Electrical Machine-II (EX-501) - Important Questions

Explain the construction of DC machines with all its parts and principle of operation with neat diagram.

Explain armature reaction in a DC machine, its cross-magnetizing and demagnetizing effects and effect on commutation, and methods for effective sparkless commutation.

Explain the construction and working principle of a brushless DC motor, including characteristics and applications.

Explain Swinburne's test with circuit diagram and explain how efficiency of a DC shunt machine is determined from it.

What are the methods of speed control of DC motors? Explain them with neat sketches.

Describe three-point and four-point starters for DC motors, including drawbacks of three-point starter, with neat sketch.

Classify DC motors and explain with sketches their speed-current, speed-torque and torque-current characteristics.

Derive the emf equation of an alternator and explain the meaning of distribution factor and pitch factor.

Explain the synchronous impedance (EMF) method for determining voltage regulation of an alternator.

A 3-phase star-connected alternator has per-phase resistance and synchronous reactance with given load current, voltage and power factor. Calculate the voltage regulation by synchronous impedance method.

Explain Blondel's two-reaction theory of salient-pole synchronous machine with phasor diagram and equivalent circuit.

Draw the phasor diagrams of a salient-pole synchronous generator supplying lagging, leading and unity power factor loads.

Two alternators A and B running in parallel share a given total kW load. Given their kW ratings and speed regulation from full load to no load, determine the load shared by each alternator.

Explain hunting phenomenon in synchronous machines, its causes, and role of damper winding and other damping methods to reduce it.

Explain why a synchronous motor is not self-starting and describe the methods for starting it, including auxiliary motor starting and damper winding induction motor action.

Explain V-curves and inverted V-curves of a synchronous machine, including experimental determination with diagram.