Idc Short circuit Rating for HV Circuit Breaker

[Schwatzernov]

Hi,

I have the question regarding to the HV/MV short-circuit rating of circuit breaker.

According to IEC standard, the following short-circuit rating of circuit breaker will be used in comparison with the calculated short-circuit current to verify whether such CB have sufficient short-circuit capacity or not;

CB Rating;
Symmetrical Breaking Capacity, Ib sym.
Asymmetrical Breaking Capacity, Ib asym.
Making Capacity, Ip
DC Short-circuit capacity, Idc

Calculated Short-Circuit Current;
Symmetrical Breaking short-circuit current, Ib sym.
Asymmetrical Breaking short-circuit current, Ib asym.
Peak short-circuit current, Ip
DC Short-circuit current, Idc

My question lies on the last one, the Idc. Someone said that only the followings are considered in verification of the adequacy of CB breaking capacity ;
Ib sym.
Ib asym
Ip

The Idc is not required by standard to be used in direct comparison between the calculated short-circuit current and DC short-circuit breaking capacity because Idc effect is already included in Ib asym. So comparison is made only the above 3 parameter to justify CB short-circuit capacity.

However someone said that the Idc is also must be used in comparison, so there are 4 parameters to be compared;
Ib sym
Ib asym
Ip
Idc

Can anyone advise me which one is correct ? due to I have one project which I use ETAP to calculate short circuit current and the result shows that all 3 parameters are within CB capacity except Idc which the calculated Idc is higher than the CB Idc rating. So can I conclude that this CB have enough short-circuit capacity ?

Thank you,

Schwatzernov

 

[7anoter4]

The circuit-breaker rating can be determined by consideration of the dc component according to:
High-voltage alternating-current circuit-breakers, IEC 56,1987.See:

http://ieeexplore.ieee.org/iel5/28/18320/00845066.pdf?arnumber=845066.

and also see:

http://www.jmpangseah.com/chapter-8.pdf

You may also consult this paper:
Considerations for applying IEC standards in short circuit calculations and breaker selections in cogeneration plants

http://ieeexplore.ieee.org/Xplore/login.jsp?url=/iel4/5899/15726/00730135.pdf?arnumber=730135

Summary: This paper discusses a recent experience with the utilization of IEC standards 909 and 56 for calculating short circuit currents and selecting medium and high voltage circuit breakers for cogeneration plants. The paper addresses the “near-to-generator” fault category as defined in these standards. Such a category involves decaying AC current components as well as DC current components with relatively large time constants. The paper depicts the relevance of these factors when applied to circuit breaker ratings and the engineering concerns associated with such exercises
Regards