Between midnight Tuesday and noon Wednesday, we repaired and restored one feeder but subsequently two additional feeders went out of service. For 97 minutes, between 11:33 and 13:10, 10 of the 22 feeders were out of service. We made repairs through the afternoon and evening, restoring three feeders by midnight. On Wednesday night, as crews continued to repair and restore the primary feeders, the number of feeders out of service declined to seven shortly after midnight Thursday morning and to three feeders out of service at 13:48 on Thursday. The primary feeder system was restored to its design condition at 06:38 Friday when a feeder was restored to service. By 08:01 Friday morning, all feeders were returned to service. Nonetheless, the series of feeders out of service caused damage to the 120/208 volt secondary grid, which resulted in outages to approximately 25,000 customers.
About what size are these feeders?
#68342 - 08/04/0608:42 AMRe: New York July 06 Preliminary Report
The graphic entitled "MANHOLD FIRES AND EXPLOSIONS" caught me offguard though- I think that's pretty indicitive of something being NOT GOOD:
From Monday, July 17, to Friday, July 21, there were a total of 91 manhole events in LIC network – two manhole explosions and 16 manhole fires, as shown in Figure 13, and 73 smoking manholes, as shown in Figure 14.
#68343 - 08/04/0609:00 AMRe: New York July 06 Preliminary Report
Steve, Remember that in NYC, the manholes are generally in the middle of the street, and are exposed to wintertime salt, snow and other contaminants. The manholes can contain lots of different types of stuff, including medium and low voltage feeders, transformers and these really ornery rats.
#68344 - 08/04/0604:29 PMRe: New York July 06 Preliminary Report
I, too, was fascinated by that report, because I was not even aware of the secondary-grid concept -- I had thought that all distribution was radial. Those 120/208 secondary grid conductors must be huge to span city blocks, and locating which transformers are back-feeding a failed feeder must be a real challenge.
ShockMe77, you may have gotten to this part by now, but the feeders are 27 kV with maximum current ratings in the 600 to 900 amp range.
My hat's off to the guys that keep this stuff working.
#68345 - 08/04/0610:22 PMRe: New York July 06 Preliminary Report
I was fairly surprised when I noticed there are about 12-15 houses sharing 3 transformers in my neighborhood. They have them spaced normally down the street but the secondaries are all connnected in each set. I guess it is a way to deal with diversity in a place where we had a lot of snowbirds. I am starting to wonder if that will be causing problems now that we have more year round residents. You know that as soon as one of them goes the rest will go.
#68346 - 08/04/0611:05 PMRe: New York July 06 Preliminary Report
I normally do light residential repair, and telecom, so this is for me not a "newbie" question, just curious. How large a cable (or cables) would one need to supply 900A? It seems that at that high an amperage the cables could get mighty unwieldy...
#68348 - 08/05/0605:07 PMRe: New York July 06 Preliminary Report
A scientific wild a$$ guess (SWAG) based on television news footage, those cables look to be 2 1/2 to 3 inches diameter (outer jacket size). Cable suitable for underground 27KV usually is constructed with the main high voltage conductor in the center, then the insulation, and then there is a metallic jacket that is grounded, and then some more insulation. Like coax cable. The purpose of the outer metallic jacket is to maintain a uniform electrostatic field thru the inner insulation. To avoid sharp points of electrostatic field that could lead to corona breakdown.
#68349 - 08/05/0606:22 PMRe: New York July 06 Preliminary Report