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#28283 - 08/15/03 11:57 AM Wild oscillations of line voltage Aug 14th.
wa2ise Offline
Member

Registered: 11/29/02
Posts: 771
Loc: Oradell NJ USA
This afternoon (Aug 14th) just after 4PM the powerline hiccupped. The voltage became unstable, peaking at 147V and dipping to 79V, according to my Kill-a-watt voltmeter, which I believe to be reasonably accurate. At first the line dipped to around 90V, and bounced around 100V. I shut down all the devices with compressors (air conditioners,
fridges and a dehumidifier). Then for about an hour the line would cycle up and down from 95V to 140V. The average period of a cycle was around a half minute. I shut down all the devices with compressors (air conditioners, fridges and a dehumidifier). Then things got more stable, but hot.
Like around 145V! I also unplugged most all electronic loads like TVs, VCRs, and this computer. Now (8PM EDT) the line is
reasonably stable at a normal voltage, 120V. My location is Oradell NJ, Bergen County, northeast NJ, and fed by Public Service Electric and Gas. Oddly enough, back in the blackout of the mid sixties, we did not
lose power then here either. Maybe because the guy who runs the local power plant lives a few houses from here.

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#28284 - 08/15/03 02:02 PM Re: Wild oscillations of line voltage Aug 14th.
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
Interesting that the regulation suffered so badly that way. I wonder if we'll get a full explanation in time?

I see from one news report earlier that U.S. officials are saying the problem originated in Canada, while a Canadian spokesman was pointing the finger south of the border.

"Was your fault!"
"Was not!"
"Was too!"

Sheesh!

[This message has been edited by pauluk (edited 08-15-2003).]

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#28285 - 08/15/03 02:21 PM Re: Wild oscillations of line voltage Aug 14th.
Bjarney Offline
Moderator

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
From msnbc: "...a 300 megawatt eastward flow of electricity quickly reverse into a 500 megawatt flow to the west..."

A classical term for this condition is sub-synchronous resonance. It can be deadly to generator rotors with severe torsional stress.

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#28286 - 08/15/03 02:37 PM Re: Wild oscillations of line voltage Aug 14th.
Bjarney Offline
Moderator

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
The condition is not trivial. System operators {and likely automated systems} have to quickly decide what to do, {or NOT do} and it’s a potential tradeoff between million-dollar generators and million-dollar losses in revenue.

The job has to have moments where a dispatcher would find an air-traffic controller's job to be pure gravy.

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#28287 - 08/15/03 03:12 PM Re: Wild oscillations of line voltage Aug 14th.
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
Bjarney, This might be asking a lot but you seem to be good at making technical things easy to understand.

What causes this "sub-synchronous resonance"

and

Why is getting the grid back up and running such a time consuming proceess?

In other words just turn the switch on already.

Bob
_________________________
Bob Badger
Construction & Maintenance Electrician
Massachusetts

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#28288 - 08/15/03 03:20 PM Re: Wild oscillations of line voltage Aug 14th.
ThinkGood Offline
Member

Registered: 08/07/02
Posts: 1084
Loc: Milwaukee, WI
 Quote:
From msnbc: "...a 300 megawatt eastward flow of electricity quickly reverse into a 500 megawatt flow to the west..."


That almost sounds like the Hippy Dippy Weather Man (George Carlin)

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#28289 - 08/15/03 03:22 PM Re: Wild oscillations of line voltage Aug 14th.
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
 Quote:
"Was your fault!"
"Was not!"
"Was too!"

Sheesh!


I can send my 3 & 5 year olds out as negotiators for this dispute, they have PhDs in finger pointing.

_________________________
Bob Badger
Construction & Maintenance Electrician
Massachusetts

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#28290 - 08/15/03 06:08 PM Re: Wild oscillations of line voltage Aug 14th.
Bjarney Offline
Moderator

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
   Fourmilab map centre: 41°9'N 80°34'W, width 18 degrees

Looking fairly normal?

http://www.fourmilab.ch/cgi-bin/uncgi/Earth




[This message has been edited by Bjarney (edited 08-15-2003).]

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#28291 - 08/15/03 06:28 PM Re: Wild oscillations of line voltage Aug 14th.
Bjarney Offline
Moderator

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
iwire — Sub-synchronous resonance occurs when voltage and current fluctuate at well below normal line frequency—60Hz in the US. Imagine a power system as a huge rotating shaft that stretched across a state. Now, for this to work, every generator {for instance, water wheels} are connected by belts to the giant shaft. Also connected to the shaft with belts are grinding stones that crush wheat into flour. One could have pairs of water wheels and stones, but because river water flows 24 hour a day, it would be nice to be able to get your local water power to other people that could use it when you aren’t. [You could earn money, and the flour mill operator might find it economical to use your water power than to produce his own.]

There needs to be a idler wheel on each belt that connects to the big shaft by tension, so that if there are problems, a piece of rotating equipment can be taken off line to prevent its damage, or possibly damage to the other connected power sources and loads.

Because the big shaft is not perfectly stiff, it has a tendency to twist from torsional forces as various waterwheels and grinding stones operate. Small changes in speed over the shaft length stress the shaft—ideally not to the point of damage, but if allowed to persist could be destructive.

Adding water wheels to the shaft {or removing grindstones} has a tendency to speed up the shaft, where removing water wheels or adding grindstones has a tendency to slow the rotating “system” down.

Does that make any sense?




[This message has been edited by Bjarney (edited 08-15-2003).]

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#28292 - 08/15/03 07:19 PM Re: Wild oscillations of line voltage Aug 14th.
wa2ise Offline
Member

Registered: 11/29/02
Posts: 771
Loc: Oradell NJ USA
 Quote:
Why is getting the grid back up and running such a time consuming proceess?

In other words just turn the switch on already.


You know, when say turning on the air conditioner or similar load, the lights dim for a fraction of a second. A current surge. Multiply that by millions, and I doubt the power system could take it. So you switch on small segments of towns at a time, likely the first up are where your shareholders mostly live.

It might be that the reason I didn't lose power is that the county's water purification and pumping plant is a mile from here, in the next town, and they're on my feeder. To avoid a Cleveland type mess they gave us top priority?

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