Generator / Motor winding Tan-Delta (PF) test

[mohanlal]

The generator / motor winding power factor or tan delta test was carried out for the 3.3 KV equipments. The generator ratings are 8.0 MW & motor ratings are from 175 KW to 1600 KW.
The test referred to as Tip-up test is performed at a number of levels of voltage from 25% to 100% of line to ground voltage to obtain the PF vs voltage chs. PF Tip up value is defined as the difference between the PF
measured at the line to ground voltage and the PF measurred at teh lowest voltage in the test range (usually 25% of the line to ground voltage.)
The double system includes online DTA expert condition evaluation software,which evaluates and rates the dielectric condition of the insulation tested
from the test results by comparison against the limits of PF of reliable winding insulation of units of identical make, type, and ratings with the unit tetsed as well as against previous test records of the unit where
available.
In such test one of the generator is having % PF of average 6% for phase to ground and 3 % for phase to phase. If the insulation is epoxy-mica, then the % pf is high and indicates possible deterioration.
Recommended to test it again within next three months to monitor the trending. Now the equipment is on line.
Could anybody conclude from the test values and what is required to be done next?
I request Ragunath also to join in this question forum.
Thanks,
Subramanian

 

[motorspert]

At 3300V we would not recommend Tan delta testing. the coils won't have corona sheields, so the earting is dodgy and readings would be unreliable. Also, at such low phase voltages there would not be any discharges within the coils. We only test at 4500V and above even at 4500V teh value of the test is debatable.

By all means repeat in three months - but ask the company or persons who are doing the tests for you to justify why you need them.

 

[edison123]

I agree with motorpsert. IEEE 286 states that PF and tan delta is useful for 6 KV and above. 3.3 KV motors do not have stress grading and anti corona systems since the partial discharges start at over 6 KV.

* Homer Wisdom - "Operator, Give me the number for 911" *

 

[vmere]

TAN/DELTA testing of transformers & motors.

We have 30mva transformers with open air 132kv hv bushing.

i require information/explanation on how to do this test & why is required. What are expected values from tests. Does this give one a foot print of the insulation of bushing/winding, etc?