AMIETE – ET (OLD SCHEME)

Code: AE10 Subject: ELECTRICAL ENGINEERING

Time: 3 Hours Max. Marks: 100

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 the best alternative in the following: (210)

a. Copper losses at full load operation are 1600 W. If the load on the transformer is

reduced to 75% of full load, the copper losses will be

(A) 1600 W (B) 1200 W

(C) 900 W (D) 800 W

b. At the instant of starting, the per unit slip of the 3-phase induction motor is

(A) 0.05 (B) 0.1

(C) 1.0 (D) 0.5

c. The commutator of dc motor serves the purpose of

(A) Changing ac into dc (B) Converting dc into ac

(C) Reducing friction (D) Avoiding arc at the brushes

d. In an ordinary transformer which of the following does not change

(A) Voltage (B) Current

(C) Frequency (D) All of the above

e. A 220 V dc shunt motor develops a torque of 54 Nm at an armature current of 10 A. The torque developed for the armature current of 20 A is

(A) 54 Nm (B) 81 Nm

(C) 108 Nm (D) None of the above

f. For a 3-phase 4 pole 50 Hz synchronous motor, the frequency, no. of poles and the load torque are all halved. The motor speed will be

(A) 375 rpm (B) 75 rpm

(C) 1500 rpm (D) 3000 rpm

g. While starting a synchronous motor its field winding should be kept

(A) Short circuit (B) Open

(C) Connected to dc source (D) None of these

h. A wound rotor induction motor can be distinguished from squirrel cage

induction motor by

(A) Presence of slip-rings (B) Size of frame

(C) Shaft diameter (D) None of these

i. Control rods used in nuclear reactor made of

(A) Zirconium (B) Boron

(C) Beryllium (D) Lead

j. In comparison with diesel power plant the gas turbine power plant has

(A) Lower overall thermal efficiency (B) Higher overall thermal efficiency

(C) Same overall thermal efficiency (D) Unpredictable

Answer any FIVE Questions out of EIGHT Questions.

Each question carries 16 marks.

Q.2 a. Draw an approximate equivalent circuit of a transformer. Based upon it derive the expression for its regulation. (8)

b. The efficiency of a 400 kVA single phase transformer is 98.77% when delivering full load at 0.8 p.f. and 99.13% at half load and unity p.f. Calculate (i) iron losses and (ii) full load copper losses. (8)

Q.3 a. Explain with suitable diagram the construction details of a salient pole alternator. (8)

b. A 2800 V, 3-phase, star connected motor has a synchronous reactance of 5π per phase. The motor input is 1000 kW at rated voltage and an excitation emf of 3600 V (line). Calculate the line current and power factor. (8)

Q.4 a. Draw and explain load characteristics curve for various types of dc generator. (8)

b. A 200 V dc series motor runs at 500 rpm when taking a current of 25 A. The resistance of the armature is 0.5 W and that of field is 0.3 W. If the current remains constant, calculate the resistance necessary to reduce the speed to 250 rpm. (8)

Q.5 a. Explain with the help of a diagram how a rotating magnetic field is produced in the air gap of 3-phase induction motor. (8)

b. Write short notes on

(i) Torque-speed characteristics of 3-phase induction motor.

(ii) Application of 1-phase induction motors. (8)

Q.6 a. Explain the construction and working principle of a universal motor and mention its applications. (8)

b. Describe the construction of hysteresis motor and show that it develops a running torque both at synchronous and asynchronous speed of the rotor. (8)

Q.7 a. Draw neat sketch of a thermal electric power plant station and explain the function of major components in it. (8)

b. What is wind energy? How can wind energy be converted into electric energy? (8)

Q.8 a. Design precisely the ‘Voltage Regulation’ of a transmission line and discuss qualitatively its dependence on the load power factor. Can the regulation be negative? If so, under what conditions? (8)

b. What do you understand by carrier current protection? Explain. (8)

Q.9 a. What are the advantages of electric heating? Give classification of various electric heating methods along with brief account of their working principles. (8)

b. Write short technical notes on any TWO of the following:

(i) Lead Acid cell.

(ii) Nickel Cadmium cell.

(iii) Button cell. (4 2)