TYPICALCAUSES

OFWINDINGFAILURES

INTHREE-PHASEMOTORS

Typical causes of winding failures in three-phase motors are poor operating conditions-environmental, electrical, or mechanical-can dramatically shorten the life of your three-phase stator windings. The failures types listed below are typical of what can happen in these situations. We show them here to help you identify the causes of failure, so that you may take preventive measures.

Correcting your POWER FACTOR will add years to your motors life. Read Power Factor REPORT.

Winding Single-Phased (Wye-Connected)

A single-phased motor 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 motor 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 motor insulation failure is usually caused by contaminants, abrasion, vibration or voltage surges.  

Winding Shorted Turn-to-Turn

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

Winding With Shorted Coil

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

Winding Grounded at Edge of Slot

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

Winding Grounded at Edge of Slot

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

Winding Grounded In the Slot

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

Shorted Connection

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

Phase Damage Due To Unbalanced Voltage

Thermal deterioration of motor insulation in one phase of the stator winding can result from unequal voltage between phases. Unequal voltages are usually 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 motor current unbalance. 

Winding Damage Due To Overload

Thermal deterioration of the motor 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 motor insulation deterioration. 

Damage Caused by Locked Rotor

Severe thermal deterioration of the motor 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

Motor 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.