MET-JAN-2020

Q1. What are semiconductor devices? What are its advantages over thermionic devices? With respect to semi-conductor devices describe working principle and application of the following A. Zener Diode B. Transistor, C. Photocell, D. Thyristor
 

Q2. Tank liquid level sensors are an integral part of ships. Describe with aid of suitable sketches the working principle of,
(a) capacitive type level sensor;
(b) Ultrasonic level sensor;
(c) Float.

Q3. The direct on line start of squirrel cage motor is used for most electrical drives on a.c. powered ships.
Describe with sketches as necessary one method of overcoming each of the following Problems:
A. High starting current; B. Low starting torque.

Q4. A. (i) Discuss the various hazards and problems which are associated with electric cable Insulation in the event of fire.
(ii) Suggest remedies for these problems.
B. State how the spread of fire may be reduced by the method used for installing electric cables.

Q5. A. What are the causes of overheating of an induction motor?
B. What preventive measures are provided against damage to an induction motor in installed condition?
C. What is the purpose of ‘fuse back up protection’ provided to an induction motor?
D. How does an induction motor develop torque?
E. What is the condition to be satisfied for achieving maximum running torque in an induction motor?

Q6. A. Explain the significance of the root mean square value of an alternating current or voltage wave form; Define the form factor of such a wave form.

B. A total load of 8000 kW at 0.8 power factor is supplied by two alternators in parallel. One alternator supplies 6000 kW at 0.9 power factor. Find the KVA rating of the other alternator and the power factor.

 

 

Q7. A. By means of a schematic circuit diagram illustrate the peak rectifier. If the supply voltage is v(t) = Vm Sinωt, what is the voltage across the load resistor?

B. A battery-charging circuit is shown below in Fig. The forward resistance of the diode can be considered negligible and the reverse resistance infinite. The internal resistance of the battery is negligible. Calculate the necessary value of the variable resistance R so that the battery charging current

is 1.0 A.

 

Q8. A. What is back emf? Derive the relation for the back emf and the supplied voltage in terms of armature resistance.

B. A three phase induction motor is wound for four poles and is supplied from a 50 Hz system. Calculate.
i. The synchronous speed;
ii. The speed of the rotor when the slip is 4 per cent;
iii. The motor frequency when the speed of the rotor is 600 r.p.m

 

Q9. A. What are the factors which determine the synchronous speed of a motor?

B. Three conductors fitted side by side in the stator of a salient-pole alternator. Each generates maximum voltage of 200V (sinusoidal). The angle subtended at the centre of the stator between adjacent conductors is 20 electrical degrees. If the three conductors are connected in series, find
(i) the r.m.s. value of the effective voltage and
(ii) the ‘breadth factor’. Using the theory that is the basis of this problem, give one reason why three-phase current has been introduced.

 

Q10. A. Compare the effectiveness of a current limiting circuit breaker with that of a HRC fuse.

B. A coil having a resistance of 10 Ohm, and an inductance of 0.15 H is connected in series with a capacitor across a 100V, 50Hz supply. If the current and the voltage are in phase what will be the value of the current in the circuit and the voltage drop across the coil?