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kasrop
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Join Date: Nov 2016
Posts: 38

Stator Test Results

06/12/2019 2:25 PM

Dear all

we test main stator for old generator 35MVA,5KV manufactured in 1973 by megger

5kv the insulation resistance result is 37MΩ.are this result acceptable or not

because its old generator and we dont have the test report to compare the result.

Thanks for all
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SolarEagle
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#1

Re: stator test

06/12/2019 2:57 PM

https://www.instrumart.com/assets/Megger-Guide-to-Insulation-Testing.pdf

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HiTekRedNek
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#5
In reply to #1

Re: stator test

06/13/2019 5:35 AM

Sorry,SE

When I first read the OP,there were no replies,so I googled for info.While I was googleing,you were posting.I did not reload the page before I loaded my reply .If I had I would have seen your reply,and I would not have duplicated the effort.

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HiTekRedNek
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#2

Re: Stator Test Results

06/12/2019 3:07 PM

Here is a link to information that will probably answer all of your questions.

At first glance, according to the limited information you provided,the generator is ok,but there are other factors to consider before giving it the green light.

Read the information on the link and you will gain an in depth knowledge of the process.

Good luck!

https://www.instrumart.com/assets/Megger-insulationtester.pdfhttps://www.instrumart.com/assets/Megger-insulationtester.pdf

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Stef
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#3

Re: Stator Test Results

06/13/2019 2:07 AM

If I came across readings as low as 37M Ohm for a 5KV generator of that era 1973 I would recommend a drying out in an oven or with space heaters as the slot insulation may have absorbed moisture. From testing similar equipment the resistance at 5KV should be at least 200+M ohms though for 3.3KV up we used a 10KV Trimax brand insulation tester and recorded the resistance at 1 minute and 5 minutes intervals.

Do you know what form of insulation is used on the windings, paper, enamelled, varnished cloth?

When heating the stator, we took the temp to 70 deg C, measure the insulation hourly and you will find that if it is moisture the resistance firstly high will fall as the moisture migrates through the windings and then rise again as the windings dry out. After drying the stator should be varnished but that may be impractical.

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Power Prof
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#4

Re: Stator Test Results

06/13/2019 5:24 AM

To really know if a stator is OK, the megger is only the start. If you get a good polarization number, then your stator is good enough to do all of the rest of your testing. If all of those tests are OK, the over-potential (Hi Pot) test gives you relatively high confidence that the stator will not fail, soon, in service.
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PWSlack
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#6

Re: Stator Test Results

06/13/2019 1:21 PM

If it is not known beforehand where the OK/Not-OK boundary lies, then why bother carrying out a test at all?

Without a test protocol, all that has been obtained, is a measurement.

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