New Family of Relay Curves
New Family of Relay Curves
(OP)
Question, with rule 410 in the 2007 NESC providing a table for PPE cal/cm^2 ratings based on clearing times and fault current availability has anyone heard if microprocessor based relay manufacturers or IEEE standards will develop a new family of relay curves based on the table? In other words, assuming you have 5 cycle breakers, you should be able to develop a curve for a 4 cal/cm^2 system with the correct maximum clearing times at 5, 10, 15 and 20 kA. Same for the 8 and 12 cal/cm^2 levels as noted in the table. If your breakers are faster - all the better. Or, maybe the table is based, in part, on a particular existing relay characteristic?






RE: New Family of Relay Curves
I would be cautious using fast clearing times for breakers unless they have been timed and are well maintained.
RE: New Family of Relay Curves
You will still need to coordinate with downstream recloser and fuse curves.
RE: New Family of Relay Curves
I see at least two papers dealing with arc flash at next month's Western Protective Relay Conference.
RE: New Family of Relay Curves
Thye did this on GE Multilin SR750's. Any of GE/Multilin's microprocessor relays have the capability.
RE: New Family of Relay Curves
RE: New Family of Relay Curves
RE: New Family of Relay Curves
RE: New Family of Relay Curves
My question is perhaps better stated this way:
Does anyone forsee relay manufacturers or the IEEE developing a set of relay curves based on table 410-1 of C2-2007?
Does anyone know from the code standpoint if meeting the required clearing time at the maximum available fault current level meets the intent of the code? An example: I can program a relay with a 9kA instantaneous trip to meet the 8 cal system rating for a 25kV system with a 10kA maximum fault current. This does not mean that the relay clears in the required time at 5kA to again meet the 8 cal system protection requirements. Since we can't guarantee bolted faults how do you set relays as a means to provide "engineering controls" for arc-flash energy management? IEEE 1584 methodology recommends arc-flash energy calculations at multiple fault current levels to determine the "worst case". C2-2007 rule 410 does not seem to address this?
RE: New Family of Relay Curves
In most situations, I suspect that conventional inverse characteristics combined with instantaneous or definite-time elements could do just as well. The upstream and downstream devices probably will have inverse characteristics that would make coordination easier with conventional inverse characteristics.
Using a hot line hold toggle as suggested by stevenal would seem to be a lot easier if coordination during hot line work can be sacrificed. This could be accomplished either by torque control or alternate settings.
RE: New Family of Relay Curves
RE: New Family of Relay Curves
I believe I said "may", it's up to you to determine if and where it's possible on your system. The table doesn't include a 2 cal/cm^2 column, so you would need another method to find the amount of fault current for your instantaneous clearing time.
I've been programming our feeder microprocessor relays as I suggested above since we've used them. The linemen appreciate the fast tripping regardless of the NESC version in effect.
Bolted faults seem to be the rule for these voltage levels per 1584, just look everywhere on the system.