ABSTRACT
This chapter shows that how to compute short-circuit currents in dc circuits with both constant and variable self-inductance. It describes the short-circuit calculations in both ac single-phase and three-phase systems. The chapter discusses asymmetrical and symmetrical short-circuit ac currents to show how phase and load angles affect fault conditions and argues that transient current phenomena must also be considered. The transient affects both the mechanical and the heat-dissipation properties of switching equipment. Switching speed, contact structure, and arc chamber construction are all affected by transient currents. The extent of the ripple present affects the approach used to examine the transient current function. If iron-based components are used in an ac circuit, the self-inductance may vary during the transient. The changing permeability and flux make the time constant different to compute during the transient event. The duration of the transient damping behavior depends on the time constant R/L in the exponential term.
