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Q7. a) State the conditions, which must be satisfied before an A.C generator can be paralleled with live bus-bars. (4)

b) Sketch a lamp-bright configuration for synchronizing lamps. (8)

c) State the advantages and disadvantages of the lamps-bright system over lamps-darks system. (4)

Q3. (a) Sketch, the circuit diagram of an instrument used for measuring electrical insulation resistance. (8)

(b) Describe the circuit diagram sketched in (a), explaining how it operates when measuring electrical insulation resistance. (8)

Q1. a) Explain the working principle of an alkaline battery. (8)

b) Compare the alkaline battery with Lead-Acid battery. (8)

Q4. a) What is the purpose of AVR in an alternator? (6)

b) With the aid of a simple circuit diagram explain the basic working of a brushless alternator. (10)

Q7. In the following circuit, E1 = 13 V, E2 = 19.5 V, R1 = 5 W, R2 = 7 W, R3 = 9 W. Find the current flowing through each resistor. (16)

Q7. A 24V emergency battery is to be charged from the 110V ship's mains when the e.m.f. per cell has fallen to a minimum value of 1.8V. The battery consists of 12 cells in series, has a capacity of 100 Ahr at a 10 hr rate and the internal resistance is 0.03Ω/cell. If charging continues until the voltage per cell rises to 2.2V, find the value of the variable resistor needed to control the charging. The charging current can be assumed to be equal to the maximum allowable discharge current (16)

Q9. A wooden ring having a mean diameter of 200 mm and a cross-sectional area of 400 mm2 is wound uniformly with a coil of 300 turns. If the current passed through the coil is 5 A calculate the value of flux produced in the coil. (16)

Q6. A coil of resistance 10 ohm and inductance 0.1H is connected in series with a capacitor of capacitance 150pF, across a 200 V, 50 Hz supply.

Calculate:

a) the inductive reactance. (3)

b) the capacitive reactance. (3)

c) the circuit impedance. (2)

d) the circuit current. (2)

e) the circuit power factor. (2)

f) the voltage drop across the coil. (2)

g) the voltage drop across the capacitor. (2)

Q1. (a) Sketch a diesel electric propulsion arrangement for a ship (8)

(b) Describe the operation of the propulsion arrangement sketched in (a), including in your description how reversal of the propulsion motor is achieved (8)

Q2. Differentiate between squirrel cage and wound rotor motors, of the three phase a.c. induction type, in respect of the following: (16)

(a) Rotor construction

(b) Torque characteristics

(c) Speed variation

Q3. (a) Explain open loop control system and closed loop control system with suitable examples (8)

(b) What are the merits and demerits of the two systems? (8)

Q4. (a) Explain why it is necessary to have reverse power protection for alternators intended for parallel operation (6)

(b) (i) Sketch a reverse power trip (5)

(ii) Explain briefly the principle on which the operation of this power trip is based and how tripping is activated (5)

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

(a) State TWO important parameters that may be recorded (8)

(b) Explain how the parameters are measured and what defects may be revealed (8)

Q6. (a) Describe the basic principles of a self-excited generator (6)

(b) The armature resistance of a 200 V, shunt motor is 0.4 ohms and the no-load armature current is 2A. When fully loaded and taking an armature current of 50 A, the speed is 1200 rev/min. Find the no-load speed and state the assumption made in the calculation (10)

Q7. A 4 pole, lap wound shunt generator delivers 200 A at terminal voltage of 250 V. It has a field and armature resistance of 50 Ω and 0.05 Ω respectively. Determine: (16)

(a) Armature current

(b) Generated e.m.f

(c) Current per armature parallel paths

(d) Power developed

Q8. (a) State the relationship between impedance, voltage and current (6)

(b) The filament of a 230V lamp takes a current of 0.261A when working at its normal temperature of 2000° C. The temperature coefficient of the tungsten filament material can be taken as 0.005 ohms/ohms at 0ºC/ºC. Find the approximate current which flows at the instant of switching on the supply to the cold lamp, which can be considered to be at a room temperature of 20° C (10)

Q9. (a) Describe the effect of running an induction motor on reduced voltage (6)

(b) A 90V D.C. generator is used to charge a battery of 40 cells in series, each cell having an average e.m.f. of 1.9 V and an internal resistance of 0.0025 Ω. If the total resistance of the connecting cells is 1Ω, calculate the value of the charging current (10)