Breaker Test X/R Ratio
Breaker Test X/R Ratio
(OP)
I would like to inquire as to what X/R ratio medium voltage circuit breakers are generally tested to sustain their S.C. ratings.
Appreciate any help. Thank you.
Appreciate any help. Thank you.






RE: Breaker Test X/R Ratio
In addition, the symmetrical current must be calculated per ANSI standards when evaluating adequacy of breaker ratings versus actual duty.
For IEC, it's even worse
RE: Breaker Test X/R Ratio
Per ANSIC37 or IEC 60271 (now both are harmonised) all general purpose (not used for capacitor switching) MV/ HV circuit breakers are tested for X/R=17 at 60 Hz (X/R=14 at 50 Hz)
If the calculated X/R ratio is greater than 17 at 60 Hz, like at generating stations, then the manufacturer has to be consulted to purchase CBs tested for a higher X/R ratio so that TRV are with in given limits in both ANSIC37/ IEC 60271.
RE: Breaker Test X/R Ratio
I think that is a great oversimplification of the ANSI C37 standards for MV breaker ratings. But I don't have time to do the research now. Low voltage power circuit breakers are rated this way, but I do not believe it is that simple for medium-voltage breakers.
I'd recommend referring to Conrad St. Pierre's book on Short Circuit calculations for a comparison of ANSI and IEC standards. If the medium voltage breaker standards are harmonized, it's news to me and must be recent.
Cheers,
Dave
RE: Breaker Test X/R Ratio
Symmterical Current = 40kA
Close and Latch Current = 108kA (64kA) Peak
There goes 40 x 1.6 = 64kA, 40 x 2.7 = 108kA
It seems that the breaker is sized as per IEEE Std C37.010-1999 (on a Symmetrical Current Basis).
RE: Breaker Test X/R Ratio
Electrical analysis software packages such as EasyPower and SKM can do this ANSI duty calculation automatically.
RE: Breaker Test X/R Ratio
RE: Breaker Test X/R Ratio
LPSs for you guys for succinct replies.
Rafiq Bulsara
http://www.srengineersct.com