DieselShip's Online Content Library

Q6. (a) What is the metric length of one shackle of an anchor chain? (4)

(b) A vessel of 10000 t displacement burns 25 t of fuel per day when her speed is 12 knots. Calculate the probable consumption of fuel over a voyage of 3000 nautical miles at a speed of 11 knots with a displacement of 11000t. (12)

Q6. (a) The capacitor-start induction run motor has a much higher starting torque than the resistance split-phase motor. Explain (6)

(b) A 100 KVA, 2400/240 V, 50 Hz, 1-phase transformer has no- load current of 0.64 A and a core loss of 700 W, when its high voltage side is energized at rated voltage and frequency. calculate the two components of no-load current. If this transformer supplies a load current of 40 amp at 0.8 lagging power factor at its low voltage side, determine the primary current and its power factor. Ignore leakage impedance drop. (10)

Q6. (a) Why is it important to maintain high efficiency of operation and low values of voltages regulation for power transformers? (6)
(b) A 20 KVA, 2000/220V, single-phase transformer has a primary resistance of 2.1 Ω and a secondary resistance of 0.026 Ω, The corresponding leakage reactance’s are 2.5 Ω and 0.03 Ω. Estimate the regulation at full load under power-factor conditions of;
(i)  unity

(ii) 0.5 (lagging)

(iii) 0.5 (Leading) (10)

Q5. A shunt generator has an induced emf of 254 V. When the generator is loaded, the terminal voltage is 240 V, Neglecting armature reaction, find the load current if the armature resistance is 0.04 ohm and the field circuit resistance is 24 ohms. (16)

Q6. A 3000 KVA, 6-pole 3 phase, star connected alternator runs at 1000 r.p.m. in parallel with other machines on 3300V bus-bars. The synchronous reactance is 25%. Calculate the synchronizing power for one mechanical degree of displacement and the corresponding synchronizing torque. (16)

Q8. A. With reference to an A.C. generator used in marine practice derive an expression for the frequency of the generated e.m.f. in terms of the speed of the machine and the number of poles. (6)

B. 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 windage losses 590W. Calculate the efficiency at full load. (10)

Q8. A. What is a commutator? Discuss its rectifying action in detail.

B. Calculate the e.m.f. generated by a 4-pole, wave wound armature having 40 slots with 18 conductors per slot when driven at 1000 r.p.m. The flux per pole is 0.015 wb.

Q10.  (a). Describe the no-load saturation characteristic of a d.c. generator.

(b). A 4-pole machine running at 1500 r.p.m. has an armature with 80 slots and 6 conductors per pole. The flux per pole is 6 x 106 lines. Determine the terminal e.m.f. of d.c. generator if the coils are lap connected. If the current per conductor is 100 A, determine the electrical power.

Q8. A. Electric motors contain a stationary member as well as a rotating member. For each of the following machines, identify in which part of the motor three field winding and the armature winding are located: three phase induction motor, three phase synchronous motor, d.c. motor. B.  An 18.65 KW,4-pole,50HZ, 3 phase induction motor has friction and windage losses of 2.5 percent of the output. The full load slip is 4% compute for full load (a) the rotor Cu loss (b) the rotor input (c) the shaft torque (d) the gross electromagnetic torque.

Q8. A current has the following steady values in amperes for equal intervals of time and changing instantaneously from one value to next: - 0,10,20,30,20,10,0,0, -10,-20,-30,-20,-10,0 etc. Calculate I. Average value 2. RMS value, 3. Form factor and peak factor.

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.

Q10. A ship of length 140m, Breadth of 18.5m, draught of 8.1m and a displacement of 17,025 tonnes in sea water, has a face pitch ratio of 0.673. Diameter of the Propeller is 4.8m. The results of the speed trial show that true slip may be regarded as constant over a range of 9 to 13 knots and is 30%, w = 0.5CB-0.05. If fuel used is 20t/day at 13 knots and fuel consumption/day varies as cube of speed of ship, Determine the fuel consumption, when propeller runs at 110 rpm.