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Question #1: Two identical synchronous machines, each rated 60 MVA, 15 kV, with a sub-transient reactance of 0.1 pu, are connected through a line of reactance 0.1 pu on the base of the machine rating. One machine is acting as a synchronous generator, while the other is working as a motor drawing 40 MW at 0.8 pf leading with a terminal voltage of 14.5 kV, when a symmetrical three-phase fault occurs at the motor terminals. Determine the sub-transient currents in the generator, the motor, and the fault by using the internal voltages of the machines. Choose a base of 60 MVA, 15 kV in the generator circuit.

The given zero sequence matrix is known. .At bus 1 there is a single generator connected with sequence reactance O of. j2 ohms. At bus 2, there are two motors connected, M1 and M2, each with zero sequence reactance of j2 ohms. j2 ohms zero sequence reactance. Motor M2 at bus 2 is solidly grounded.. For these conditions: a. Determine whether or not the generator at bus 1 is grounded. b. Establish the value of the grounding of motor M1. ZBUS (0) Z11 =j 11.42857 Z12 =j 1.42657 Z22 j1.42857 =

A 600 KVA generator with X"a = 0.22 per unit is connected to a bus through a circuit breaker, as shown in the following figure. Connected through circuit breakers to the same bus are three synchronous motors rated 200 KVA, 2.5 KV, 1.0 power factor, with X"a = 0.15 per unit. The motors are operating at full load, unity power factor and rated voltage, with the load equally divided among the machines. (a) Find the rated symmetrical short-circuit current in Amperes, which must be interrupting breakers A and B for a fault at point P. Simplify the calculations by neglecting the Prefault current. M. GHA B