Way to Save Energy Bill By Power Down STand-by Transformers

[chlee-penang]

Hi,

I have a question seeking member's advice pertaining to operational safety and energy saving.

We have 4 sub-station each equipped with 2 transformers (1 station 11KV/6.6KV 10 MVA, 3 other stations 11KV/.433KV 2MVA) on 2x100% stand-by configuration , secondary feeding to two bus sections with a bus-coupler. Currently both transformers are supplying concurrently to the load with Bus-coupler OFF in one Sub-station, others carrying total connected load by one of the two transformers only.

As an effort to reduce energy cost, I intend to switch out one transformer on each Sub-station to de-energized stand-by mode, when carrying out schedule 11KV stand-by generator load test each month, taking that opportunity to rotate the duty/stand-by transformers too, by doing so, the Free Load losses of transformer can be eliminated.

The question is whether safe to leave the transformer in de-energize state for 1 to 2 month, switch it ON and OFF alternate month?

 

[Bobster]

Have you got a line diagram you could post up or PM me of this set up?

If I were leaving a transformer only for a month, I would only disconnect the secondary side of it, however there is far to little information currently to go off.

 

[Engineer54]

Have you got a line diagram you could post up or PM me of this set up?

If I were leaving a transformer only for a month, I would only disconnect the secondary side of it, however there is far to little information currently to go off.

To be honest i was looking at this thread earlier on, and couldn't really make out the system from the OPs description, and what he was trying to do?? A single line drawing would at least give us a fighting chance to know what he has there. Also need to know if it's all manual or all auto controlled, or part auto part manual....

 

[chlee-penang]

Attached is the single line diagram for one of the sub-station. Assuming currently all V.C.B. are in "ON" position except Bus Coupler V.C.B. #5 is in :OFF" position, since the each transformer is sized to cater for total connected load, I intend to totally power down one transformer for alternate month ( all VCB in "ON" position, except VCB #1 & #3, or #2 & #4 depending on which transformer taken out of service), wondering any concern of leaving the transformer de-energized for one month. I believe there will be energy saving on iron loss, though copper loss will increase in the unit in duty

Noted that the transformer is of oil immersed type with Nitrogen blanketing, however, one of the transformer always lost its Nitrogen pressure and not able to to detect the source of minute leakage

 

[Knobhead]

Leaving transformers deenergised for long periods is never a good idea. There’s the added problem of the switchgear degrading.

 

[Engineer54]

So what about the other 11KV/400V Subs and the stand-by generators??

So are any of these main switchboards automated or are they all manual switching??

What sort of company are you working for by the way??

 

[Rockingit]

If the three of you most likely to answer this would care to pad out some of your replies with some more explanation (even if not required by the OP) this could be quite a decent learning opportunity for many others of us. Such a thing is becoming rare on here!!

I've no idea why you wouldn't want to turn a tx off - do they complain if they get cold?!

 

[Knobhead]

Leaving transformers deenergised for long periods is never a good idea. There’s the added problem of the switchgear degrading.

Having just noticed the comment about the nitrogen blanketing leaking, I certainly wouldn’t turn that transformer off for any length of time unless it is for a permanent repair to be carried out. Given the OP’s location humidity is liable to cause problems.

E54, what difference does it make if the switchgear is automated or manual operation? So long as the protection works it should make no odds.

 

[Engineer54]

E54, what difference does it make if the switchgear is automated or manual operation? So long as the protection works it should make no odds.

It makes a world of difference if the OP's talking about ''Stand-by'' facility. For the life of me i've never understood a stand-by provision that operates on a manual basis. But that aside if the OP has an automated Generator changeover to take up the load, i want to see how this facility has been incorporated into the system...

 

[Engineer54]

Noted that the transformer is of oil immersed type with Nitrogen blanketing, however, one of the transformer always lost its Nitrogen pressure and not able to to detect the source of minute leakage

9 times out of 10 the leak will be from the pressure relief valve at the top of the TX body!! Are there any other tank penetrations at the top of the tank such as pressure gauge, or some other unused optional features that's been blanked off with screwed plugs or caps??