EE3405 Electrical Machines 2 Important Questions

EE3405 Electrical Machines 2 Important Questions

Unit 1

1. With neat diagram, describe the construction and working of alternator.
2. Discuss the parallel operation of two alternators with identical speed/load characteristics.
3. Describe the parallel operation of three phase alternators with help of a neat diagram.
4. Explain the principle and construction of synchronous generator with neat diagram. Derive its emf equation.
5. Derive the generated EMF expression for an alternator. What will be the rms value of emf induced per phase in 3-phase, 6-pole, star-connected alternator having a stator with 90 slots and 8 conductors per slot? The flux per pole is 0.4mWb and it runs at a speed of 1000 rpm. Assume full-pitched coils and sinusoidal flux distribution.
6. How the regulation of an alternator is found using EMF method? A single-phase, 500 V, 50 Hz alternator produces a short-circuit current of 170 A and an open circuit emf of 425 V when a field current of 15A passes. through its field winding. If its armature has an effective resistance of 0.2 ohm, determine its full-load regulation at unity pf and at 0.8 pf lagging using EMF method.

Unit 2

1. Draw the simplified equivalent circuit of synchronous motor and explain the effect of loading in synchronous motor at various power factors with help of phasor diagrams.
2. The synchronous reactance per phase of a 3-phase, star connected 6600 V synchronous motor is 18 2. For a certain load the input is 900 kW at normal voltage and the induced line EMF is 8400 V. Determine the line current and power factor.
3. Explain briefly the constructional features and principle of operation of three-phase synchronous motor.
4. What is the need for starters? Explain various methods used for starting a synchronous motor.
5. Discuss the starting methods of synchronous motor.
6.  Describe the method of finding out the “V and inverted V” curve with neat sketch.

Unit 3

1. Describe the construction of circle diagram of an induction motor and explain how maximum torque is obtained.
2. Draw and explain the torque-slip characteristics of cage and wound rotor motor. Also derive the expression for the maximum running torque.
3. Sketch and Explain the torque slip characteristics of 3 phase cage and slip-ring induction motors. Show the stable region in the graph.
4. Discuss the different power stages of an induction motor with losses.
5. Explain the working of synchronous induction motor with a schematic diagram.
6. Explain the construction, working principle and parts of three phase induction motor.
7. Discuss how the circle diagram is constructed through the No load and blocked rotor tests in three phase Induction motor.

Unit 4

1. With neat circuit explain the Static Scherbius system of slip power recovery scheme. Also state the merits of Scherbius system over Kramer system.
2. List the various methods of starting of 3 phase induction motor and discuss any two methods of starting in detail.
3. Discuss the various starting methods of induction motors.
4. Discuss the cascade operation of induction motors to obtain variable speed.
5. Explain the Rotor resistance starter in 3 phase Induction motor with neat sketch.
6. Briefly discuss the operation of Static Kramer’s and Static Scherbius drives with neat sketch.

Unit 5

1. Single phase induction motor is not self-starting. State the reason and explain about the double revolving field theory.
2. Describe the constructional features and principle of operation of hysteresis motor and AC series motor.
3. List out the classification of single phase motors. Explain any two types of single phase induction motors.
4. Discuss the construction, operation and characteristics of the following:
   (i) Repulsion motor.
   (ii) Servo motor.
5. Discuss the concept of Double field revolving theory with neat sketch.
6. Discuss the operation of Linear induction motor with neat sketch.