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Q2. A. State the necessary conditions required prior to the synchronizing of electrical alternators.

B. Describe the type of cumulative damage that may be caused when alternators are incorrectly synchronized;

C. Explain how the damage referred to in (b) can be avoided / reduced.

D. For two alternators operating in parallel state the consequences of:

(i) Reduced torque from the prime mover of one machine.

(ii)Reduced excitation on one machine.

Q4. In the event of a failure, of the main electrical power supply on a: ship, an emergency source of power must be available, state the circuits which must be fed from such a source and discuss the reasons governing the selection of such circuits.

Q1. With reference to squirrel cage, induction, electric motors:

A. Describe the construction of such a motor.

B. Sketch the torque against speed curve of such a motor;

C. Describe a method employed by a retrofitted device used to improve the part load

performance of an induction motor.

Q4. With reference to a 3 speed a.c. cage motor driven cargo winch:

A. Sketch a circuit diagram for a pole change motor;

B. Describe how speed change and braking are achieved.

Q5. With reference to the condition monitoring of electrical machinery:

A. State TWO important parameters that may be recorded;

B. Explain how the parameters are measured and what defects may be revealed.

Q6. A. A series circuit having resistance, Inductance and capacitance is to be operated on a constant voltage supply of available frequency. Indicate graphically how changes will take place in the terms, Reactive terms, i.e. Capacitive reactance and inductance reactance; B. A resistance of 130 ? and a capacitor of 30µF are connected in parallel across a 230 Volt, 50Hz supply. Find the current in each component, total current, phase angle and the power consumed.

Q9. A. Explain the working principal of a 3-phase induction motor. What are the various types of rotors? B. An 18.65Kw, 6-pole, 50Hz, 3 phase slip ring induction motor runs at 960 rpm on full load with a rotor current per phase of 35A, allowing 1Kw for mechanical losses, find the resistance per phase of 3-phase rotor winding.

Q8. A. (i) What is direct-connected alternator? (3)

(ii)  How is a direct-connected exciter arranged in an alternator? (3)

B. A twelve-pole, three-phase, delta-connected alternator runs at 600 rev/min and supplies a balanced star-connected load. Each phase of the load is a coil of resistance 35 ohm and inductive reactance 25 ohm. The line terminal voltage of the alternator is 440V. Determine (a) frequency of supply, (b) current in each coil, (c) current in each phase of the alternator, (d) total power supplied to the load. (10)

Q9. Sketch a graph of starting current, and torque against the speed of rotation for a single cage motor.  B. A 230V motor, which normally develops 10Kw at 1000 rev/min with an efficiency of 85%, is to be used as a generator. The armature resistance is 0.15Ohm and the shunt field resistance is 220Ohm. If it is driven at 1080 rev/min and the field current is adjusted to 1.1A by means of the shunt regulator what output in Kw could be expected as a generator, if the armature copper loss was kept down to that when running as a motor.

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?