tlrols
Electrical
- May 27, 2008
- 75
So, we had a lively discussion at work today regarding when we should use a fault current interrupting device (i.e. a circuit breaker) to serve a load versus something like a circuit switcher or load break switch.
Somehow we have been using the mythical figure of 100 MW of "tapped load" on a 115 kV line to be the "tipping point" for a two breaker scheme to change a line from this(where single line will relay and drop load):
Bus A--brk--line--switch--LOAD--switch--line--brk--Bus B
To this (where only one section will relay, and load is NOT dropped but fed from remaining section):
Bus A--brk--line--brk--LOAD(Bus C)--brk--line--brk--Bus B
Basically our utility has/had deemed it acceptable to "tap" an existing breakered transmission line without using additional breakers to serve load up to 100 MW's or so. We use load break switches to do this.
This of course means that load will be lost for an N-1 contingency. Given the NERC Reliability Standards we now have to declare this stuff a "Local Network Customer" for this load loss to be acceptable.
I know there are many ways to evaluate this. I am wondering what other people's "rules of thumb" might be, if any. I, myself, never saw a breaker I didn't like, but in a cost constrained environment some times you get pressured into using a switch in place of a breaker...
Somehow we have been using the mythical figure of 100 MW of "tapped load" on a 115 kV line to be the "tipping point" for a two breaker scheme to change a line from this(where single line will relay and drop load):
Bus A--brk--line--switch--LOAD--switch--line--brk--Bus B
To this (where only one section will relay, and load is NOT dropped but fed from remaining section):
Bus A--brk--line--brk--LOAD(Bus C)--brk--line--brk--Bus B
Basically our utility has/had deemed it acceptable to "tap" an existing breakered transmission line without using additional breakers to serve load up to 100 MW's or so. We use load break switches to do this.
This of course means that load will be lost for an N-1 contingency. Given the NERC Reliability Standards we now have to declare this stuff a "Local Network Customer" for this load loss to be acceptable.
I know there are many ways to evaluate this. I am wondering what other people's "rules of thumb" might be, if any. I, myself, never saw a breaker I didn't like, but in a cost constrained environment some times you get pressured into using a switch in place of a breaker...
