Discuss Way to Save Energy Bill By Power Down STand-by Transformers in the Electrical Forum area at ElectriciansForums.net

Welcome to ElectriciansForums.net - The American Electrical Advice Forum
Head straight to the main forums to chat by click here:   American Electrical Advice Forum

C

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?
 
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.
 
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....
 
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

Way to Save Energy Bill By Power Down STand-by Transformers untitled.JPG - EletriciansForums.net
 
Leaving transformers deenergised for long periods is never a good idea. There’s the added problem of the switchgear degrading.
 
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??
 
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?!
 
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.
 
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...
 
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??
 
E54 : Yes, there are pressure gauge and relief valve mounted on the TX, we have checked and tightened all items that may leak. Probably we did not have the right method for checking minute leakage. The 11KV/.433KV station has similar configuration.

Tony: Thanks for your valuable advice. What about those TX without Nitrogen leakage? According to technical data of TX, there are few KW losses, if the idle TX can be switched off for a month or two without potential problem, surely can save some $/month.
 
Last edited by a moderator:
We calculated the iron losses were costing us ÂŁ40,000 per year for our intake sub 4x20MVA 33/11KV. We considered shutting 2 of them off at the weekend and plant shutdowns when demand was low.
It was decided the problems of regular switching outweighed the saving. Our 33KV OCB’s were under the control of the midlands grid control room, we could turn them off, grid control had to turn them back on.
For us to close the 11KV bus to parallel the transformers during the change over had a knock on effect on the local grid 33KV and 132KV bus.

We gave the idea up as a bad job.
 
I slightly different take - apologies if it has been already covered.
If the objective is to save energy (per the OP) and attendant costs, de-energising a transformer is hardly likely make a significant difference.
In my experience, and I have to give guaranteed efficiency figures, on load losses don't often exceed 2% for the sort of transformer on the single line diagram. And off load, significantly under under 1%.

There are much more effective ways of reducing energy consumption.
 
on load losses don't often exceed 2% for the sort of transformer on the single line diagram. And off load, significantly under under 1%.

I must be missing something here. What type of transformer is shown in the drawing?
 
Thanks Tony.

In our case we probably have an advantage, as we require to test run the 11KV stand-by generator with load in every one or two months interval, as the switching is designed for manual operation mode (no issue for the plant to have short duration black out), and each time changing over from Public Utility to generator, we need to switch off the transformer anyway. As long we do not have to carry out any test to turn on the transformer that been de-energized for 1-2 months, it is worthwhile to reduce the iron loss.
 
Until you get the nitrogen leak fixed I wouldn’t turn that transformer off. E54’s comment about the pressure relief is worth following up, they’ve caused me problems in the past. Low pressure would shut down the transformer.

The other transformers I assume have conservators with a breather. The breather needs a silica-gel unit that must be properly maintained as I expect you have quite high humidity given your location. Too often they get ignored and cause problems later with the transformer oil.

You really need to talk to the transformer manufacturers regarding the losses of each unit and work out the savings and the risks to your plant.
 
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...

The plants I’ve worked on that had standby generators the switching was all manual. I can understand it for a hospital but the expense couldn’t be warranted for us.
 
Thanks Tony. In our case is a bit different, there is electrical and mechanical interlock to prevent paralleling the transformers as well as paralleling utility power with stand-by generator.

Each time test run of generator with load, we need to power down the entire distribution network within our plant (total blackout), as such there is no issue of switching.

It is interesting to note that you have a knock on effect when paralleling 11KV transformers, isn't there an instrument to check and enure in phase as well as minor voltage different before paralleling the transformers? I guess the 33KV/11KV transformer is equipped with OLTC that has an AVR to regular the secondary voltage.
 

Reply to Way to Save Energy Bill By Power Down STand-by Transformers in the Electrical Forum area at ElectriciansForums.net

OFFICIAL SPONSORS

Electrical Goods - Electrical Tools - Brand Names Electrician Courses Green Electrical Goods PCB Way Electrical Goods - Electrical Tools - Brand Names Pushfit Wire Connectors Electric Underfloor Heating Electrician Courses
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc

Electrical Forum

Welcome to the Electrical Forum at ElectriciansForums.net. The friendliest electrical forum online. General electrical questions and answers can be found in the electrical forum.
This website was designed, optimised and is hosted by Untold Media. Operating under the name Untold Media since 2001.
Back
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock