Electromagnetic Imperfection Testing

The stator core in rotating electrical machines is made of thin stacked laminated steel segments, which are insulated from each other by a layer of varnish to minimize losses. If lamination shorts occur, a loop current causes local hots spots, which, in the worst case, can lead to a partial meltdown and expensive damage in the machine. 

Verify the integrity of stator core insulation

The electromagnetic imperfection test (also known as stray flux measurement, ELCID) is performed to detect stator core interlamination imperfections that can eventually cause overheating and damage to the stator core of motors and generators when in operation.

Stator core measurements should be performed on a regular basis to evaluate the insulation integrity between the stator core layers of a machine during factory acceptance testing and commissioning, as well as after the machine has been put into service. The test results are compared with previous test results to verify stator condition.

Reliable fault detection 

Since faults cause imperfections in the magnetic circuit of the stator core, they can be easily detected by an increase of the stray flux in amplitude and/or a change in the phase. Additionally, failures can be detected by comparing the measurement results of different stator core areas with each other.

The test is performed offline during bigger maintenance shutdowns. The rotor is pulled out for the test to get access to the stator. With our complete stator core measurement solution, the stator core is energized with a small percentage of nominal flux and the stray flux on the surface is measured along the slots. 

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