Code No: 310205

III B-Tech I-Semester Regular Examinations

November - 2003
Set No: 4

ELECTROMECHANICS - III

(Electrical and Electronics Engineering)

[Time:3 hours]
Max. Marks: 80

Answer any FIVE questions

ALL questions carry equal marks

1. Draw a winding diagram for 3-phase, 2layer, lap winding with two slots per pole per phase what are the modifications to be made in the diagram if it is wave winding.

2. Write short notes on the following:

a) Armature reaction and leakage reactance.
b) Phasor diagram of an alternator loaded.

3. A 600KVA, 3300V, 8-pole, 3-phase, 50Hz alternator has the following characteristics

Amp-turns/pole   4000   5000   7000  10000       

Terminal EMF     2850   3400    3850   4000

There are 200 conductors in series per phase. Find the SC characteristics, the field ampereturns for full load 0.8 P.f (Lagging)and the voltage regulation, having given that the inductive drop at full load is 7% and that the equivalent armature reaction in amp-turns per pole =1.06X ampere-conductor per phase per pole

4. Two similar 6000V, 3-phase generators are running in parallel at frequency bus bars. Each has an equivalent resistance and reactance of 0.05 ohms and 0.5ohms respectively and supplies one half of a total load of 10000KW at a lagging power factor of 0.8 the two machines being similarly excited if the excitation of one machine is adjusted until the armature current is 438 A and the steam supply to the turbine remains unchanged, find the armature current, the emf and the power factor of the other alternator.

5. A synchronous motor has an equivalent armature reactance of 3.3 Ω. The exciting current is adjusted to such a value that the open circuit emf is 950V. Find the pf at which the motor would operate when it takes 80KW from 800V supply line.

6. a) Explain the operation of a synchronous motor with variable load at constant excitation.

b) Derive the torque developed in a synchronous motor.

7. a) Draw the equivalent circuit of a single phase induction motor and discuss the experimental procedure to determine the parameters

b) Find the mechanical power out put of a 185Watts, 4pole 110volts,5 0Hz single phase induction motor whose constant are given below at a slip of 0.05

R1=1.86 ohms        x1=2.56 ohms
xm=53.5 ohms         R2=3.56 ohms
x2=2.56 ohms       Core loss=4.0 Watts
Friction and windage losses=13.0 Watts

8. a) Discuss the difference between capacitor start induction run motor and capacitor start and run induction motor. Draw the performance characteristics.

b) The following tests results were obtained in respect of 230Volts single phase induction motor

No load tests 230V, 6.25A 360Watts
locked rotor test 126v,15.0A. 577Watts
stator winding resistance = 1.5 ohms
Draw the equivalent circuit diagram with parameters