Sudden Pressure and Low oil Level TRIPS for < 5MVA Dist. Transformers

[Uquresh1]

I have a customer that has recently installed a 4.75 MVA distribution transformer (23/4.2kV)that comes on a skid that also has a recloser, regulators, and isolation/bypass switches. I have fuses protecting the transformer on the high-side. The only trips on the transformer were for 63FPX (Sudden pressure), 71Q (Low oil Level), and 81F (U.Freq). Now the customer just received the transformer and the 63FPX and 71Q devices on it don't have TRIP level contacts, only Alarm level (and there's one of each, no extras to program for Tripping).

So question is: For a small transformer like this, is it OK to not have 63FP and 71Q protection? Should I OK the design, or ask them to have the 63FP and 71Q relays installed before puttng this TXfmr in service?

I don't have a lot of experience with small Txfmrs like this, so any help would be appreciated.

Thanks.

 

[stevenal]

What would you trip, the low side recloser? This would leave the transformer energized from the high side until the fuses cleared anyway.

 

[Uquresh1]

Exactly. The only device I can trip is the recloser. So I can only isolate for conditions caused by through faults. But is this reason, that there is nothing on high side to trip, enough to say that I don't need to have 63/71 trips?

 

[dpc]

I'd say so. Sudden pressure detects internal faults - if it trips for through faults, that is a misoperation. And low oil level is an internal transformer problem.

As for the question "Is it OK?" - it depends. There are thousands of transformers larger than this one that have only primary fuses for protection. This is because of cost. Is it worth spending an extra $100K to reduce potential transformer damage? That depends on how costly an extended outage would be, alternate power sources, available replacement transformers, and the cheapskate index of the owner.

 

[prc]

The tripping should be of primary breaker. Believe it is a sealed unit with out conservtaor and gas opertaed relay. If so, best way is to use the alarm contcats of sudden pressure relay and low oil level as trip contacts.Alarm contacts for these functions are unnecessary.