Hi-Pot Testing AC Motors - What You Need to Know
Every now and again, a customer will ask us if they can (or should) perform a Hi-Pot test on their AC motor. Here are a few things that every motor end user, motor shop and OEM should be aware of when it comes to Hi-Pot Testing their motors.
What is Hi-Pot Testing?
Hi-Pot is short for High Potential, i.e. high voltage. High Potential Insulation Tests, also known as Dielectric Withstand Tests, are used to check the integrity of a motor’s insulation, and establish whether it can withstand a high potential without risk of failure. By its nature, the Hi-Pot test can be very destructive, and can kill a motor if incorrectly processed. Weak insulation can cause failure during the test itself.
When are Hi-Pot Tests done?
All new Elektrim Motors are Hi-Pot tested at the factory during routine testing for 1 minute at the full voltage (1000V + twice the rated nameplate voltage). For example, a 460V motor is Hi-Pot tested at the factory at a full voltage of 1920V, i.e. ((2 x 460V) + 1000V). This is done to uncover any weakness in the windings. This testing ensures that every motor that leaves our factory is proven to have good insulation strength BEFORE the motor can be sold. Additional Hi-Pot tests at full voltage on the windings are not recommended thereafter.
However, since the Hi-Pot test certifies that the insulation is sufficient to withstand excess voltage during operation, there may be some situations where the failure of a machine in service can cause serious damage or downtime as compared to a failure during the testing procedure which can be a planned repair.
If a second Hi-Pot test is necessary at some other point in the motor’s lifespan, the following should be observed:
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Posted on: August 28, 2014
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Please note that a good polarization index does not ensure that a motor will pass a Hi-Pot test, and/or that motor will not be damaged during the testing process. Any motor that is subjected to a Hi-Pot test runs the risk of being damaged in the process.
Posted on: August 28, 2014
The test should only be completed by qualified personnel.
The precautions and procedure in NEMA MG-1 and MG-2 standards should be followed.
Winding should be cleaned and dried prior to Hi-Pot Test.
Winding should be in good condition, i.e. passed IR (Insulation Resistance) and PI (Polarization Index) Tests. This ensures that the windings are free of any moisture or contamination.
The second test voltage (after manufacturer’s original test) should not exceed 60-80% of original manufacturer’s test voltage. Each subsequent test should use 20% less voltage than the previous Hi-Pot test voltage.