Insulation Resistance Test 1

[Photocell]

In the upcoming shutdown, we want to do the IR test and measure the winding resistance of generator winding. The generator is rated 11kV , 20.38 MW , 1337A, 0.8 pf. We dont have enough time in the shutdown open up things completed.
1. What can be the best way to measure winding resistance and IR test without opening the Terminal box?
2. What important test we must carry out (This is 12000hrs maintenance of the generator)

Thanks for your time and support

 

[RRaghunath]

11kV Generator circuit breaker could be the convenient place for measuring winding resistance and IR without opening the terminal box.
If it is only IR, generator neutral disconnecting switch point also can be considered.

For generator, I don't think you need to do much during 12,000hrs maintenance. winding resistance as measured at gcb terminals includes the connections and cable from generator to gcb and should provide you information in case there is loose connection anywhere and you can pickup the thread for doing some more checks. Same is with IR.

Hope the above helps.

 

[candu6]

One thing to consider is, what do you want this resistance measurement for. Resistance measurements are often used for trending the state of the windings over the life of the generator. If you wish to use your data for this purpose then you have to pick the same measurement point each time.
The further you move away from the generator, then small changes in your machine may become hidden in the total resistance of the circuit.

 

[jimknight]

Has anyone experience of a permanently installed automatic insulation resstance tester? I know of a proprietary piece of equipment marketed by Megalert, but I don't know how good it is and whether it would be a useful on-line condition monitor for remote applications such as wind farm generators?

 

[buzzp]

jimknight,
It is better to start a new thread but the Megalert only tests the insulation when the unit is shut down, as I understand it. It is connected all the time but not continuously monitoring (impossible to do while energized).

 

[UKpete]

The other factor you must consider when taking IR readings is the winding temperature. Hot windings give lower IR. If possible, have a look at IEEE 43 (Recommended Practice for Testing Insulation Resistance of Rotating Machinery) - highly recommended.

You may also like to look at the US Bureau of Reclamation notes:

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