Having trouble finding time for training? Check out the how-to videos in EASA’s new series Electric Motor Repair Tips.
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Learn More About Failure Analysis
Are you interested in learning more about how to determine the true cause of an electric motor failure? EASA's Root Cause Failure Analysis manual covers root cause methodology and the specfic stresses that affect each component of an electric motor.
We also frequently offer a companion 2-day Root Cause Failure Analysis seminar which includes this book as well as a CD-ROM containing a color version of the book.
Failures in Three-Phase Stator Windings
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The life of a three-phase stator winding can be shortened dramatically when the motor is exposed to unfavorable operating conditions — electrical, mechanical or environmental. The winding failures illustrated here are typical of what can happen is such circumstances. Failures are shown here to help identify the causes of failure, so that, where possible, preventative measures may be taken.
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 typically caused by contaminants, abrasion, vibration or voltage surge.
Winding shorted turn-to-turn
This type of insulation failure is typically caused by contaminants, abrasion, vibration or voltage surge.
Winding with shorted coil
This type of insulation failure is typically caused by contaminants, abrasion, vibration or voltage surge.
Winding grounded at edge of slot
This type of insulation failure is typically caused by contaminants, abrasion, vibration or voltage surge.
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 damaged 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.
