ECN Forum Forums General Topics of the Trade General Discussion Area Judgement Call

Our braindead utilities here in CA have come up with another scheme. They plan to drop the supply voltage 3%, claiming they can serve a few more customers that way.
Would it be wise for us to change taps on our 480V customers' transformers, or let them live with their new 116/202 systems? (Can't do anything about the 269/466).
We already get many calls about low voltage problems in the hotter summer months, it seems seldom that the utility is supplying the nominal voltage anyway. I'm concerned about our liability if we make changes. I can see this is going to be a tough summer.

electure;
the call you are contemplating is predeicated on a situation introduced by the utilities. responsibility for any planned as opposed to unplanned power fluctation should be theirs. being that this is a statewide event, i would imagine the Public Service Board assuming you have one not totally seated by power company yes-men should make the 'liability' call here.

Pardon my ignorance once again, but I thought that if you lowered voltage a few percent, some devices will try to make up for the loss by drawing even more current...

And I thought current was the whole problem anyway..... Too much demand, not enough supply... How does decreasing voltage help this situation?

This is probably another one of my dumb assumptions that has nothing to do with the real world...

Here in WV we have the opposite problem. The PoCo likes to run about 122V to 123V per leg, which is real hard on standard 120V light bulbs. I install only 130V bulbs myself because of this.

[This message has been edited by sparky66wv (edited 06-30-2001).]

Virgil, if you're ignorant, I'm worse. I thought the same thing as you. This was on a newsradio station just this week. I don't know more about it than that, but I don't see how it could help. Of course I'm not a power company engineer, either.

Virgil brings up a good point.
We sparky's are all taught the inversley proportional relationship, somehow the math works in their favor...

is there an EE in the house?

[QUOTE]Originally posted by sparky66wv:
[B]Pardon my ignorance once again, but I thought that if you lowered voltage a few percent, some devices will try to make up for the loss by drawing even more current...

I think the key is "some devices". Any resistive loads( incandescent lamps, ranges, water heaters,) will draw proportionally less current.This could really add up. I think inductive lighting will draw more to maintain wattage. Motors, I believe, depending on the type, could go either way.

Are they talking about dropping the voltage 24 hours a day on all lines or maybe in the mornings and evenings in predominatly residential areas where people are using incandescant lighting and electric water heaters. At this time the AC may not be a great percentage of the load. Is 3% on an AC compressor going to draw 3% more current while running at full speed? Also the low voltage starting should draw less inrush; how much of a factor will that be?

Gerald Powell

What we really need to do is enlist the aid of Tibetan lamas to find out who is the present day reincarnation of Nikola Tesla.

I'll try to get more info on this. As I said, it was on the radio just the other day.
I've decided, though, to discourage the retapping of the xfrmrs. When the power monsters realize their trick is a flop, and kick the V back up, I don't want to run around changing the taps again(probably for free).

It seems to me that all devices would draw less current if the voltage is reduced. The only constant here would be the circuit impedance would it not?

Lets say a motor draws 15 amps @ 240 volts for a total of 3600 watts. For the sake of simplicity, the circuit impedance would be 16 ohms. A 3% drop in voltage gives us 232.8 volts. 232.8V ÷ 16 ohms = 14.55 amps, for a total of 3387 watts.

I'm guessing that the only trade-offs will be in horsepower and to a lesser extent, lifespan of the motor.

Matt



[This message has been edited by Matt M (edited 07-02-2001).]