Power Transformer Storage

[johnnyball]

What are some criteria to consider in letting a three-phase 18/24/30 MVA 154/13 kV power transformer sit idle for long periods of time. My particular unit has a nitrogen pressure system and heaters installed on the unit. Is there any detriment in letting the unit sit idle?

 

[edison123]

I think that with the pressurized nitrogen system and heaters, you have got things covered.

Muthu

http://www.edison.co.in

 

[dpc]

I agree with Muthu. It's probably always better to keep it energized, but as long as you keep the nitrogen on it and have a functional low-pressure alarm system that someone is actually monitoring, I would not be overly concerned.





"Theory is when you know all and nothing works. Practice is when all works and nobody knows why. In this case we have put together theory and practice: nothing works... and nobody knows why! (Albert Einstein)

 

[waross]

That sounds like a good system.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[cranky108]

You might want to monitor some of the alarms. Mostly oil levels.

 

[Zogzog]

I also agree with the other guys, but be sure to do full run on tests before bringing back on line

 

[prc]

How long to store.In case you plan more than 6 months,better to store under oil filling.Most manufacturers will demand for that.But keep with conservator plus breather.In case you are keeping a gas cushion over the oil level,check with manufaturer to find correct oil level,so that excess pressure or vaccum is not generated in the gas cushion.But never store with complete oil filling without space for oil expansion due to ambient air temperature.I came across a case where oil was filled fully in the transformer and stored. The tank welding ruptured and oil started leaking.

 

[TurbineGen]

@dpc - I have heard that a transformer in storage should be energized, but I don't know why. What is the rationale behind that? Should you energize it with reduced voltage or full voltage?

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If it is broken, fix it. If it isn't broken, I'll soon fix that.

 

[dpc]

If it is truly in storage, it's probably not practical to energize. But keeping it energized keeps the core and oil warm and helps keep water away from the windings. In theory, with good oil, a well-sealed transformer, and an inert gas blanket on top of the oil, there should be no water inside and no way for it to get in.

"Theory is when you know all and nothing works. Practice is when all works and nobody knows why. In this case we have put together theory and practice: nothing works... and nobody knows why! (Albert Einstein)

 

[VTer]

Is it not true that if the nitrogen blanket pressure falls certain psi # below the outside atmosphere, the bleeder valve allows outside air into the tank which pulls in moisture and oxygen. I would assume that for that reason you want to monitor your gas pressure and keep the oil from contracting with low temperatures.

"Throughout space there is energy. Is this energy static or kinetic! If static our hopes are in vain; if kinetic — and this we know it is, for certain — then it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature". – Nikola Tesla

 

[VTer]

or keep adding gas to keep the pressure up when it does

"Throughout space there is energy. Is this energy static or kinetic! If static our hopes are in vain; if kinetic — and this we know it is, for certain — then it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature". – Nikola Tesla

 

[tlrols]

In a perfect world you would recirculate the oil within the transformer while it is in storage. This is seldom done however...what you describe strikes me as better treatment than most transformers receive when they are placed in storage.

 

[johnnyball]

Thanks everyone for their valuable info. I hope everyone has a great new year.

 

[haisa]

Is it Possible to apply a low voltage of say 415V and then short the Secondary, so that the little current flowing keeps it warm?

 

[TurbineGen]

That depends on the unit. If you short the secondary, you might be drawing more than your rated current. It depends on your impedance and the voltage rating of the transformer. If the transformer is in the transmission voltage class (69 kv and up) this might be fine.

You need to multiply your % impedance by the voltage rating of the transformer which will give you the maximum voltage you can use on the primary and short the secondary. I would then choose a voltage around 10-20% of that.

For example: Say you have a 34kV transforer with 10% impedance. The highest voltage you could put on the primary with the secondary shorted would be 3400 volts. However, this will draw full load current on the secondary! Not a good idea. Thus you take about 10-20% of that value for storage. So 340-600 volts or so would be ok to keep it warm.

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If it is broken, fix it. If it isn't broken, I'll soon fix that.

 

[edison123]

haifa
OP mentioned heaters to keep the windings warm. Then why all the hassle of the disconnecting the HV line, applying the 415 V and shorting the LV, monitoring the current, protecting the sc arrangement etc. and then undo everything when the trafo is needed for quick service ?

Muthu

http://www.edison.co.in