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Author Topic: Re-starting load after domestic AC power outages.  (Read 400 times)
230RN
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« on: January 12, 2019, 04:22:36 AM »

Had a power outage last night about 10 PM, 2500 power customers affected.  Restored about 11:30 PM.  Happens every once in a while.

I wondered about how they handled what must be a tremendous "starting load," what with refrigerator motors starting up, furnaces and heat pumps coming back on, all essentially instantaneously.  There's sometimes a couple of blinks before it comes on steadily, but mostly, bingo, the power's all normal.

Is the supply equipment just that robust to handle the starting load (e.g., all those inductive devices) all at once, or do they somehow dribble out the "ons" in small areas?  I've never been in a position to see if that's the way they do it.

That's always been a question in the back of my mind.

Terry, 230RN
« Last Edit: January 12, 2019, 04:39:04 AM by 230RN » Report to moderator   Logged
Doggy Daddy
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« Reply #1 on: January 12, 2019, 10:08:06 PM »

I think everyone is waiting to see if you do another edit to fix that one last thing before we reply.
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Fly320s
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« Reply #2 on: January 13, 2019, 02:44:27 AM »

Looks like the answer is, ôgradually.ö

https://en.m.wikipedia.org/wiki/Black_start
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brimic
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« Reply #3 on: January 13, 2019, 06:34:16 AM »

I had a black out a year or so ago- Ĺgraduallyĺ was how the power came back on. The lights came on very dim and full power wasnĺt established for about an hour.
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Ben
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« Reply #4 on: January 13, 2019, 06:43:19 AM »

I had a black out a year or so ago- Ĺgraduallyĺ was how the power came back on. The lights came on very dim and full power wasnĺt established for about an hour.

I've only had that "gradual" thing happen once, after a local eight or so hour blackout close enough to the house that with binos, I could see the crews working on the transformer. With all other blackouts, it has been almost immediately full power.
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« Reply #5 on: January 13, 2019, 07:28:41 AM »

I've only had that "gradual" thing happen once, after a local eight or so hour blackout close enough to the house that with binos, I could see the crews working on the transformer. With all other blackouts, it has been almost immediately full power.

Gradual,  in this case, isn't normally a gradual increase in voltage, but more like you shutting every breaker in your box off when you switch to generator, then flipping the gen breaker, followed by flipping each individual breaker one by one, letting the generator settle at a new level with each flip.

Except the power company flips whole neighborhoods.
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Nick1911
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« Reply #6 on: January 13, 2019, 08:17:56 AM »

I would expect that just connecting the distribution transformers across the line creates a pretty big inrush spike.  I have a 5KVA transformer setup for step-up, it will trip a 20A 240V breaker connected across the line, without any load on the output side.
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AmbulanceDriver
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« Reply #7 on: January 13, 2019, 09:29:28 PM »

I would expect that just connecting the distribution transformers across the line creates a pretty big inrush spike.  I have a 5KVA transformer setup for step-up, it will trip a 20A 240V breaker connected across the line, without any load on the output side.

Can you imagine the current spike switching this beast on? 120MVA

https://youtu.be/VKLsWW4gym8
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« Reply #8 on: January 13, 2019, 10:05:19 PM »

Had one recent outage onage that was intermittent and was dropping out a leg of the three phase. Only know this because our giant air compressor was trying to eat itself and the vent motors on the roof were trying to spool up to about 2 rpm. Luckily someone got all our CNC shut down with no losses. Of course this was no planned restoral, just ice laden pine trees detonating on the wires because somebody didn't have e the time or money to do right of way maintenance, but plenty of money to pay out of state crews to fix it all.  rolleyes
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MechAg94
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« Reply #9 on: January 14, 2019, 12:45:22 PM »

By gradually, I was thinking of turning it back on neighborhood by neighborhood.  Using their local substation switches where possible. 
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« Reply #10 on: January 16, 2019, 09:13:09 AM »

By gradually, I was thinking of turning it back on neighborhood by neighborhood.  Using their local substation switches where possible. 


I believe that for a large enough outage, they will use that approach. 
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MechAg94
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« Reply #11 on: January 16, 2019, 09:28:40 AM »

I was thinking about work.  When we start one of the 15KV motors, we have to call and let the local power dispatch guys know we are doing it. 

In my area, I imagine there are enough big industrial electrical loads that neighborhood low voltage stuff wouldn't stress the system. 
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Brad Johnson
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« Reply #12 on: January 16, 2019, 09:38:52 AM »

Had a mini-discussion about this with a friend who works for the local power company. According to him they roll everything out on a "flows downhill" basis. Make sure the generating station is stable and operating normally, then begin energizing the system in a main lines > substations > zone switches > neighborhood switches order with critical community services getting priority.

He said they are looking at tech that will allow them to discretely energize circuits at the meter level. This would let them get the core circuits back on line much faster since there will basically be no load other than the system's own equipment. They could then energize individual meters on a rolling basis, essentially a soft start for the entire grid.

Brad
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