Dear Mr. PoliPoliCarps (Electrical)(OP)30 Jun 20 03:39
Q. " ...thread237-450461: Switchgear Icw and Icu of Circuit Breaker. In reference to the previous closed thread. Should the Icu of the Switchgear be equal to the Icu of the Circuit Breaker? or Vice-versa?...".
A1. Several days had pasted, without any response. I try to answer your question.
A switchgear= ASSEMBLY per IEC may be tested to [Short-time withstand current] say 65kA 1s or say 50kA 3s. The ASSEMBLY is "expected" to withstand the same [kA and duration] for many more occurrence during its service life of say 50+ years. In general, there in no significant change on the busbar mechanical characteristics, bolt and nuts properties, clearance/creepage distances etc. However, [weakening] of the (busbar holders, insulators is expected). Therefore, a say 50+ year ASSEMBLY would be lower in kA and duration.
A2. Icu of the Circuit Breaker is a rating of the breaker. After tested to Icu kA, the breaker is classified into two categories i.e. serviceable at rated value or serviceable at a lower value etc (see IEC breaker Standards).
A3. An ASSEMBLY rating may be > the Icu of the breaker or vice-versa. However, whichever the lower value Shall be higher than the system short-circuit kA rating.
Che Kuan Yau (Singapore)
