1) 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 3 ohms. The input power is 25 kW and the motor has a leading power factor of 0.8.
a) find
i) Calculate the stator reactive voltage drop IXs
b) Draw the phasor diagram for this machine to scale (use graph paper)
i) draw the generated voltage E
ii) Calculate phase current
iii) measure or calculate the magnitude of E
iv) By construction and/or by calculation find the load angle
c) If the excitation is reduced by 10% and, as a consequence the generated emf is reduced by 10%,
i) draw the new phasor for E’ on the same diagram.
ii) measure or calculate the new value of the generated emf E’,
iii) Measure or calculate the new stator current, the power factor and the load angle from the phasor diagram, (assuming that the load does not change).
d) Comment very briefly on the effect that reducing the excitation has on the power factor, stator current and the load angle.