What should transformer Oil and Winding Temp Trip?
What should transformer Oil and Winding Temp Trip?
(OP)
I have generally followed the belief that the oil temp trip (OTT) and winding temp trip (WTT) trip only the LV breaker of the transformer. Should the LV breaker not open within a certain time, then a trip is sent to the HV breaker.
Reasoning has always been that OTT and WTT are not inidcative of trfr unit faults (for that there is Buchholz, diff, pressure relief valve, REF, etc.) but rather overloading (OL). The remedy is thus to shed the load if the trfr is overheating.
This also cures the hotspots as these are related to the current flowing in the windings. With current gone, it is safe to have HV breaker closed and leave trfr energised.
Interested to hear other views/practices.
Thanks.
Reasoning has always been that OTT and WTT are not inidcative of trfr unit faults (for that there is Buchholz, diff, pressure relief valve, REF, etc.) but rather overloading (OL). The remedy is thus to shed the load if the trfr is overheating.
This also cures the hotspots as these are related to the current flowing in the windings. With current gone, it is safe to have HV breaker closed and leave trfr energised.
Interested to hear other views/practices.
Thanks.






RE: What should transformer Oil and Winding Temp Trip?
RE: What should transformer Oil and Winding Temp Trip?
RE: What should transformer Oil and Winding Temp Trip?
Even if the trfr has a hot spot, the remedy is to reduce/remove the load. Should the hotspot degenerate further localised gassing will eventually collect in the Buchholz leading to a Buchholz Alarm which then should initiate further investigation.
Regards.
RE: What should transformer Oil and Winding Temp Trip?
I'm with you on that one (tripping the LV that is), as high OT or WT is usually an overload condition and tripping LV saves calling out a SAP in the middle of the night to reset a HV trip, but some installations don't have the luxury of an LV breaker on the secondary of the TX, so then it has to be a HV trip.
Depending on the criticality of the installation, some companies alarm only on high oil or winding temp and allow time for the operators to reduce load.
RE: What should transformer Oil and Winding Temp Trip?
RE: What should transformer Oil and Winding Temp Trip?
RE: What should transformer Oil and Winding Temp Trip?
Regards
Marmite
RE: What should transformer Oil and Winding Temp Trip?
RE: What should transformer Oil and Winding Temp Trip?
Same issue in case of some distribution transformer with DGPT/DGPT2 relay.
Overload situation must be solved on the low level, overload protection, thermal image protection, etc of the LV breaker.
RE: What should transformer Oil and Winding Temp Trip?
RE: What should transformer Oil and Winding Temp Trip?
Thanks for all the replies. They confirm that I've not strayed off the straight and narrow regarding OTT and WTT.
Regards.