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).]

Brownouts, or the intentional lowering of voltage, is not supposed to be practiced any more. Thats why they are having rolling blackouts out there.

I suppose that shutting down entire sections of the grid on a rotating basis is a better way electrically to reduce the load, but it doesn't seem safe to me, well neither does lowering the voltage to all those internet places out there. But I would suppose it's the the lesser of the two evils.

I would sell the big diesel or natural gas generators rather than change taps.

I should think that the motors would fare better than most items, as they're rated 115, 200, 230, 460 V

McGraw-Hill's "Electric Motor Manual"
(1987) includes a table that shows undervoltage having the following effects on induction motors:
Increase starting amps
Increase full load amps
Decrease efficiency
Increase power factor
Increase torque

Unfortunately, there is no in-depth explanation.

Redsy,
is there a recommended overall % , or would that be motor make , brand...???

Sparky,
The book states that "induction motors will operate successfully under running conditions at rated load with a voltage variation of 10% at the motor terminals. A frequency variation of 5% is permissible. A combined variation of voltage and frequency of 10% is acceptable provided the frequency doesn't vary by more than 5%(i.e. 7% voltage variation with 3% frequency variation).
Also: the effects of overvoltage are shown:

Starting amps--decrease
Full load amps--increase
Efficiency--decrease
P.F.--decrease
Torque--decrease.

Notice that undervoltage AND overvoltage are shown to increase Full-load amps.

It says that low voltage will cause higher than normal current to the point of over heating.
It also says that a SMALL increase in voltage could reduce current draw, but increases in excess of 10% cause saturation of the iron and a significant increase in current draw with accompanying overheating.

>The PoCo likes to run about 122V to 123V per leg, which is real hard on standard 120V light bulbs.
And I was happy with 125.7 V.

Yeah, I guess we use a little more electric in our light bulbs.

Yeah, after thinking a little more about it I realized that a motor that is rated for 240/208 volts will draw more current at 208 volts than it does at 240, without any change in the wiring. The tables at the end of article 430 show that.

I guess an inductive load like a motor tries to compensate for the drop in voltage to maintain power output? I'm sure this was all covered in one of my classes about 25 years ago or so

Matt

At where I used to work, (which was bought by a cal company) they improved everything but the installed elec dist sys.... R. the (alleged) leading electrician had the following theory.... "I can be out of electricity, I still have open slots in the breaker box"....lol Push came to shove when they tried to install a new "sofisticated electronic testing device" It wanted 480V. (big period) that section of the complex, had been running on 430volts fer the last year or so (due to all the additional equipment installed) The installation tech said if you can't supply me with 480v, than I will have to leave and take the warranty with me", some one called the yahoo from cal who was our new boss, he wanted us to change the taps on the xfmr. I refused citing "just what do you think will happen if they shut down the power users portions of this bldg??
it finally woke them up to upgrading the txu tranformer and switchgear

When I lived in Buffalo, years ago, they had a generating station right on the river(Niagara), and Riverside a subburb of that town, had this problem every summer, it seems the local Power company Niagara Mohawk would divert some power to NYC, and Vio-la brownout, especially refrigerators but that was some 27 years ago, hope its gotten better.

And after all this---nothing. Not a drop in voltage, not a rolling blackout for months.
Nothing but finger pointing, credit grabbing, and $$$.

Assuming the voltages are within tolerance in the first place a 3% drop should not be detrimental. Keep in mind that motors draw more current when operated at an over ANDunder voltage. The reason is counter-electromotive force or back EMF. When voltage decreases back EMF decreases offering less resistance to current. The motor draws more current and runs hot.
When overvoltage is present back EMF is saturated and opposition to current flow is only limited to the maximum back EMF and motor winding impedance. More current flows and the motor overheats.
Inductive loads will draw more current but maybe the ratio of resistive to inductive loads is offset enough it makes it feasible to the utility's.

You have a good point there. The overloading is attributed to air conditioners. The average load surely is not an incadescent light bulb.


[This message has been edited by Dspark (edited 09-05-2001).]

Dspark,

My mention of light bulbs was just a tangent, I in no way was putting the blame on their use...

I was merely stating that I use 130V bulbs because 120V bulbs don't last long around here due to the higher than nominal voltages...

Many uncouth electrical contractors have used this to get entire rewire jobs... When only a bulb change was needed...

130's last 6 months whereas 120's last about 4 weeks... Well worth the difference in cost.

Pardon my digression, it's in my character!...



[This message has been edited by sparky66wv (edited 09-05-2001).]

I've lost the thread, we did have 190/109 + - here in the raging metropolis of Chester VT. We had UPS's quakin', fluor lights flickering, compressors blowing fuses....

the answer i recieved sounded real political.

where are those lama's when ya need 'em..?

Sparky,
I was going back to my original post of a couple of months ago referencing the CA deregulation and the threats of everything from short rolling blackouts to loss of the entire state's production, none of which has occurred.
This thread was brought back up after a couple of months of dormancy.

Are you possibly confusing this thread with
your thread regarding the 190-109 Volt problems you experienced in VT., titled "Brownout?"


[This message has been edited by electure (edited 09-05-2001).]

The rolling black-outs in California even made the BBC News over here.