A synchronous machine is delivering 1.0 pu to an infinite through a double-circuit shown in Figure Q4(b). The direct axis transient reactance of the generator is 0.15 pu. The reactance for each line is 0.5 pu. All reactance is given to a base of the machine rating. One of the transmission lines experiences a solid three phase fault to ground, during which occurrence the system reactance are as shown in Figure Q4(b). a) Write a swing equation during prefault system condition. b) Determine the resultant electrical power equations during fault. c) Compute the critical clearing angle before which the circuit breakers of the faulted line should operate if the stability is to be maintained. (Take inertia H=5MJA/MVA) d) For the same fault in Q4b. (c) above, find the margin of the stability in seconds. E = 1.22 8 pu X = 0.15pu Bus 1 Line 1 Line 2 j0.5 p.u. j0.5 p.u. Figure Q4(b) Bus 2 V=1.0/0 p.u. Grid Infeed