transformer insulation tests

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panthripu

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Hi everyone
Just want to know about the insulation test in transformer. We conduct IR test in our oil filled transformers on regular basis. We did polorization index test and tan delta test also a couple of times. Now I want to know , if it is really logicall to make all three tests as all tell us about the level of winding insulation . Is one of them is not sufficient ?
Just for information , we also send the oil for DGA test periodically.
 
Just to clarify when you say "IR" test do you mean "insulation resistance" or "Infrared"? Reason I ask is that you make the statement "all three tests". Assuming in the context here that you are meaning Insulation Resistance test then the PI (Polarization Index) test is in fact an insulation resistance test, just timed for 10 min duration. A tan-delta or power factor (such as Doble) is the superior test for insulation. We do the PI, Doble, TTR, and the oil tests (liquid and DGA).

A complete list of testing and interval recommendations are available in NETA MTS or NFPA 70B.
 
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BPoindexter said:
Just to clarify when you say "IR" test do you mean "insulation resistance" or "Infrared"? Reason I ask is that you make the statement "all three tests". Assuming in the context here that you are meaning Insulation Resistance test then the PI (Polarization Index) test is in fact an insulation resistance test, just timed for 10 min duration. A tan-delta or power factor (such as Doble) is the superior test for insulation. We do the PI, Doble, TTR, and the oil tests (liquid and DGA).

A complete list of testing and interval recommendations are available in NETA MTS or NFPA 70B.
Click to expand...
Although all tests can indicate insulation failures, are some of them more suited than others to indicate insulation degradation short of actual failure or to predict impending failure?
 
GoldDigger said:
Although all tests can indicate insulation failures, are some of them more suited than others to indicate insulation degradation short of actual failure or to predict impending failure?
Click to expand...

My concern has always been on tests that stesses the insulation and what affect it has on the insulation life itself.
 
Thanks for your comments..but i need some more comments as i believe that still the comments above are not helpful.
 
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