MET-Feb-2021

Q1. With reference to the provision of a shore electrical supply to a ship:

A. Sketch an arrangement for taking A.C. shore supply and checks to be carried out prior Taking shore connection?

B. Describe the method of safely connecting the arrangement sketched in (A) to the shore Supply?

Q2. With respect to the High Voltage power systems installation, explain the different types of circuit breaker that are used, comparing them on merits and de-merits. Describe the theory of arc phenomenon and the mechanism fitted to mitigate the arc.

Q3. A. Describe with the aid of a simple sketch the arrangement of the three phase winding of an alternator showing the neutral point; 

B. Explain why for most ships the neutral point is insulated; 

C. Explain why in some installation the neutral point is Earthed.

Q4. What is the meant by "excitation" in an alternator? With the help of a neat diagram of brushless alternator labeling all the important parts. explain how the excitation is achieved in a brushless alternator.

Q5. What is a soft starting of an Induction motor? Describe with a circuit using a thyristors used for soft starting. Discuss its advantages and dis-advantages.

Q6. A. Explain the potential hazards of liquid-cooled transformers are used onboard ships.

B. What are the losses in transformers? Mention the various factors which affect these losses.

In a 25 KVA, 3300/233 V, single phase transformer, the iron and full-load Cu. Losses are respectively 350 and 400 watts. Calculate the efficiency at half-full load, 0.8 power factor.
 

Q7. A. Describe how protection against short circuit is provided in a 3 phase induction motor circuit.

B. Explain how rotating magnetic field is produced in three phase winding with three phase supply.

A 4-pole, 3-phase induction motor operates from a supply whose frequency is 50 Hz. Calculate
(i) Speed at which the magnetic field of the stator is rotating,
(ii) speed of the rotor when the slip is 0.04,
(iii) the frequency of the rotor current when the slip is 0.03.

Q8. 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.

 

Q9. A. Explain the effect of making incorrect phase and starter connections.

B. A 440V shunt motor tenets an armature current of 30A at 700 rev/min. The armature resistance is 0.7ohm. If the flux is suddenly reduced by 20 per cent, to what value will the armature current rise momentarily? Assuming unchanged resisting torque to motion, what will be the new steady values of speed and armature current? Sketch graphs showing armature current and speed as functions of time during the transition from initial to final, steady-state conditions.
 

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?