ABSTRACT
The heat generation rate and the mechanical force in conductors, being the square function of the current, are the highest at the —rst peak of the asymmetrical fault current. The current then decays to the symmetrical value in several cycles and steady state value in about 1 second, as the generator reactance rises from low subtransient to transient to steady state synchronous reactance value. The mechanical damage is avoided by bracing the structural parts to withstand the —rst peak of the mechanical force without exceeding the allowable stress or de¡ection limits. If that is not possible or practical, the protection system must incorporate a suitable fault current limiting fuse or circuit breaker, or insert a series reactor in the line, to limit the current. The thermal damage is avoided by interrupting the fault, typically in several cycles, before it can overheat the equipment and burn the insulation.
