POWER CIRCUIT BREAKERS CAPACITANCE SWITCHING CURRENTS BASICS AND TUTORIALS

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).

3—Circuit breakers with a restrike probability other than the probability of Class C1 or Class C2 are not covered by this standard.

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