Superconducting synchronous machines are designed withsuperconducting field windings which can support large currentdensities and create large magnetic flux densities. Since typicaloperating magnetic flux densities exceed the saturation fluxdensities of iron, these machines are typically designed withoutiron in the magnetic circuit; as a result, these machines exhibitno saturation effects and have low synchronous reactances.

Consider a two-pole, 60-Hz, 13.8-kV, 10-MVA superconductinggenerator which achieves rated open-circuit armature voltage at a field current of 842-A. It achieves rated armature current into athree-phase terminal short circuit for a field current of226-A.

a) Calculate the per-unit synchronous reactance.

Consider the situation in which this generator is connected to a13.8-kV distribution feeder of negligible impedance and operating at an output power of 8.75-MW at 0.9 power factor lagging.Calculate:

b) the field current in amperes, the reactive-power output in MVA,and the rotor angle for this operating condition.

c) the resultant rotor angle and the reactive-power in MVA if the field current is reduced to 842-A while the shaft-power supplied by the prime mover to the generator remains constant.