A synchronous motor with a synchronous reactance of 12 ohms is operating with a current of 100 A at unity power factor supplying power to a large compressor. The phasor diagram for this operating condition is shown in the figure.
a) The field current is to be adjusted to bring the machine to a new operating point having 60 A of leading current and, since no change is to be made to the compressor, the power input and the100 A of in phase current will remain the same. Sketch the new phasor diagram for this condition on the diagram below, clearly showing the location of the tip of the new I and the tip of the new E.
b) Based on your phasor diagram, find the new values for the amplitudes of the current I and the internal voltage E.
c) With the machine running as in the original phasor diagram, what will be the current and power factor if the compressor load is reduced to zero without any change in the field current? Sketch a phasor diagram for this condition.