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Posted Date: 14 Aug 2009 Posted By: ananth Member Level: Gold

2009 Jawaharlal Nehru Technological University Electrical and Electronics Engineering Code No: 35010 Set No.4 III B.Tech I Semester Supplimentary Examinations, May/Jun 2009 ELECTRICAL MACHINES-III (Electrical & Electronic Engineering) Question paper

Course: B.Tech Electrical and Electronics Engineering

University: Jawaharlal Nehru Technological University

Code No: 35010 Set No. 4
III B.Tech I Semester Supplimentary Examinations, May/Jun 2009
ELECTRICAL MACHINES-III
(Electrical & Electronic Engineering)
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
? ? ? ? ?
1. (a) Explain the various winding factors? Explain the effects of each of them.
(b) Determine the slot distribution and the pole phase group sequence for a 45
slot, 6 pole, 3- winding. [6+10]
2. (a) Explain the operation and effect of load power factor on the performance of
alternator.
(b) The effective resistance of a 2200 V, 50 Hz, 440 kVA, single phase alternator is
0.5
. On short circuit, a field current of 4 A gives the full load current. The
EMF on open circuit for the same field current is 1160 V. Find Synchronous
impedance, Synchronous reactance and % regulation of 0.6p.f lagging. [8+8]
3. (a) Explain the various tests to be conducted on an alternator to find the voltage
regulation of an alternator.
(b) Explain the effect of ‘Saturation’ on the performance of an alternator. How
the effect of saturation can be overcome in calculation. [8+8]
4. (a) Explain all the necessary conditions for successful parallel operation of alter-
nators.
(b) A 2 MVA, 3-, star connected, 4 pole, 750 RPM alternator is operating on
6000 V bus bars, xs is 6
/ph. Find synchronizing power and torque for full
load 0.8 power factor lagging. [8+8]
5. A 3- , 30 kW, 400 V, star connected synchronous motor operates on full load at 0.8
pf lagging. The machine has synchronous reactance of 4
& negligible armature
resistance. Calculate the new value of current & power factor if the excitation is
increased by 50%. [16]
6. The data for no load saturation curve of a 6.6 kV, 1.8 MVA. 3-, 50 Hz, star con-
nected synchronous motor is given below:
V (k V) 3.6 5.9 7.4 7.9 8.4
If Amp 45 91 130 160 210
The effective resistance & synchronous reactance per phase of the motor are 0.35

& 7
respectively. Plot the V curves for this machine when the input is maintained
constant at 450 kW. [16]
7. (a) Explain, the speed of single phase Induction motor can be controlled by
supply voltage where as them is not possible with 3 - IM, why?(b) The name plate of single phase IM, 4 pole Induction motor gives the following
data:
Output = 410 W, Supply voltage = 230 V, Frequency = 50 Hz,
Input current = 3.2 A, Power factor = 0.7, speed = 1410 RPM.
Calculate:
i. The efficiency of the motor
ii. The slip of the motor when delivering rated output. [8+8]
8. Write short notes on following:
(a) AC series motor
(b) Universal motor
(c) Variable reluctance stepper motor
(d) Permanent magnet stepper motor.

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