Capacitance
switching currents may include part or all of the operating duty of a
circuit breaker, such as the charging current of an unloaded
transmission line or cable or the load current of a shunt capacitor
bank. The rating of a circuit breaker for capacitance current
switching shall include, where applicable,
a) Rated
line-charging breaking current applicable to all outdoor circuit
breakers
b) Rated
cable-charging breaking current applicable to all indoor circuit
breakers
c) Rated single
capacitor bank breaking current
d) Rated
back-to-back capacitor bank breaking current
e) Rated
back-to-back capacitor bank inrush making current and frequency
Preferred
values of rated capacitance switching currents are given in Table 1A,
Table 2A, and Table 3A of ANSI C37.06-2000. The recovery voltage
related to capacitance current switching depends on
— The
grounding of the system
— The
grounding of the capacitive load, e.g., shielded cable, capacitor
bank, transmission line
— The mutual
influence of adjacent phases of the capacitive load, e.g., belted
cables, open air lines
— The mutual
influence of adjacent systems of overhead lines on the same route
— The
presence of single- or two-phase ground faults Two classes of circuit
breakers are defined according to their restrike performances:
— Class C1:
low probability of restrike during capacitance current breaking
— Class C2:
very low probability of restrike during capacitance current breaking
Each
capacitance current switching rating assigned [see item a) through
item d) in this subclause] must have an associated class (i.e., C1 or
C2) with it.
NOTES
1—The
probability is related to the performance during the series of type
tests stated in 4.10 in IEEE PC37.09a and subsequently in 4.10.1
through 4.10.12.
2—A circuit
breaker can be of Class C2 for one kind of application (e.g., in
grounded neutral systems) and of Class C1 for another kind of
application where the recovery voltage stress is more severe (e.g.,
in systems other than grounded neutral systems).
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