In the circuit of Figure 1, V = 277 volts, L = 2 mH, R = 0:4 ?, and ? = 2 ? 60 rad/s. Determine (a) the rms symmetrical fault current; (b) the rms asymmetrical fault current at the instant the switch closes, assuming maximum dc offset; (c) the rms asymmetrical fault current 5 cycles after the switch closes, assuming maximum dc off-set; (d) the dc offset as a function of time if the switch closes when the instantaneous source voltage is 300 volts.

Figure 1

Current in a series R?L circuit with ac voltage source

e(t) = 2V sin(wt + a) e(t) + -- www R L (t) Swt = 0 lac (2) D wt