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Topic Title: Insulation resistance
Topic Summary: Transformer insulation resistance procedure and method of connecting test leads
Created On: 24 October 2013 05:19 AM
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 24 October 2013 05:19 AM
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vvvviswavijay

Posts: 39
Joined: 11 September 2003

Hi Professionals,



I need to clarify the testing procedures for performing insulation resistance method adopted for HV transformers above 50 MVA to 100 MVA as per IEC 60076-part 1 & Part 3/ BS standards. Transformers have Dyn11 conenction with 3 Phase 33kV HV side and 3 phases on 690 V (LV) on secondary side.

My method is to use megger.

1. Ensure the transformer incoming is isolated using proper PPE's.
Adopted proper LOTO & PTW.

2. Check for absence of voltage before measuring and address the boundary of working.

3. Note down the oil, winding and ambient temperature.

4. Disconnect all the LA's, HV, LV cables and neutral earth.

5. For HV side measurement,

a. Connect 1U - E to respective megger terminals. crank 5kV for
1minute using megger. Note down the value in MOhms. Similarly
repeat for 1V-E,1W-E.

b. Similarly perform the same measurement between the phases. Say
1U-1V, 1V-1W, 1U-1W and note down the readings.

6. For LV side measurement,

a. Connect 2U - E to respective megger terminals. crank 2.5/ 5kV
for 1 minute using megger. Note down the value in MOhms.Similarly
repeat for 2V-E,2W-E.

b. Similarly perform the same measurement between the phases. Say
2U-2V, 2V-2W, 2U-2W and note down the readings.

7. For HV-LV side measurement,

a. Shorted all the 3 phases on HV side with a jumper cable. Similarly i
shorted the 3 phases on secondary side. I connect the leads from
HV and LV to megegr terminals. Crank 5kV for 1 minute and note
down the readings.

Request to confirm whether my above procedure is correct or wrong?

I need the guide line values or IR for good transformer while installed and during service in 6 months and 1 year?

Thank you for your time and awaitign for your suggestions.

Best Regards
Vj
IET » Energy » Insulation resistance

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