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

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 $$$.