Need practicle experience regarding the subject. 1

[mns15451]

What is the crieteria of performing the DC Leakage Test on the stator or rotor of 13.8 Kv, 100 Mva generator that has run over 100,000 hrs? Why it is considered harmful for the winding insulation? If we don't perform this test or Hipot test then how we can evaluate the condition of insulation of generator winding.

 

[electricpete]

What is the crieteria of performing the DC Leakage Test on the stator or rotor of 13.8 Kv, 100 Mva generator that has run over 100,000 hrs?

IEEE will give you guidance about the test voltage and test method.
Specifically for service-aged transformer, 125 – 150% of 1.7*VLL, which gives max voltage of 28-33kvdc. Only to be performed after successful IR/PI and only by knowledgable personnel.

Why it is considered harmful for the winding insulation?

I would call it “potentially destructive” in the sense that your machine may be unuseable during the test. However if properly applied, that should not occur for a good machine, only for a machine that was marginal anyway… and if it was a critical machine where downtime is intolerable, AND you have a spare available so that failure during test is acceptable, then you may prefer to fail it now during test rather than take a chance on failing in service a few years from now. On the other hand for non-critical machine, you might not want to do that.

If we don't perform this test or Hipot test then how we can evaluate the condition of insulation of generator winding

Visual inspection during outage. Power factor / tan delta. Partial discharge (on-line or off-line). Surge test.


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[electricpete]

Correction
”I would call it "potentially destructive" in the sense that your machine may be unuseable during the test. “
Should have been
”I would call it "potentially destructive" in the sense that your machine may become unuseable as a result of the test. “


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[electricpete]

By the way IEEE 95 is the reference I meant to mention. Here is more info:

http://www.usbr.gov/power/data/fist/fist3_1/vol3-1.pdf

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[ScottyUK]

If it is an air-cooled machine then an offline PD test will give you a lot of information about the state of the insulation. An RSO test will also provide a lot of useful information. Both tests require an experienced tester to fully interpret the results.


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