We keep our transmission and distribution breakers maintenanced and tested and don't allow the stickiness you evidently are seeing.Its not malfunctioning. Its been documented in event data. Even in stability reports its assumed 2 extra cycles for a 3 cycle breaker and 1.5 extra cycles for a 2 cycle breaker. PJM, ISO-NE, Ercot, ect assume these extra few cycles for a breaker in stability reports involving critical clearing time. Yes these are transmission breakers, but it still holds true for distribution breakers.
Depends on reach. You would normally want your relay to look further and catch those bolted faults. I wil normally set the instantaneous to see 80% of the main line. I will stop at a recloser if it is catching the remainder.If the relay is set to trip instantaneously for this type of fault. Add a few reclosers in series and you are "stacking" curves. Fuse blowing in fuse saving schemes will also increase the time.
Sounds like it is time to tweak the budget.Still more then 5 cycles for that old oil dinosaur.
We use alternate (faster and no reclosing) settings when working on the line. It may cause a lockout for what would normally be a blink but so be it.If that was the case, then we could safely eliminate all breaker failure. And use normal clearing times in substation worker protection calcs. Not going to happen.
That contractor was fired.Now that is what I would consider a rare enough scenario mitigated by correct maintenance and design- not a stuck breaker.
We assume our breakers will operate during a fault the same way as they did during testing.Yes, if your breaker fail time is less then 72 cycles have at it. But you can't ignore it, nor assume normal high speed clearing.
Hey, it is only money.True- unless you insulate everything phase to phase and use only delta loads.
But I'm being lazy and want a spoon-fed summary.Already linked it:
Like California.You can hook everything phase to phase and just keep the MGN.
OK. Haven't ran across it yet.But you should know that graph. Its the foundation for which nearly every step potential, clearing time, loop impedance, bonding and grounding mandate is based upon across most of the globe and soon to be for North America. Its already being used by UL to set the basis for industrial GFCIs.
It doesn't and I have not said it did.Ok, for the sake of the argument lets agree on 5 cycle clearing. After all it is very doable. Where in the NESC does it say a bolted L-N fault (on a distribution line) must clear within 5 cycles? That is what I'm trying to get at.