Compare a new stator winding (right) with failed windings pictured below.

Winding Single-Phased
(Wye-Connected)

A single-phased winding failure is the result of an open in one phase of the power supply to the motor. The open is usually caused by a blown fuse, an open contactor, a broken power line or bad connections.

Winding Single-Phased
(Delta-Connected)

A single-phased winding failure is the result of an open in one phase of the power supply to the motor. The open is usually caused by a blown fuse, an open contactor, a broken power line or bad connections.

Winding Shorted Phase-to-Phase

This type of insulation failure is usually caused by contaminants, abrasion, vibration or voltage surges.

Winding Shorted Turn-to-Turn

This type of insulation failure is usually caused by contaminants, abrasion, vibration or voltage surges.

Winding With Shorted Coil

This type of insulation failure is usually caused by contaminants, abrasion, vibration or voltage surges.

Winding Grounded At Edge Of Slot

This type of insulation failure is usually caused by contaminants, abrasion, vibration or voltage surges.

Winding Grounded At Edge Of Slot

This type of insulation failure is usually caused by contaminants, abrasion, vibration or voltage surges.

Winding Grounded In The Slot

This type of insulation failure is usually caused by contaminants, abrasion, vibration or voltage surges.

Shorted Connection

This type of insulation failure is usually caused by contaminants, abrasion, vibration or voltage surges.

Phase Damage Due To Unbalanced Voltage

Thermal deterioration of insulation in one phase of the stator winding can result from unequal voltage between phases. Unequal voltages usually are caused by unbalanced loads on the power source, a poor connection at the motor terminal, or a high resistance contact (weak spring).

Note: A one-percent voltage unbalance may result in a six- to ten-percent current unbalance.

Winding Damage Due To Overload

Thermal deterioration of the insulation in all phases of the stator winding typically is caused by load demands exceeding the rating of the motor.

Note: Under-voltage and over-voltage (exceeding NEMA standards) will result in the same type of insulation deterioration.

Damage Caused By Locked Rotor

Severe thermal deterioration of the insulation in all phases of the motor normally is caused by very high currents in the stator winding due to a locked rotor condition. It may also occur as a result of excessive starts or reversals.

Winding Damaged By Voltage Surge

Insulation failures like this are usually caused by voltage surges. Voltage surges are often the result of switching power circuits, lightning strikes, capacitor discharges and solid-state power devices.

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