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Chmki 09

Static motor testing can provide early warnings of potential problems before catastrophic failure occurs. Offline testing involves testing motors above their operating voltages to identify insulation weaknesses, which can indicate issues not detectable during online monitoring. Overvoltage testing methods like surge tests, partial discharge measurements, and direct current high-potential tests are especially useful for finding insulation breakdown early. This allows issues to be addressed proactively through maintenance planning rather than reactively after failure.

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28 views2 pages

Chmki 09

Static motor testing can provide early warnings of potential problems before catastrophic failure occurs. Offline testing involves testing motors above their operating voltages to identify insulation weaknesses, which can indicate issues not detectable during online monitoring. Overvoltage testing methods like surge tests, partial discharge measurements, and direct current high-potential tests are especially useful for finding insulation breakdown early. This allows issues to be addressed proactively through maintenance planning rather than reactively after failure.

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AMITAVA RAY
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Static motor testing can provide warnings of problems before it is too late.

by David Stewart
Electrom Instruments
09/04/2020

Many motor maintenance and reliability programs focus on online testing methods.
In other words, while the motor is running, its temperature, vibration, current and
other conditions are continuously monitored.

Real-time data and alerts can be generated. This is critical information for many
large pump motors, but it is not the only source. Offline testing provides valuable
data that can be incorporated into users’ maintenance and reliability program.  

Offline Testing
Sometimes called static motor testing, offline testing can find insulation weaknesses
by testing above operating voltages.

This provides earlier warning of issues and insulation problems than measurements
taken at operating voltage and enables the owner to keep running the motor while
planning what to do. 

When test voltages exceed the peak operating voltage of the motor, it is known as
overvoltage testing and is the key for finding insulation breakdown early. Overvoltage
testing includes the surge test, partial discharge (PD) measurement and direct
current (DC) high-potential (hipot) test.  
I

MAGE 1: Surge test (Images courtesy of Electrom Instruments)

A surge test is one of the most common motor tests and can find turn-to-turn
insulation weakness in a motor’s windings. If undetected, turn-to-turn insulation
weaknesses will first cause turn-to-turn shorts, then ground wall insulation
breakdown, which causes catastrophic motor failures. During a surge test, voltage
impulses are applied to a winding. This results in decaying waves in each motor
phase and are recorded and displayed by a tester. 

If turn-to-turn insulation damage is present, a wave frequency difference occurs


between the phases or coils being tested.

The difference is calculated as a percent, and failure limits for the percentage
difference can be set (Image 1).  
DC hipot tests provide important information about breakdown of the ground wall
insulation. DC hipot tests include both step voltage and ramp tests that indicate at
which voltage the ground wall insulation starts to break down if there are
weaknesses. 

Predictive Maintenance

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