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??

 

[chlee-penang]

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.

 

[Knobhead]

We calculated the iron losses were costing us £40,000 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.

 

[Besoeker]

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.

 

[Bobster]

Just noticed this thread had updates, ^^^^^ Nail on the head though.

 

[Knobhead]

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?

 

[chlee-penang]

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.

 

[Knobhead]

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.

 

[Besoeker]

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

A distribution transformer.

 

[Knobhead]

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.

 

[chlee-penang]

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.

 

[Knobhead]

We did have OLTC’s on the intake transformers. The first thing to be done would be to switch them from “independent auto” to “leader and follower auto” to balance the voltage. I’ll have to do a drawing of the setup later today.

 

[shanky887614]

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.

in the hospitals they can have big ups units to keep things running till it goes online.

in one of the hospitals ive had a look at.


they have multiple supplies from the grid with castel keys to swap essential/non essential if need be with backup ups and generators to keep things going.


i had a look at some nice drawings showing where all the suplies for the hospital went from and to.

i learned a lot that day by chatting to the estates after one buggered up the fuse carrier in a full distboard lol

 

[Guest55]

Some interesting insights there from T & E54 in the difficulty in efficiently managing large scale site distrubution.

mostly above my station but i doff my cap anyways.

 

[Engineer54]

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.

.

Please tell me you are joking, ... you need to shut down the companies entire MV /LV distribution system to test run the generator??? I've never heard anything so bloody ridiculous in all my working life!! Who the hell designed such a head banging system as that??


And you're worried about saving a few $'s by shutting down a couple of Transformers. Your company needs to be spending money to sort out it's site wise MV/LV distribution system, before thinking about saving a few dollars and screwing the overall system up even further by the sound of it....

 

[gnuuser]

Please tell me you are joking, ... you need to shut down the companies entire MV /LV distribution system to test run the generator??? I've never heard anything so bloody ridiculous in all my working life!! Who the hell designed such a head banging system as that??


And you're worried about saving a few $'s by shutting down a couple of Transformers. Your company needs to be spending money to sort out it's site wise MV/LV distribution system, before thinking about saving a few dollars and screwing the overall system up even further by the sound of it....

besides the best way to save money in an industry is to keep the machinery in proper working order. this means a rigidly followed planned maintenance system. for example current draw monitoring & proper lubrication of equipment.
well lubed machinery creates less friction on motors, less workload equals less current draw
less current draw equals a lower power cost.
also on the note of preventative maint. dirty cooling fins on motors!
dust build-up on cooling fins can cause excessive heat retention in a motor, this can cause early failure of the lubricant and early failure of bearings. drastically reduced active life of the motor.
simply setting up a schedule of frequent cleaning (blowing dust out with compressed air) can keep a motor running for many many years.

 

[Knobhead]

Please tell me you are joking, ... you need to shut down the companies entire MV /LV distribution system to test run the generator??? I've never heard anything so bloody ridiculous in all my working life!! Who the hell designed such a head banging system as that??

We’re back to that again. There’s a big difference between a hospital and an industrial plant where the loss of power is no great shakes.

If the plant can cope with an outage why waste money on unnecessary expensive equipment? Admittedly it’s inconvenient but it’s not the end of the world.

How many places are there with no standby power at all? They manage.

 

[Engineer54]

We’re back to that again. There’s a big difference between a hospital and an industrial plant where the loss of power is no great shakes.

If the plant can cope with an outage why waste money on unnecessary expensive equipment? Admittedly it’s inconvenient but it’s not the end of the world.

How many places are there with no standby power at all? They manage.

Are you actually telling me this is common practice, Come on Tony pull the other leg it's got bells on!!! I haven't only worked on Hospital Stand By systems, be they MV or LV.

Black out an entire company's site to load test a generator, ....the design is a complete NONSENSE, this has nothing to do with the system being automated. We both know there is absolutely no reason to shut down a complete site to bring a generator online, especially just to load test the bloody thing!!

 

[Knobhead]

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.

We did have OLTC’s on the intake transformers. The first thing to be done would be to switch them from “independent auto” to “leader and follower auto” to balance the voltage. I’ll have to do a drawing of the setup later today.

Red is the supply company’s equipment
Blue is our equipment

You can see what the results would be if a bus coupler anywhere in our system was closed without either the 33 or 132KV bus closed.
It only took a phone call as the supply company’s switchgear was remotely operated but they charged us for every time they pressed a button.

 

[Knobhead]

Are you actually telling me this is common practice, Come on Tony pull the other leg it's got bells on!!! I haven't only worked on Hospital Stand By systems, be they MV or LV.

Black out an entire company's site to load test a generator, ....the design is a complete NONSENSE, this has nothing to do with the system being automated. We both know there is absolutely no reason to shut down a complete site to bring a generator online, especially just to load test the bloody thing!!

We don’t know how the generator is tied in to the OP’s system.

I’ve wrongly referred to standby, it should be emergency.

I didn’t say its common practice in the UK, that’s your inference.
If it won’t cause problems and the company can put up with the inconvenience who are we to criticise?
From the contacts I have in Malaysia a power outage isn’t unusual. It isn’t unusual for a plant to have a backup system. What is unusual is for them to actually test it.
Many are running purely on generators with no backup.

Our emergency generators were remote from the intake. In the event of a major failure power is transmitted via the MV network to wherever needed, everything else would be isolated. We could generate only a tiny portion of the intake total to keep essential site services going.
The only time I’ve known an emergency system used in anger. The RAF had to fly food in as the works was totally snowed in and all the power lines were down.

Yes I have worked on fully automated systems with UPS backup. But in general industry they are few and far between.

Our two data centres each had their own standby system. The joys of multinationals, they’ll spend money like water for the management side of things. You try getting money out of them for essentials.

 

[Engineer54]

We don’t know how the generator is tied in to the OP’s system.

I’ve wrongly referred to standby, it should be emergency.

I didn’t say its common practice in the UK, that’s your inference.
If it won’t cause problems and the company can put up with the inconvenience who are we to criticise?
From the contacts I have in Malaysia a power outage isn’t unusual. It isn’t unusual for a plant to have a backup system. What is unusual is for them to actually test it.
Many are running purely on generators with no backup.

Our emergency generators were remote from the intake. In the event of a major failure power is transmitted via the MV network to wherever needed, everything else would be isolated. We could generate only a tiny portion of the intake total to keep essential site services going.
The only time I’ve known an emergency system used in anger. The RAF had to fly food in as the works was totally snowed in and all the power lines were down.

Yes I have worked on fully automated systems with UPS backup. But in general industry they are few and far between.

Our two data centres each had their own standby system. The joys of multinationals, they’ll spend money like water for the management side of things. You try getting money out of them for essentials.

I've asked the OP how the generator(s) are hooked up in his system and had nothing back. I have no idea at the moment if the generator(s) in question are MV or LV, i'm assuming at the moment they are MV...

The only area one would then be interested in, is then the MV bus, and if as shown in the single line drawing there are bus couplers, a generator or generators could quite easily be incorporated on that bus. We are basically talking blind here, as the OP states they have 4 subs on the site one 11kv /6kv and 3 X 11kv 0.433kv. We don't know if the 11kv is distributed on an open ring, distributed from a main or central Sub via radials, or individually supplied by the local electricity company. We also don't know if the standby generator(s) covers the whole distribution system or section(s). Either way it's not physically a problem to incorporate stand-by facilities WITHOUT having to shut down the entire sites distribution system....


Perhaps it is just me, but i can't see how any company Factory(s) that requires the amount of energy as indicated by the OP can substantiate a total blackout to test run a generator or generators. It's a totally alien philosophy, that i've never come across or even heard of during my working career.


Oh and BTW i have worked in Penang, well just across from Penang at the Butterworth military air base back in the 80's, when the Aussie's air force were based there. Refurb of aircraft hangers and associated workshops, that involved a pretty extensive MV ring too with stand-by facilities. But the base wasn't shut down to bring the those stand-by facilities on line!! lol!!