Question

A three-phase delta-connected synchronous induction motor is connected to a 415 volt, 50 Hz supply. The winding resistance is negligible and the synchronous reactance per phase is 5 ohms. The input power is 20 kW and the motor has a leading power factor of 0.8.

Draw the phasor diagram for this machine:

ii) use the IXs phasor and the V phasor to construct the phasor for E.

iii) measure or calculate the magnitude of E

iv) By construction and/or by calculation find the load angle

c) If the excitation and, as a consequence the generated emf, is reduced by 10%:

i) Calculate the new value of the generated emf E’

ii) Construct the new phasor for E’’ on the same diagram, using the same value for reactive volt drop

iii) Calculate or measure the load angle iv) Draw the new stator current phasor from the phasor diagram, measure or calculate the new power factor