EE3405 Electrical Machines 2 Important Questions
Unit 1
- With neat diagram, describe the construction and working of alternator.
- Discuss the parallel operation of two alternators with identical speed/load characteristics.
- Describe the parallel operation of three phase alternators with help of a neat diagram.
- Explain the principle and construction of synchronous generator with neat diagram. Derive its emf equation.
- 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.
- 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
- 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.
- 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.
- Explain briefly the constructional features and principle of operation of three-phase synchronous motor.
- What is the need for starters? Explain various methods used for starting a synchronous motor.
- Discuss the starting methods of synchronous motor.
- Describe the method of finding out the “V and inverted V” curve with neat sketch.
Unit 3
- Describe the construction of circle diagram of an induction motor and explain how maximum torque is obtained.
- Draw and explain the torque-slip characteristics of cage and wound rotor motor. Also derive the expression for the maximum running torque.
- Sketch and Explain the torque slip characteristics of 3 phase cage and slip-ring induction motors. Show the stable region in the graph.
- Discuss the different power stages of an induction motor with losses.
- Explain the working of synchronous induction motor with a schematic diagram.
- Explain the construction, working principle and parts of three phase induction motor.
- Discuss how the circle diagram is constructed through the No load and blocked rotor tests in three phase Induction motor.
Unit 4
- With neat circuit explain the Static Scherbius system of slip power recovery scheme. Also state the merits of Scherbius system over Kramer system.
- List the various methods of starting of 3 phase induction motor and discuss any two methods of starting in detail.
- Discuss the various starting methods of induction motors.
- Discuss the cascade operation of induction motors to obtain variable speed.
- Explain the Rotor resistance starter in 3 phase Induction motor with neat sketch.
- Briefly discuss the operation of Static Kramer’s and Static Scherbius drives with neat sketch.
Unit 5
- Single phase induction motor is not self-starting. State the reason and explain about the double revolving field theory.
- Describe the constructional features and principle of operation of hysteresis motor and AC series motor.
- List out the classification of single phase motors. Explain any two types of single phase induction motors.
- Discuss the construction, operation and characteristics of the following:
(i) Repulsion motor.
(ii) Servo motor. - Discuss the concept of Double field revolving theory with neat sketch.
- Discuss the operation of Linear induction motor with neat sketch.