** **

**NOTE: There are 9 Questions in
all.**

·
**Question
1 is compulsory and carries 20 marks. Answer to Q. 1. must be written in the
space provided for it in the answer book supplied and nowhere else.**

·
**Out of
the remaining EIGHT Questions answer any FIVE Questions. Each question carries
16 marks.**

·
**Any
required data not explicitly given, may be suitably assumed and stated.**

** **

** **

**Q.1 Choose
the correct or best alternative in the following: (2x10)**

** **

a. The eddy current loss in an a-c electric motor is 100 watts at 50 Hz. Its loss at 100 Hz will be

** (A)** 25 watts** (B)
**59 watts

**(C)**
100 watts** (D) **400 watts

b. The maximum power for a given excitation in a synchronous motor is developed when the power angle is equal to

** (A)** _{}** (B)
**_{}

**(C)** _{}** (D)
**_{}

c. A commutator in a d.c. machine

**(A)
**Reduces
power loss in armature.

**(B)
**Reduces
power loss in field circuit.

**(C)
**converts
the induced a-c armature voltage into direct voltage.

**(D)
**Is not
necessary.

d. The speed of a d.c. shunt motor at no-load is

**(A)
** 5 to
10% **(B)** 15 to 20%

**(C)** 25 to 30% **(D)**
35 to 40%

higher than its speed at rated load.

e. The efficiency of a transformer is mainly dependent on

**(A)** core losses. **(B)**
copper losses.

**(C)** stray losses. **(D)**
dielectric losses.

f. When two transformers are operating in parallel, they will share the load as under:

**(A)
**proportional
to their impedances.

**(B)
**inversely
proportional to their impedances.

**(C)
**50% -
50%

**(D)
**25%-75%

g. If the voltage is reduced to half, the torque developed by an induction motor will be reduced to

**(A)
**_{} of original
torque. **(B)** _{} of original torque.

**(C) **_{} of original torque. **(D)**
_{} of
original torque.

h. A 3-phase, 400 votts, 50 Hz, 100 KW, 4 pole squirrel cage induction motor with a rated slip of 2% will have a rotor speed of

**(A)
**1500
rpm **(B)** 1470 rpm

**(C) **1530 rpm **(D)
**1570 rpm

** **

i. If the phase
angle of the voltage coil of a directional relay is _{}, the maximum torque angle
of the relay is

**(A)
**** **_{} **(B)**
_{}

**(C) **_{} **(D)
**_{}

j. The voltage at the two ends of a transmission line are 132 KV and its reactance is 40 ohm. The Capacity of the line is

**(A) **435.6 MW **(B)**
217.8 MW

**(C)** 251.5 MW **(D)
**500 MW

**Answer any FIVE Questions out of EIGHT
Questions. **

**Each question carries 16 marks.**

**Q.2** A
50 KVA, 2300/230 V, 60 Hz transformer has a high voltage winding resistance of
0.65 _{} and
a low-voltage winding resistance of 0.0065 _{}. Laboratory tests showed the
following results:

Open circuit test: V = 230 V, I =5.7A, P = 190 W

Short circuit test: V=41.5 V, I=21.7 A, P=No watt meter was used.

a. Compute
the value of primary voltage needed to give rated secondary voltage when the
transformer is connected as a step-up one and is delivening 50 KVA at a power
factor of 0.8 lagging. **(12)**

b. Compute
the efficiency under conditions of part (a). **(4)**

**Q.3** A
three-phase, 335-hp, 2000V, six pole, 60 Hz, Y-connected squirrel-cage
induction motor has the following parameters per phase that are applicable at
normal slips:

_{}

_{}

_{}

The rotational losses are 4100 watts. Using the approximate equivalent circuit, compute for a slip of 1.5%.

(i) the line power factor and current.

(ii) developed torque.

(iii)
efficiency. **(8+4+4)**

** **

**Q.4** A
2300-V, three phase, 60 Hz, star-connected cylindrical synchronous motor has a
synchronous reactance of 11 _{} per phase. When it delivers 200 hp,
the efficiency is found to be 90% exclusive of field loss, and the power-angle
is 15 electrical degrees as measured by a stroboscope. Neglect ohmic resistance
and determine:

(i) the induced excitation per phase.

(ii)
the line
current _{}

(iii)
the power
factor **(8+4+4)**

**Q.5** When a 250-V, 50
hp, 1000 rpm d.c shunt motor is used to supply rated output power to a constant
torque load, it draws an armature current of 160A. the armature circuit has a
resistance of 0.04 _{} and the rotational losses are equal
to 2 KW. An external resistance of 0.5 _{} is inserted in series with the
armature winding. For this condition compute

(i) the speed

(ii) the developed power

(iii)
the efficiency assuming that the field loss is
1.6 K.W **(8+4+4)**

** **

** Q.6 **Give the lay-out of a typical thermal-power plant and briefly
explain the working of the super heater and the condenser. **(8+4+4)**

**Q.7** With
a neat diagram describe the construction of a lead acid cell and explain the
process of charging and discharging of the cell. **(8+4+4)**

**Q.8** a. What
are the criteria for the classification of transmission lines as short, medium
and long lines? **(8)**

** **

b. Draw
the schematic diagram of a directional overcurrent relay and explain its
working. **(4)**

** **

** **c. What are the advantages
of high voltage transmission and its limitations. **(4)**

**Q.9** Write
short notes on **ANY TWO** of the following:

** **

(i) Capacitor-start motor.

(ii) Switched reluctance motor.

(iii)
Stepper
motor. **(8+8)**