11KV/433v 2000KVA Cast Resin

[yiefang]

Dear All,
FYI...We had a problem with 11KV/433v 2000KVA Cast Resin Transformer. The details of transformer are as follows:

1. Type: DYHK
2. Manufacturer: ABB
3. Rated Power : 2000 KVA
4. Rated Current: 105A-2666A
5. Insulation Class: HV/LV – F/F
6. Winding Material: HV/LV – Cu/Al
7. Insulation Level: L175 AC28/AC3
8. Duration of short circuit max – 2
9. Serial Number:- 142981130/3 IEC 726
10. Year of manufacture: 1998
11. Frequency: 50 Hz
12. Vector Group: Dyn 11
13. Type of cooling: AN
14. Protection Class: IP00
15. Total Weight: 4.86 ton
16. Max Syst. Volt KV:12/1.1
17. Impedance:5.9%
18. Class: E2/C2/F1

The problem that we faced is, we found out that the busbar insulation melted. Please refer to the attachment. So, we changed the insulation with the new Raychem.
when the transformer energized around 1700A found out that the temperature is slightly increase to 80°C - 89°C instead of normal operation is around 55°C - 59°C. The temperature level setting for Alarm: 140°C and Trip: 145°C. After that we decided to shut down the transformer and carried out the IR, PI and turn ratio test. The results are as follows:-


Secondary Winding Primary Winding
Phase IR PI Phase IR PI
R 702G? 1.41 R 3.03T? 3.28
Y 699G? 1.90 Y 3.65T? 3.02
B 706G? 1.50 B 3.45T? 3.21


The turn ratio test as per attachment :

http://files.engineering.com/getfil...c387-4388-be97-7d8bb0958ddb&file=P1292633.JPG

Based on the result, is the transformer in good condition? Kindly, please advise us on the above situation.

 

[Zogzog]

Excitation current on phase W is odd and requires further investigation. Your symptoms suggest a high resistance connection, I would do a winding resistance test and check all bolted connection with a microhmeter.

Your insulation looks good.