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

[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.