EE2251 ELECTRICAL MACHINES – I
PART-B [16MARKS]
UNIT-I
1. Explain the methods of analyzing the magnetic circuits
2. Explain the two types of magnetic circuits with neat diagram
3. Explain in detail about electromagnetic induction
4. Draw the typical B-H curve and hysteresis loop and explain its concepts
5. Explain the meaning of self induced emf, mutually induced emf, statically induced emf, dynamically induced emf and give practical examples
6. Distuingusih between statically induced emf and dynamically induced emf
7. Prove that M=k√L1L2
8. Explain about magnetization curve for Ferro magnetic material
9. Explain in detail about hysteresis loss and eddy current loss in detail
10. Explain various types’ core loss on detail
UNIT-II
1. Explain the construction of a transformer.
2. a. Derive the emf equation of a transformer.(8)
b. Develop an approximate equivalent circuit for a two winding transformer. (8)
3. A 100 KVA 1100/200v single phase transformer has the following parameters.R1 = 1 ,
X1= 3 , R2=0.04 , X2=0.012 . Find the equivalent resistance and leakage reactance as referred to High Voltage winding.
4. a. Discuss about the working principle of a transformer. (8)
b. Draw the phasor diagram & explain the operation of a practical transformer on load. (8)
5. Draw the equivalent circuit of a single phase 1100/220 V transformer on which the
Following results were obtained.
i . 1100V, 0.5A, 55W on primary, secondary being open circuited. (8)
ii. 10v, 80A, 400W on low voltage side, high voltage being short circuited. (8)
Calculate the voltage regulation and efficiency of the above transformer when secondary supply is 100A at 0.8 pf lagging.
UNIT-III
1. Explain the various concepts of magnetic field in rotating machines
2. Explain with neat diagram the concept of MMF space wave single coil
3. Explain the torque production in synchronous machine
4. Explain the concept of electro mechanical energy conversion in detail
5. Explain the concept of singly excited machine and derive the expression for electromagnetic torque
6. Derive the expression for mechanical force developed by magnetic field
7. Briefly explain the multiply excited magnetic field in detail
8. Explain in detail the mmf space wave of three phase distributed winding
9. Derive the torque equation of a round rotor machine clearly stating all the assumption
made give the relation between field energy and the mechanical force developed in the field
10. Derive an expression for co energy in multiply excited magnetic field systems
UNIT-IV
1. a. Derive the emf equation of an alternator. (10)
b. A 3 phase, 12 pole star connected alternator has 72 slots & 6 conductors/ slot. If its
driven at 500 rpm calculate the induced emf. Assume coil span as 150 electrical and flux per pole 40mwb. (6)
2. Constructional features of cylindrical rotor alternator.
3. a. Explain the construction of salient pole Synchronous machine. (10)
b. From the following test result, determine the volt. Reg. of a 2000v, 10 alternator delivering a I2 = 100 A at 0.8 pf lagging. (6)
Test results: An excitation of 2.5A produces a current of 100a in the stator winding on Short Circuit & an emf of 500v in open circuit. Assume an effective resistance of 0.8 ohm.
4. Explain the principle of operation of hysteresis motor.(8)
5. Explain the principle of operation of reluctance machine. (8)
6. Explain the principle of operation of synchronous motor. (8)
UNIT-V
1. Describe with neat diagram the constructional features of DC machines.
2. Derive the expression for generated emf in a DC machine.(8)
3. Discuss the characteristics of DC motors.
4. Derive the torque equation of a DC motor from first principle.(8)
5. What do you mean by losses method & briefly explain it.
6. Discuss in detail the methods of control of speed of a DC motor.