DieselShip's Online Content Library

Q6. a) What are the various resistances acting against the motion of the ship? (6)

b) A vessel uses 300 t of fuel on a voyage of 3000 nautical miles at a speed of 12 knots when her displacement is 10000 t. Estimate the fuel required for an estimated voyage of 1500 nautical miles at a speed of 15 knots and displacement of 14000 t. (10)

Q9. a) Name the various types of capacitors? (6)

b) A 500W, 100V bulb is to be connected across 250V, 50Hz mains. Find the value of the capacitor required to be connected in series. (10)

Q7. Ten thousand cubic millimeters of copper are

a) Drawn into a wire 100 metres long,

b) Rolled into a square sheet of 100 mm side. Find the resistance of the wire and the resistance between opposite faces of the plate, if the resistance of the copper is 17 μΩmm or 1.7 x 10-8 ohms-metres. (16)

Q9. a) Differentiate between resistance, induction and impedance in an a.c. circuit. (6)

b) A circuit is made up from resistors of value 2Ω, 4Ω, 5Ω and 10Ω connected in parallel. If the current is 8.6A, find the voltage drop across the arrangement and the current in each resistor. (10)

Q6.a) What is the effect on the field flux of an alternator current in the synchronous motor that leads the terminal voltage. (6)

b) A 1,000-kVA, 11,000-V, 3-ϕ, star-connected synchronous motor has an armature resistance and reactance per phase of 3.5 Ω and 40 Ω respectively. Determine the induced e.m.f. and angular retardation of the rotor when fully loaded at (a) unity p.f. (b) 0.8 p.f. lagging (c) 0.8 p.f. leading. (10)

Q8. (a) Compare fixed pitch with controllable pitch propellers. (6)

(b) A ship of 12400 tonne displacement is 120 m long, 17.5 m beam and floats at a draught of 7.5 m. The propeller has a pitch ratio of 0.75 and, when turning at 100 rev/min, produces a ship speed of 12 knots with a real slip of 30%. Calculate the apparent slip, pitch and diameter of the propeller. The wake fraction w may be found from the expression. w = 0.5Cb - 0.05 (10)

Q4. With respect to circuit breakers:

a) Compare the effectiveness of a current limiting circuit breaker with that of a HRC fuse. (6)

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 100 V, 50 Hz 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? (10)

Q5. A) By means of a schematic circuit diagram illustrate the peak rectifier. If the supply voltage is v(t) = Vm Sinwt, what is the voltage across the load resistor? (6)

b) A battery-charging circuit is shown below in fig. The forward resistance of the diode can be considered negligible and the reverse resistance infinite. The internal resistance of the battery is negligible. Calculate the necessary value of the variable resistance R so that the battery charging current is 1.0 A. (10)

Q4.a) Explain the construction and principle of operation of permanent magnet moving coil instrument. (8)

b) A permanent magnet moving coil instrument has a coil of dimension 15 mm × 12mm. The flux density in the air gap is 1.8 × 10-3 wb/m2 and the spring constant is 0.4 × 10-6 Nm / rad. Determine the number of turns required to produce an angular deflection of 900 when a current of 5 mA is flowing through the coil. (8)

Q4. a) A 440 V, 10KW 0.8 pf phase load is supplied as shown.

Calculate short circuit fault current at the load and at the main switch board (8)

b) Explain the safe working procedure that you will follow while working in live MSB bus bar. (8)

Q7. (a) Compare constant current method and constant voltage method of charging batteries. (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 /ºC at 0°C. 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)

Q7. A. Discuss different methods of speed control of a d.c. series motor by adjusting field ampere turns. (6)

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. (10)