I have a 75-year old 115/69 kv tran
I have a 75-year old 115/69 kv tran
(OP)
I have a 75-year old 115/69 kv transformer, which serves a load area in Northern California. My studies show that I can improve the voltage profile on the 69 kv network by changing the fixed no-load tap on the 115 kv side. This would be much cheaper than installing capacitors on the 69 kv system. However, I have received feedback from field staff that because of the transformer's age, an attempt to change the fixed tap may damage the transformer. Has anyone encountered a similar situation; is this a legitimate concern?
Michael Sidiropoulos






RE: I have a 75-year old 115/69 kv tran
If the oil DGA and screening are ok, you might shutdown for a full set of tests, then change taps and test again, comparing results.
RE: I have a 75-year old 115/69 kv tran
Er, I can understand why staff wants to take a wide path around gear that was built in the 1920s. What are oil tests showing? It may be remotely possible to lower the oil and physically remove and reconnect leads to bypass the tapchanger contacts, or eliminate it altogether. A concurrent internal visual inspection may be sobering.
Is the 69kV-side voltage profile stable? If even seasonal adjustments are needed, as described it’s hard to imagine that any tapchanger adjustment could be any less than disastrous in terms of service continuity.
Seems like the transformer has given phenomenal service, and it may be high time to get in a high-priority order for replacement. The phrase “borrowed time” may apply here.
The transformer MVA is not specified, but locating a trailer-mounted rental substation may be in order, even without the tap change. The voltages are common for that region. Maybe it could be discussed with some TANC or COTP members.
I mean no offense in these comments, but best of luck to you.
RE: I have a 75-year old 115/69 kv tran
RE: I have a 75-year old 115/69 kv tran
RE: I have a 75-year old 115/69 kv tran
Raghunath
RE: I have a 75-year old 115/69 kv tran
The transformer is 60 MVA, built by Westinghouse in 1925. It probably belongs to the Smithsonian rather than here !
In any event, we replace transformers because of load growth, not age. The cost of a new transformer of this rating is about $1.5 million and we don't spend that kind of money without a real need.
Thank you all for your comments, you've given me some ideas. First, I'll see if they can do those oil checks. I will also see if we can justify a new transformer based on load growth.
Michael Sidiropoulos
RE: I have a 75-year old 115/69 kv tran
RE: I have a 75-year old 115/69 kv tran
Minor aside: There are some established regional oil-test labs that can provide containers and coaching if oil sampling is a new issue. www.actiinc.com/sampling/freestuff.html www.oliveoilsource.com/olivenews4-11.htm www.nttworldwide.com/products.htm www.transformerservices.com/Lab/Gastest.html