Total relay time (for a Breaker - Short Circuit analysis)
Total relay time (for a Breaker - Short Circuit analysis)
(OP)
We have to calculate the total relay time (tripping delay) for a 115 kV Breaker for fault analysis.
Let's say primary lead differential relays operate a lockout relay which in turn trips another WL-1 relay for breaker trip.
The results (test conducted a decade ago) we have is as follows:
• A phase A Phase 3.2 cycles @ 160 amps 5.5 cycles @ 600 volts
• B Phase 3.17 cycles @ 160 amps 4.70 cycles @ 600 volts
• C Phase 3.8 cycles @ 160 amps 4.81 cycles @ 600 volts
Question is, do I pick the phase with longest cycle? If yes, since this is 115 kV breaker, do you go with 160 A or 600 V? We are looking at a fault of about 65 kA value.
This in turn trips WL-1 relay which takes about 2 cycles. This means, our total relay time is X + 2, where X is the answer to my above question.
Right?
Answer will be appreciated.
Let's say primary lead differential relays operate a lockout relay which in turn trips another WL-1 relay for breaker trip.
The results (test conducted a decade ago) we have is as follows:
• A phase A Phase 3.2 cycles @ 160 amps 5.5 cycles @ 600 volts
• B Phase 3.17 cycles @ 160 amps 4.70 cycles @ 600 volts
• C Phase 3.8 cycles @ 160 amps 4.81 cycles @ 600 volts
Question is, do I pick the phase with longest cycle? If yes, since this is 115 kV breaker, do you go with 160 A or 600 V? We are looking at a fault of about 65 kA value.
This in turn trips WL-1 relay which takes about 2 cycles. This means, our total relay time is X + 2, where X is the answer to my above question.
Right?
Answer will be appreciated.






RE: Total relay time (for a Breaker - Short Circuit analysis)
The total relay time should be the following
(protective relay time) + (lockout relay time) + (WL relay time)
RE: Total relay time (for a Breaker - Short Circuit analysis)
Keep in mind that these clearing times are MAXIMUMS. Sometimes it will be faster.
Don't forget the time required for the differential relay to operate if you are really getting picky.
David Castor
www.cvoes.com
RE: Total relay time (for a Breaker - Short Circuit analysis)
Assume we don't have the manufacturer's data; what would you do then? Are the current/voltage they are tested at sufficient to give us the relay time? If yes, which phase would we take? Maximum of all three phases?
I agree about addition of the Diff relay's time as well.
RE: Total relay time (for a Breaker - Short Circuit analysis)
If you post the manufacturer and model number, I suspect someone here will have the info or know where to find it.
Obviously you have to use the worst-case. What the worst-case is will depend on what you are trying to calculate. In general, it will be the slowest time, but if you are trying to determine the interrupting duty on the breaker itself, then you also probably need to know the contact parting time.
David Castor
www.cvoes.com
RE: Total relay time (for a Breaker - Short Circuit analysis)
RE: Total relay time (for a Breaker - Short Circuit analysis)
RE: Total relay time (for a Breaker - Short Circuit analysis)