Power transformer in storage

[ters]

A 30 MVA oil filled transformer (115 kV) will be put onto the temporary pad with oil contentment for about 2 years, de-energized, in Canada. What considerations (re moisture, etc) should be given? Thank you.

 

[itsmoked]

If it is open to the atmosphere you need to keep it 2-4degrees above ambient at all times. Bar heater? Has it got forced oil circulation? Wire that permanently on. Clamp a bar heater to the external loop perhaps?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[oldfieldguy]

If it has an inert gas pad, that must be maintained. Think of hooking up power to the cabinet heaters to keep condensation out of auxiliary cabinets. Dessicant packs are a less desirable alternative.

An annual test of an oil sample isn't expensive. It shouldn't show any changes to a stored transformer, but who knows?

Any mechanical components such as load tapchanger mechanisms should be evaluated. A preservative coating might be needed.

It's a good idea to do a monthly visual check of the thing, just to make sure somebody hasn't backed a truck into it, or some other such catastrophe...

old field guy

 

[dpc]

If it has inert gas system, this must be kept in service and the nitrogen bottles must be monitored and replaced as needed. For a conservator-type transformer, the dessicant in the breather should be replaced as needed.

As mentioned, if there are strip heaters in the control cabinets, these should be connected to power.

To be honest, the best thing would to energize it, but the key thing is to keep moisture out.

 

[ters]

Thank you very much itsmoked, oldfieldguy and dpc. I'm not sure what exactly the transformer desing is (inert gas system or not), still awaiting info. As per SLD, it seems to have forced oil circulation, so that sounds as a practical idea to wire it permanently on and use some external heaters.

We had another case where we permanently energized a large spare transformer, and let it idle indefinitely (the Client did not mind paying for losses). This time we cannot consider that option (it is in a storage area) but I was even thinking of suggesting a crazy solution of permanently energizing it from the low voltage side (34.5 kV) with something like 3x208V and short the HV side...

 

[itsmoked]

While temping the creation of that serious HV would not be worth the risks.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[davidbeach]

What serious HV? 208 into the 34.5kV side would produce less than 700V open circuit on the 115kV side. But since he would short circuit the HV side, the voltage would be zero. Really not a bad way of putting some current into the transformer. Select your x-208V transformer such that its impedance plus the impedance of the 30MVA transformer keeps the current level in the x-208V transformer within its ratings and you should be fine. If you've got good data on the big transformer, you would want to size your system to supply the no load losses it would have at 208V plus the "full load" losses associated with your shorted high side. There shouldn't be any worries about too much current in the big transformer.