I've seen this application SUGGESTED in a few relay manuals. Sudden pressure trip coming in via relay BIs and then blocking this trip using through fault detection within the relay. I've never actually seen this applied and I wouldn't recommend it. Will the transformer be experiencing a high rate of through fault currents?
On the other hand, a through fault could cause transformer failure which would call the logic into question. Sounds like a solution to which there is no known problem.
Regards
Marmite
Thanks for the article. I need to change our philosophy to use the current supervison logic suggested in the article.
A false trip of a sudden pressure relay on a through fault could keep a generator off line for a couple days while transformer tests were conducted. I guess we were lucky to not have a false trip.
Some transformers are subject to sudden pressure relay operation due to mechanical forces on the transformer during system faults when no electrical fault is present inside the transformer tank. This can be due to winding shift and subsequent oil movement, or it can be due the location of the sudden pressure relay on the tank wall. One method to mitigate exposure to tripping undesirably for high-current external through-faults is to supervise the sudden pressure relays with an instantaneous overcurrent relay that will block tripping for currents that exceed a relatively high threshold.
How is the practice in Europe and US? I thought you are using SPR only in transformers with nitrogen sealing.Or are you using it in transformers with conservators also as a back up to Buchholz relay.I always suggest to avoid SPR in transformers with Buchholz relay.
When through fault currents pass through transformer, windings start oscillating vertically due to dynamic axial compressive forces( copper and press board act as masses connected by springs).This in turn create pressure waves in oil.
Rcwilson,I think you need not worry much in generator transformers as magnitude of through fault current in such transformers will be very much less compared to network transformers.Normally generator impedance will be almost double of transformer impedance and this total impedance will limit fault current 3-4 times full load current and hence winding oscillations will be less.
prc,
here in Italy we use SPRs on EHV/HV interconnection autotransformers, without block. SPR and Buchholz realay settings must comply with transformer design in order to not misoperate in case of external faults or seismic events. Thus even if SPR is not inhibited during faults false tripping is actually not an issue.
