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Q1. State essential electrical services on board that are able to be operable under fire conditions.

b) Explain how electric cables for the essential services in part (a) pass through bulkheads whilst maintaining gas tight and water tight integrity.

c) State the requirements for the cables which supply electrically driven emergency fire pumps.

Q2. a) Sketch a basic circuit showing a d.c, winch motor driven by a Ward Leonard circuit powered by a single speed squirrel cage motor.

b) Explain how reversal of the winch motor is achieved using the Ward Leonard system

c ) State advantage and disadvantage of the Ward Leonard drive system.

Q3. Compare methods of obtaining speed regulation of three-phase induction motor generally used in tankers by means of:

A. Rotor resistance; B. Cascade system; C. Pole-changing.

Give examples where each system may be employed with advantage.

Q4.a) State the primary function of an AVR.

(b) State conditions external to a generator that cause its terminal voltage to drop.

(c) Sketch a clearly labelled, typical AVR response curve, identifying the application of load recovery time, maximum acceptable voltage dip, and the permissible steady-state voltage regulation.

(d) State the function of an AVR trimming potentiometer for each of the following cases

(i) when a generator operates in standalone mode

(ii) when a generator operates in parallel.

Q1. A. Sketch a circuit diagram of a push button direct online contactor starter for a three phase Incorporating overload and short circuit protection.

B. Indicate, on a sketch of the typical characteristic curves of current and torque against Speed, disadvantages of a direct on line start squirrel cage induction motor.

Q5. A. Differentiate between series and parallel resonances. Draw impedance characteristics of these circuits. B. A 2,000-K VA, 3-phase, 8-pole alternator runs at 750 r.p.m in parallel with other machines on 6,000 V bus-bars. Find synchronizing power on full-load 0.8 p.f. lagging per mechanical degree of displacement and the corresponding synchronizing torque. The synchronous reactance is 6 ohms per phase.

Q9. A. Discuss different methods of speed control of a d.c. series motor by adjusting field ampere turns.

B. A 230 V, d.c. shunt motor runs at 1000 r.p.m and takes 5 amperes. The armature resistance of the motor is 0.025𝛀 and shunt field resistance is 230𝛀. Calculate the drop in speed when the motor is loaded and takes the line current of 41 amperes. Neglect armature reaction.

Q9. A. What are the factors which determine the synchronous speed of a motor? B. The star-connected rotor of an induction motor has a stand-still reactance of 4.5 ohms/phase and a resistance of 0.5 /phase. The motor has an induced emf of 50 V between the slip-rings at stand-still on open circuit when connected to its normal supply voltage. Find the current in each phase and the power factor at start when the slip-ring is short-circuited.

Q8. A. Explain the purpose of interlopes and state their magnetic polarity relative to the main poles of both generators and motors.

A 200V, long-shunt compound-wound generator has a full-load output of 20kW. The various resistances are as follows; armature (including brush contact) 0.15 ohm, series field 0.025 ohm, interpole field 0.028 ohm, shunt field (including the field-regulator resistance) 115 ohm. The iron losses at full load are 780W, and the friction and wind age losses 590W. Calculate the efficiency at full load.

Q10. What is direct-connected alternator? How is a direct-connected exciter arranged in an alternator?  Sketch a graph of starting current, and torque against the speed of rotation for a single cage motor. A 440V shunt motor takes an armature current of 30A at 700 rev/min. The armature resistance is 0.7 ohm. If the flux is suddenly reduced 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.