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This topic comprises 2 pages: 1 2
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Author
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Topic: home electrical service question
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Frank Angel
Film God
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Posts: 5305
From: Brooklyn NY USA
Registered: Dec 1999
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posted 01-14-2012 04:46 PM
Basically its the load variation. We experience the same patterns in our theatre that you are seeing, Scott; fairly steady during the day with a significant rise starting around 6pm as large users -- businesses mostly -- begin to shut down. Con Edison explained that regulating and balancing the load on the grid to compensate for the variation isn't easy, evidently. This is what they told us when we found equipment dying premature deaths.
When I put in Furman rack mount power units with a digital read-out in the booths, there was no doubt that the voltage would rise at night. I have seen them sending us a stead 130v for an hour or more before it leveled back down to 127-8, which is not what you'd like to be juicing up your equipment with.
And as much as there are transformers and a rectifier in front of the Peerless lamphouses, the arc burn still reacts to these changes. Starting with the Evening show, you have to start readjusting the carbons and watching them more closely because that voltage increase was enought to get eratic drift, and the dreaded mushroom bubble on the tip of the negative carbon. And that was after they burned rock steady during the first two shows.
And let me tell you, 130v is no picnic for equipment designed to run on 110v-120v. We decided to stop keeping the studio equipment on round the clock and began shuting it down at night when we realized that equipment was meeting some very premature deaths. Also, we'd come into the studio in the morning and two or three of the lights in the hallway would be burned out. We even switched to Long Life Service bulbs and they didn't fare much better.
Con Ed's answer to our complaint was that it was within their parameters of what is considered "normal range" of fluctuation.
On the really expensive stuff, we put Triplite voltage conditioners, but you really can't do that for the big high wattage equipment.
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Tony Bandiera Jr
Film God
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Posts: 3067
From: Moreland Idaho
Registered: Apr 2004
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posted 01-14-2012 06:11 PM
Scott:
Utility standards required by law allow a +10% to -10% long-term variation from the Nominal supply voltage. So for 120v, the high can be 132v and the low can be 108v. Short-term deviation can be 15%.
EDIT: Jason's post went up as mine was being typed..wiki's source is wrong, 10% + or - is the allowable deviation.
As for Frank's problems he mentioned, there should be no failures with well-designed equipment. Sad to say even some major brand names have crappy power supplies that can't handle the normal variations (are you listening, Dolby?) Light bulbs are another story, their quality has been shit for the last several years. The filaments are made of thinner wire, with less tungsten content, and fewer filament supports.
I have several books on, and have studied, power transmission and distribution for many years. Frank, Con Ed wasn't lying to you. In matter of fact, taken in the literal sense, since AC power generation MUST Exactly match demand, in the literal sense the power grid as it exists today is theoretically impossible. The only reason the grid works and survives is that normal load diversity is such a small percentage of the overall imbalance that although it stresses the transformers and generators, the imbalance is not enough to collapse the grid.
But, as the great East Coast (and other) blackouts have shown, unbalance things enough and a major collapse happens.
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Stephen Furley
Film God
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Posts: 3059
From: Coulsdon, Croydon, England
Registered: May 2002
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posted 01-16-2012 02:16 PM
Louis, Where on Earth do you find 140 V bulbs? I know that most of the small decorative ones over there tend to be rated at 130 V, presumably to extend the life of them. I've got some C9 Christmas lights which are 130V for example.
Scott, find out for certain what the tolerances are on your supply, if you're not sure ask the electricity company. If you're regularly seeing Voltages outside this range then report it to the electricity company; it's their problem to sort it out. Do you own or rent the apartment? If you rent then your landlord would probably have to contact them to report it. This assumes that you are fed directly from a transformer owned by the electricity company. If you're not fed directly, for example if the company supply the building at 277/480 V three phase and the owner of the building own a transformer to step this down to provide your supply then you'd have to report it to them. If the incoming supply to that transformer was out of range, then they in turn would have to take it up with the electricity company.
If the Voltage which you're getting is within spec, but you have equipment which can't cope with it then it's your problem, and you would have to install stabilisation equipment to handle it.
I recently had a problem at work. Until recently the Voltage was always low. After our high Voltage feed was moved to a different supply it was always high. Overnight I was seeing Voltages as high as 269.2 V on one phase, and only slightly less on the others; 253 V is the upper limit here now. I collected data from a UPS over several nights, highlighted figures out of range in red, and sent them to the consulting engineers for our refurbishment project. They sent them to UK Power Networks who sent an engineer in late one night to take the tap changer on the transformer down a notch. It's still slightly high, but well within spec.
It's rather different over there with the small pole mounted transformers which you use; I don't think these have tapchangers. Transformers in large substations. over here typically 66 or 33 down to 11 or 6.6 kV, usually have automatic on-load tap changers which adjust to keep the Voltage reasonably constant throughout the day.
All that you can do if it is above the limit is to take it up with whoever owns the transformer which is feeding you; they may in turn have to take it up with somebody else.
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Jeff Stricker
Master Film Handler
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Posts: 481
From: Calumet, Mi USA
Registered: Nov 1999
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posted 01-17-2012 07:06 AM
To correct for power factor (inductive loads like motors, etc being switched on), the power company will switch power factor correction capacitors across the line. These capacitors can be seen up high on poles here and there in the distribution system, and there is usually some type of "controller" mounted low on the pole. This controller senses the line voltage, and if it gets below a certain value, the power factor correction capacitors are switched across the lines. This, in turn, raises the line voltage which, I'm sure, is one of the effects that Scott is noticing.
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