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Q1. A. Sketch a main engine shaft driven generator arrangement with an electronic system for frequency correction.  B. Describe the operation of the generator arrangement sketched in (A).

Q2. With reference to testing High Voltage equipment:

(a) Explain why earthing down is considered essential.

(b) Briefly describe the procedures of earthing down

(c) describe how an insulation resistance test is carried out on High Voltage equipment, making reference to personnel safety;

(d) Describe, with the aid of a sketch, a method to detect earth leakage in EACH of the following systems:

(i) Earthed

(ii) Insulated

Q9. Explain What is meant by, and the significance of, four of the following terms.

I. Voltage Stabilization,

II. Filter choke;

III. Impedance,

IV. Rectification,

V. Grid bias voltage.

Q4. Explain the meaning of ‘P’ and ‘N’ types semi-conductor materials and give a brief description of the mechanism by which current passes through them.

Q5. With reference to electronic control systems A. Draw a simple block diagram for temperature control B. Describe each component shown in the diagram in (a).

Q6. a) Derive the expression for current and voltage relations between line and phase values in the star and delta cases. Draw vector diagram.

b) Three impedances Z=5+j4 are connected in the form of a delta to the three loads of a balanced 3-phase circuit. The line voltage is 120 Volts.

Find (a) The phase current, (b) Power factor, (c) The volt-ampere in the circuit.

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.