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The Importance of a Sacrificial Stator Coil in Factory Acceptance Testing


Sacrificail Stator CoilFactory Acceptance Testing (FAT) is becoming more common in large motors purchases and repair validation. Many end users are starting to establish specifications that include every test imaginable to ensure that the motor is designed and built to the specification provided and will last as long as current technology and testing procedures allow.

One test that should not be neglected is the sacrificial stator coil test. In this test either two or three extra stator coils are made with the set. These coils are then put through the same preheat, VPI cycle, and bake process as the complete stator.

After the VPI process and before baking, one of the sacrificial coils can be cut open to ensure complete penetration of the resin. If coil insulation is not completely penetrated with resin, the stator can be put back into the VPI tank.

The second coil is inspected after the bake cycle. This coil is cut in half and a visual inspection is done to verify penetration and look for voids in the resin or coil insulation.

The third coil can then be put through destructive testing. A simulated stator slot is made by putting the coil between two pieces of metal.

A HiPoT test is done with a lead on the coil and a lead on the simulated stator slot. Voltage is applied until the coil insulation fails and arcs to the simulated stator slot. The voltage at the time of the insulation failure is recorded.

With all of the FAT tests that are available, the sacrificial coil should be considered. API standards 546 and 541 are a good resource for additional acceptance criteria.

The video below is part of a sacrificial coil test on a 11,500hp motor. The intent of the test is to take one of the extra stator coils that has gone through the same insulation process as the stator and apply voltage until it fails. This was a 13,200 volt motor and the coil failed at 74,000 volts. 


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Bob Bolhuis

HECO - All Systems Go



About the author:

Bob Bolhuis  is the Business Development Manager, Large Machines & Projects for HECO - All Systems Go. Bob has over 30 years of experience in the electric motor industry with a focus on large electric motors. Bob has been instrumental in the implementation of a variety of Motor and Powertrain Performance Systems that HECO has partnered with end-users on. 

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