The news reports on the blackout (now a week old) are really uninformative as to what has really failed. Something like 12 of 22 feeders in a large area of Queens New York City failed. And reports that "low" voltage (120V) lines got overloaded trying to supply the power that the failed feeders normally would handle. I don't thaink that that is correct, usually such low voltage circuits are fed by separate transformers (like "ploe pigs") and feed a few houses each. And these are not normally interconnected. So power could not "bypass" a failed feeder, overloading the low voltage circuit causing it to literally burn up. But I saw news footage of what looked like a low voltage cable literally arcing over and burning up.
Lots of news time spent showing angry powerless customers (I'd be mad too with many days without power) but no simplified esplinations of what the system looks like and what failed.
In a nutshell, Burke explained, the genesis of the outages was the failure of 'feeder lines' that carry 27,000 volts of electricity through ConEd`s 57 distribution areas. Feeder lines connect to transformers that 'step down,' or reduce the voltage down to the 120 volts found in household outlets.
The system is resilient enough that if two and even three primary feeder lines in a service area fail, there will be enough backup capacity to keep power flowing to the point that consumers don`t even notice it.
Last week, however, the Queens distribution area lost about half of its 22 primary feeders for reasons that were still unclear Sunday.
'We lost at least 10 feeder lines,' Burke noted. 'It`s something I have never seen before.'
The loss of feeder lines was blamed for the Washington Heights outages, which according to a report by the New York State Attorney General was traced in large part to insulation issues in the oven-like environment of underground utility vaults.
But as it did in 1999, the loss of the feeder lines in Queens caused higher volumes of electricity to run through the remaining feeders, transformers, and the lower-voltage lines, which were subsequently fried one-by-one by heavy power loads that they simply were not designed to handle.
Speculation here, but what probably caused the low voltage lines to fail was not a cascade failure, but simply brownout conditions dropped voltage levels which caused large A/C motor loads to draw increasing levels of current, overloading low voltage lines and transformers and causing their insulation to fail. I'm perplexed as to why OCP didn't protect the cabling- were these all unprotected tap feeders? I expect you'll have a lot of these type repairs, too, once the power comes back and people discover their A/C and elevators still don't work!
[This message has been edited by SteveFehr (edited 07-25-2006).]
#67949 - 07/25/0607:16 AMRe: Any linemen here know the real story with the Queens NY blackout?
Interesting reading, thanks for that wa2ise. Didn't hear anything in our news about it though. POCO's do have LV tiepoints so they can close links or fuses in case one or two transformers are out of service without immediate loss of power. But with 22 feeders out it is simply impossible to backfeed that through the 120 Volts system. It may have been possible that a major LV tie point was closed somewhere between two big transformers and that caused some smoke and melting of cables, which the media always like anyway to spice up their story. But with soaring heat and airco's running 24/7 and all the extra's in the majority of houses the electricity grid is well and truely overloaded in a lot of big cities around the world.
The product of rotation, excitation and flux produces electricty.
#67950 - 07/25/0611:31 AMRe: Any linemen here know the real story with the Queens NY blackout?
I think this is just the symptom of our crumbling inner city infrastructure. I imagine a lot of this equipment is pre-WWII and has been patched, jumpered out and generally ignored until it failed.
<opinion bit on> This is just an HO guage version of the 77 blackout. Something failed and when they started switching loads around trying to save as many customers as possible, they took out other marginal parts of the plant, until the whole thing was fried.
#67951 - 07/25/0603:17 PMRe: Any linemen here know the real story with the Queens NY blackout?
I was under the impression that the '77 blackout was due to overloaded lines moving power towards NYC, and ConEd dispatch refusing to start up additional generators, when warned of possible thunder storms in the area of the overloaded lines. The storms caused the line(s) to trip, and NJ gave ConEd 1 minute to unload the cross bay feeder. When ConEd could not or would not, ...
Boom, Boom, out went the lights.
Please correct me if I am wrong.
#67952 - 07/25/0605:05 PMRe: Any linemen here know the real story with the Queens NY blackout?
'If the customers don`t see what is going on, they don`t reduce their (power) consumption,' Burke said. 'The electricity went through fewer and fewer primary feeders, which caused them to fail. The low-power grid now has to be put back together.'
Like trying to fit 2 gallons of water in a 1 gallon pitcher.
#67954 - 07/25/0607:46 PMRe: Any linemen here know the real story with the Queens NY blackout?
What they had was an underground networked distribution system, built back in the 50's when the expresways were being built, they changed from area distribution, to networked, which is less expensive to install, when a wide area is involved, the concept is good, as long as it is upgraded for additional loads, however networked systems are more expensive to upgrade, there are are still streets in that area where on one side you have networked 120/208, and on the other side of the street, area distribution at 120/240.
Looks like reinvestment in the system, never happened, what's new!
[This message has been edited by LK (edited 07-25-2006).]
#67955 - 07/26/0610:01 PMRe: Any linemen here know the real story with the Queens NY blackout?
How does the POCO like Con Ed even get the chance to update such equipment without having a few customers off-line? It seems like such a HUGE JOB. But something like this is just a reminder of how important the work we do is. Hundreds of millions of people depend us daily.
#67956 - 07/27/0602:19 AMRe: Any linemen here know the real story with the Queens NY blackout?
I'll try to word this as carefully as possible, but:
It seems that years of POCO's (everywhere) deferred upgrade programs are finally catching up to reality. It was reported on the news today here in So Cal that in some locations, new transformers were burning out in about an hour after being replaced!! I take that to mean that the replacements being installed were of the same kVa as the originals (some dating back into the 1950's.)
Now I don't work for a POCO, but it would seem that common sense would tell me that if a pole pig of say, 25kVa serving 20 or so homes, installed back in the 50's, 60's or even 70's before we have added all these mod cons to our homes, fails, then would it not be more economically prudent to install a pig of the next higher rating in it's place? (Assuming the primary can handle it.)
I for one would not want to explain to the bean counters why we had to replace the same transformers two or more times. The costs in labor and lost revenue have to be far greater than the price difference between the transformers of the next higher rating.
We had one community where the 50's era pig burned out and it took several days (over 5, IIRC) to get them back online!!
Don't get me wrong here, folks, I'm not trying to bash anyone or any POCO!! And the line crews I have met and talked to personally are all great guys doing a difficult and dangerous job!!
But is it not a practice to do load surveys on a utility system, which would tend to help pinpoint potential areas where trouble will be at it's worst? And if so, in my humble opinion that would warrant upgraded transformers at least on a as-failure-happens basis.
These outages all over the country have highlighted (bad pun) how the infrastructure of our nation has been neglected for too long.