HV ckt breaker fault rating
HV ckt breaker fault rating
(OP)
Folks,
Got a question on rating a HV circuit breaker.
Say the fault the breaker sees, as calculated by ASPEN, is:
ISC=54597.4 Amps
3LG_AMPS=60602 Amps
For a given X/R=38.4.
Question: What is the minimum interrupter rating (both symmetrical and asymmetrical) for a breaker to interrupt this fault. Assume that the breaker contact parting time is 2 cycles and interrupting cycle is 3.
Minor discussion:
I am assuming 3LG_AMPS is the symmetrical fault current calculated by multiplying ISC by a factor obtained from IEEE std C37.010 (figure 8) since the X/R is higher than 15. Is my assumption correct?
Then how do you get asymmetrical value from this?
I thought this would be a topic that is already explored but I just couldn't find a directly related topic when I searched the forum.
Got a question on rating a HV circuit breaker.
Say the fault the breaker sees, as calculated by ASPEN, is:
ISC=54597.4 Amps
3LG_AMPS=60602 Amps
For a given X/R=38.4.
Question: What is the minimum interrupter rating (both symmetrical and asymmetrical) for a breaker to interrupt this fault. Assume that the breaker contact parting time is 2 cycles and interrupting cycle is 3.
Minor discussion:
I am assuming 3LG_AMPS is the symmetrical fault current calculated by multiplying ISC by a factor obtained from IEEE std C37.010 (figure 8) since the X/R is higher than 15. Is my assumption correct?
Then how do you get asymmetrical value from this?






RE: HV ckt breaker fault rating
RE: HV ckt breaker fault rating
RE: HV ckt breaker fault rating
I'm not familiar with ASPEN breaker duty calcs, so I don't know why 3LG_AMPS is different than Isc.
The ANSI breaker duty also requires/allows adjustments for local generation versus remote source and other factors, breaker contact parting time, etc.
As you say, if the actual system X/R ratio exceeds the test basis for the circuit breaker symmetrical rating, the SC rating of the breaker may need to be reduced.
The best resource for the theoretical basis for the ANSI breaker duty calcs is the book by Conrad St. Pierre "A Practical Guide to Short-Circuit Calculations".
David Castor
www.cvoes.com
RE: HV ckt breaker fault rating
ASPEN aside, if I have a Symmetrical current and X/R over 17, then I need to multiply this by that X/R multiplier obtained from figure 8 of IEEE c37.010 right? How do you get Asymmetrical value then?
RE: HV ckt breaker fault rating
The equation to convert rms fault current to asymmetrical is in ANSI C37.010, I believe. It's an exponential function and not something that easily be written in ASCII.
If you have access to the IEEE Red Book, you should find some additional guidance there. This is not as straightforward as one might think.
David Castor
www.cvoes.com