Thread: Leaking electricity from transformers.

Originally Posted by DaveKamp

I second JST's suggestion. Get a SMALL 480:240/120 transformer to leave on all the time, use it for your basic 120 loads AND...

A detection/control circuit for your big transformers. When your biz is shut down, drop out the contactors to the big transformers.

Are you suggesting having a larger transformer in parallel for large loads that is disconnected when not needed?

Paralleling transformers is doable but can behave unexpectedly when mixing different ones together.

Originally Posted by Strostkovy

Are you suggesting having a larger transformer in parallel for large loads that is disconnected when not needed?

Paralleling transformers is doable but can behave unexpectedly when mixing different ones together.

It is ok if they have exactly the same ratio.

Anyhow in washington state, far as i can tell, the additional kva charge by avista energy is 50 cents per kva per month. This value is really close to the life cycle cost of capacitors. You may be no better off buying and installing your own caps. There are exceptions. Like when you can get a 200kva capacitor bank off ebay for 200$. But if you have to pay for a new capacitor, its a wash because it will take 20 years to pay off.

Originally Posted by adh2000

Whatever power is being used has to go somewhere. Is the transformer hot? 4kW is a lot. If it was really using that it would be too hot to touch. I suppose it takes a little power to make the buzzing noise but that is super minimal most all gets converted to heat.


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It's not power, but "apparent power", or VA. Current at a bad power factor, same thing as a considerable lagging phase. Amounts to much less actual "power", the power is the VA x cosine of phase angle.

Originally Posted by Strostkovy

Are you suggesting having a larger transformer in parallel for large loads that is disconnected when not needed?

Paralleling transformers is doable but can behave unexpectedly when mixing different ones together.

No, just using the small one for the ENTIRE 120 load (which is assumed to be much smaller), and leaving the 208/120 large one for the machine loads only.

[QUOTE=JST;3649277]It's not power, but "apparent power", or VA. ...

AKA 'imaginary' power.

Nearly all US commercial users are charged non-imaginary dollars for this.

I would expect reactive power to get charged at about 1/5th the cost or less of real power.

It would be really helpful if we had a (redacted) copy of the bill to know what is actually being charged for.

I would be more suspicious of aircon, ventilation, hot water, and other standing loads. Have you verified that there is no load leaving the transformers? Not all your loads will be in 'the shop'.

Originally Posted by JST

It's not power, but "apparent power", or VA. Current at a bad power factor, same thing as a considerable lagging phase. Amounts to much less actual "power", the power is the VA x cosine of phase angle.




No, just using the small one for the ENTIRE 120 load (which is assumed to be much smaller), and leaving the 208/120 large one for the machine loads only.

That could be a lot of rewiring. I can't imagine it would cost anywhere near as little as he is being billed for over several years

Originally Posted by SomeoneSomewhere

I would expect reactive power to get charged at about 1/5th the cost or less of real power.

It would be really helpful if we had a (redacted) copy of the bill to know what is actually being charged for.

I would be more suspicious of aircon, ventilation, hot water, and other standing loads. Have you verified that there is no load leaving the transformers? Not all your loads will be in 'the shop'.

Air compressors are also notorious for sucking amps. People tend to not realize how leaky their plumbing has gotten.

Yes, air compressors chew through power. Building services in general tend to not be noticed. Your shop lighting could well be 4kW alone.

The other risk with loads like air compressor is that they cycle, and you might not be measuring while they're on.

Originally Posted by Strostkovy

That could be a lot of rewiring. I can't imagine it would cost anywhere near as little as he is being billed for over several years

That's possible. He'd have to figure that out. He'd need the transformer, a panel for the office, and labor, plus enough wire to make the connections.

Totally depends on what he is getting dinged at.

I assume the office power on the separate one, shop lights etc where and as they are. That way the shop transformers can be totally off.

Another alternative is to shut down the 240 transformer (assuming the 208 is used for 120V) when not in use. That costs nothing, so it would have to have a saving, assuming there is a switch for it.

Just add kvar caps and call it a day, no rewiring needed...Phil

[QUOTE=SomeoneSomewhere;3650537]I would expect reactive power to get charged at about 1/5th the cost or less of real power.

Maybe where you are. Your statement does not hold in the US for commercial customers.

Most I can see are bundled into the demand charges as per-KVA, not a purely per-kVArh charge.

This makes a fair bit of sense as reactive power is only really expensive when your network is nearing capacity.

It also means that attempting to reduce quiescent reactive current draw on transformers is relatively useless as that power factor will improve substantially the moment you start using significant power.

It is going to depend on precisely how OP's bill is calculated.

Originally Posted by SomeoneSomewhere

It also means that attempting to reduce quiescent reactive current draw on transformers is relatively useless as that power factor will improve substantially the moment you start using significant power.

It is going to depend on precisely how OP's bill is calculated.

And, on whether the transformer in question is pulling power during a lot of non-usage hours.

We had a guy on here a few years back who had a big vacant mill building that had a 750kVA or so transformer sitting there idling 24/7/365, pulling quite a bit of VA, and apparently really racking up the charges. It might have had 4 or 5 small lights as a load.

Correct me if I'm wrong but the low power factor draw is due to the inductance of the transformer and is there regardless of load. I just gets swamped out by the draw of the real load.

Using capacitors to cancel out the measured inductance will be the simplest way to eliminate reactive losses. You still have resistive losses due to the inductive current however.

Originally Posted by Strostkovy

Correct me if I'm wrong but the low power factor draw is due to the inductance of the transformer and is there regardless of load. I just gets swamped out by the draw of the real load.

Using capacitors to cancel out the measured inductance will be the simplest way to eliminate reactive losses. You still have resistive losses due to the inductive current however.

Correct on all points.

It gets more complicated at non-UL voltages. That mill transformer probably had an input of at least a 4160V (wye) line, or higher, and it can get expensive to add correction caps. In that sort of case it might be cheaper to drop the service and if needed, have a low voltage single phase one put in for lights. "Or just hit the switch", unless the lights are required.

I'm curious if capacitors on the output side of the transformer can correct the power factor, though at a potentially considerable real power cost.

Originally Posted by Strostkovy

I'm curious if capacitors on the output side of the transformer can correct the power factor, though at a potentially considerable real power cost.

No significant kwh cost to doing so, but the no load losses in the transformer will increase slightly. If the transformer is 98% efficient then for every 1kvar of capacitors you will be losing 10 watts in the transformer (the other 10 watts being iron losses), or 20$ a year at 11 cents per kwh.

If the demand charge is 50 cents per peak kva then its worth it.

Originally Posted by SomeoneSomewhere

Most I can see are bundled into the demand charges as per-KVA, not a purely per-kVArh charge.
This makes a fair bit of sense as reactive power is only really expensive when your network is nearing capacity.
It also means that attempting to reduce quiescent reactive current draw on transformers is relatively useless as that power factor will improve substantially the moment you start using significant power.
It is going to depend on precisely how OP's bill is calculated.

The last statement is 100 percent true.

In the US, most utilities charge for reactive power, because they need to size the transmission network to account for it. Therefore they punish reactive power consumption, for commercial customers only. Theory being that residential customers don't use much ever (not accounting for asshats like me with a 5 hp rotary converter) so they don't bother with KVAR metering. They also do not use peak demand charges for residential customers - again theory being their power use is relatively constant over time.

Commercial users are again socked with demand charges - because their usage is likely to be keyed to time of day, but utilities need to install transmission gear sized to the *peak* of what is used. So commercial users are given an incentive to keep their average, and peak demands, similar in size.

Originally Posted by jim rozen

Theory being that residential customers don't use much ever (not accounting for asshats like me with a 5 hp rotary converter)

Hey now, Jim- that's rapidly approaching out'a line... Just because I don't run a rotary converter often, doesn't exclude ME from being an asshat too... ;-D

Originally Posted by jim rozen

The last statement is 100 percent true.

In the US, most utilities charge for reactive power, because they need to size the transmission network to account for it. Therefore they punish reactive power consumption, for commercial customers only. Theory being that residential customers don't use much ever (not accounting for asshats like me with a 5 hp rotary converter) so they don't bother with KVAR metering. They also do not use peak demand charges for residential customers - again theory being their power use is relatively constant over time.

Commercial users are again socked with demand charges - because their usage is likely to be keyed to time of day, but utilities need to install transmission gear sized to the *peak* of what is used. So commercial users are given an incentive to keep their average, and peak demands, similar in size.

Totally agree.

Years ago I was on a project adding a second office complex to the existing complex. I understood the power charges and made them feed both of the complexes with one feed. This saved us many of thousands of dollars a year in demand charges. The electricians and project manager were not happy with me but it saved us real money. Existing complex had labs and was way over capacity with the feed. Had two transformers and one would have been adequate.

You need to understand how you are billed............. Worrying about the no load VAR costs of a transformer to me is utter nonsense.