, it would carry less current, creating an imbalance that leads to uneven torque, extra heat, and vibrations. The idea of a distinct start winding with lower resistance doesn’t apply to a standard three-phase motor, since all windings should be matched. Winding-to-ground resistance is about insulation and is normally much higher and not the same as winding-to-winding impedance, and resistance varying randomly would indicate a fault. So equal winding resistance across all windings best describes a healthy motor.