[ i_sc(t) = I_ac \sin(\omega t + \theta - \phi) + \underbraceI_dc e^-t/\tau_\textDC offset ]
Unlike a steady-state current, a short-circuit current has two components: short circuit currents
| Type | Description | Use in analysis | |------|-------------|------------------| | (Initial symmetrical RMS) | RMS current at the instant of fault (subtransient period, first ~10 ms) | Sizing circuit breakers’ making capacity | | ip (Peak make current) | Peak value including DC offset. ( i_p = \sqrt2 \cdot I"_k \cdot \kappa ) where ( \kappa ) depends on R/X ratio. | Mechanical strength of busbars, switchgear | | Ik (Breaking current) | RMS current at contact separation (after some cycles). May include AC decay from generators. | Interrupting capacity of breakers | | Ib (Steady-state short-circuit) | After all transients decay (only synchronous machine excitation remains). | Thermal effect for long-duration faults | [ i_sc(t) = I_ac \sin(\omega t + \theta
Short circuit currents are broadly categorized by their waveform characteristics and the number of phases involved: May include AC decay from generators