The rated system-source short-circuit breaking current is the highest system-source short circuit current at contact separation, which the generator circuit-breaker shall be capable of breaking under the conditions defined in standard. Such a current is found in a circuit having a power-frequency recovery voltage corresponding to the rated voltage of the generator circuit breaker and having a transient recovery voltage equal to the value specified in standards.
The rated system-source short-circuit breaking current is characterised by two values:
a)the r.m.s. value of its a.c. component Isc;
b)the d.c. time constant of the rated system-source short-circuit breaking current.
Typical asymmetrical system-source short-circuit current curve shown in figure
AA’,BB’: envelope of current-wave
BX: current zero line
CC’: centre line of the envelope of current-wave
EE’: instant of contact separation.
Imc: peak value of making current
Iaccs: peak value of a.c. component of current at instant of contact separation,EE’
Idccs: d.c. component of current at instant of contact separation, EE’
Source: IEC/IEEE 62271-37-013
