Download EX-503put - Corporate Group of Institutes

CORPORATE INSTITUTE OF SCIENCE AND TECHNOLOGY
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGG
IMP QUESTIONS FOR PUT (Nov 2015)
ELECTRICAL MACHINES –II (EX-503)
UNIT-I
Q.1 . What is armature reaction in D.C. machines ? How it can be reduced.
Q.2. Explain the construction of a D.C. machine with a neat diagrame.
Q.3. Compare the Lap and wave windings ?
Q.4.What is commutation ? What are the methods of improving commutation?
Q.5.What is the function of commutator in a D.C. machine?
Q.6 .classify the D.C. machines with diagrams .
Q.7.Derive the EMF equation of a D.C. generator .
Q.8.Describe the working of following :
(a) Metadyne (b) Amplidyne (c) PMDC motor (d) Brush less D.C. motor.
Q. 9 A D.C. generator has an armature emf of 100V when the useful flux per pole is 20mWB and the
speed is 800rpm calculate the generated emf (a) with same flux and a speed of 1000 rpm. (b) with a
flux per pole of 24 m wb and a speed of 900 rpm .
Q.10. An 8-pole generator has 500 armature conductors and has a useful flux per pole of 0.065Wb .
What will be the emf generated if it is lap connected and runs at 1000 rpm ? What must be the
speed at which it is to be driven to produce the same emf if it is wave connected ?
Q.11 Draw all the performance characteristics of a d.c. shunt generator?
UNIT-II
Q. 1 Explain the working principle of a D.C. motor ?
Q.2 What is back EMF in D.C. motor ?
Q.3 What is the necessity of starter in D.C. motor ?
Q.4. Describe the following tests of D.C. motor:
(a) Swinburn’s test (b) Hopkinson’s Test
Q.5 Describe the working of following :
(a) Three point starter (b) Four point starter
Q.6 What are the methods of speed control of a D.C. motor describe them in brief .
Q.7 Why the Swinburn’s test can not be performed on D.C. series motor .
Q.8 Define following with reference to D.C. shunt motor :
(a) Critical speed (b) Critical resistance
Q.9 A four pole 250V ,wave connected shunt motor gives 10KW when running at 1000rpm and
drawing armature and field currents of 60A and 1A respectively . It has 560 conductors. Its armature
resistance is 0.2 ohm. Assuming a drop of 1V per brush ,determine (a) Total torque (b) useful torque
(c) flux per pole (d) rotational iosses (e) efficiency .
Q.10.A 250 V D.C. shunt motor having an armature resistance of 0.25 ohm carries an armature
current of 50A and runs at 750 rpm .If the flux is reduced by 10%, find the speed . Assume that the
load torque remains constant .
UNIT-III
Q.1. What are the different types of excitation systems for a Synchronous machine.
Q.2 . What are the advantages of distributed and short pitched winding?
Q.3 Define following : (a) Distribution factor (b) Pitch factor
Q.4. Draw the phasor diagrame of a synchronous generator by clearly indicating V, Ef ,δ . Ff ,Fa, Fr .
Q.5. Write the step by step procedure to determine the voltage regulation by MMF method ?
Q.6. Write the step by step procedure to determine the voltage regulation by ZPF (potier ) method ?
Q.7. The stator of a three phase ,16-pole alternator has 144 slots and there are 4 conductors per slot
connected in two layers and the conductors of each phase are connected in series. If the speed of
the alternator is 375 rpm. Calculate: EMF induced per phase . The resultant flux in the air gap is
0.05Wb per pole . Assume the coil span as 150 electrical degree.
Q.8 A 3-phase ,1500KVA, star –connected,50Hz, 2300V alternator has a resistance between each
pair of terminals as measured by direct current is 0.16 ohm.Assume that the effective resistance is
1.5 times the ohmic resistance. A field current of 70A produces a short-circuit current equal to full
load current of 376A in each line.The same field current produces an emf of 700V on open circuit.
Determine the synchronous reactance of the machine and its full regulation at 0.8 power factor
lagging.
Q.9. Explain how the armature reaction depends on power factor in a synchronous generator .
Q.10. Derive the formula for distribution factor and pitch factor.
UNIT-IV
Q.1. Explain two reaction theory of salient pole synchronous machine.
Q.2. What is SCR (Short circuit Ratio) of synchronous machine ? what is its significance.
Q.3.What are the conditions for parallel operation of alternators?
Q.4 . Define the synchronizing power ?
Q.5. Define the synchronizing torque ?
Q.6. The speed regulations of two 800 KW alternators A and B running in parallel are 100% to 104%
and 100% to 105% from full load to no load respectively. How will the two alternators share a load of
1000KW ?
Q.7. Describe the bright lamp method with circuit diagram to synchronize the two alternators .
Q.8 Give the circuit diagram to determine Xd and Xq in lab by slip test.
Q.9 Explain the power angle characteristics of synchronous machine.
UNIT-V
Q.1 . Explain the principle of operation of synchronous motor .
Q.2. How the synchronous motor is made self starting.
Q.3. Explain the phenomena of hunting in synchronous machine? What are its effects and how it can
be minimised .
Q.4. Explain V-curves and inverted V-curves of synchronous motor .
Q.5. Define the following : (a) Running torque (b) Pull-in torque (c) pull-out torque (d) locked-rotor
torque
Q.6 Write short note on any two of following: (a) Reluctance motor (b) Hysteresis motor (c)
Repulsion motor (d) Stepper motor .
Q.7. How the synchronous motor works as power factor correction device .