Tripping of Transformer on Rapid Pressure Rise Relay 1

[kashali]

We have 08 ABB hermetically sealed transformers installed in 1996. Transformers T1 & T2 are of 8000 KVA and the remaining T3 to T8 transformers are of 1200 KVA rating. 

These transformers remain in continuous service since installation and we regularly perform inspection & testing of these transformers in our annual shutdown.

On September 03, 2014 (10:30 am), Transformer T1 tripped on Rapid Pressure Rise Relay (RPRR). 

Following are the observations taken just after tripping:
- RED indication on Seal in Relay of RPRR.
- Load Current at the time of tripping was 550 A (approximately).
- No abnormal current logged by Current Protection Relay PS-451.
- Following gauge readings were taken just after tripping of Transformer:
- Ambient Temp : 38 degree C
- Vacuum Gauge Reading : 0 PSIG (Not always zero, changes with temperature and load)
- Oil Level Reading : OK
- Temp Gauge Reading : 45 degree C

Following Tests were conducted on T2 after tripping:

- Insulation Resistance Test - OK
- TTR _ OK
- DC Winding Resistance Test - OK
- DGA/ Oil Test conducted in February, 2014 and in September, 2014 (after tripping).
No change in DGA results.

We do not find any cause of tripping. Transformer is energized at no load on September 09, 2014 and no further tripping observed.

Please, advice any suspected cause of tripping of transformer on Rapid Pressure Rise Relay.

 

[kashali]

Reply to PRC:
Yes, RPRR and Sudden pressure rise relay are same. Sorry, I mean RPRR & Pressure relief device(PRD).

In my experience, we have 25 Conservator type transformers with Buchholz's Relay and 08 Hermetically sealed transformers with RPRR. These, transformers are in continuous service since last 17 years.

During this long tenure, we have not experienced any false tripping of Buchholz's Relay. But RPRR tripped twice and we did not find any cause of tripping.

 

[prc]

Thank you kashali.My experience is also same as yours. Bucholz relays rarely maloperate,but SPRR are always prone to maloperation with external faults or tank vibrations etc.