DieselShip's Online Content Library

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)

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.

Q8. A. Explain the significance of the root mean square value of an alternating current or voltage wave form; Define the form factor of such a wave form.

B. Two 10 MVA 3 phase Alternator operate in parallel to supply at 0.8 power factor with lagging load of 15 MVA. If the output of one Alternator is 8 MVA at 0.9 lagging.

1. Calculate the output of second Alternator.

2. Calculate the value of Power factor of second Alternator.

Q5. Fig Q3 shows a single stage transistor amplifier. The voltage between base and emitter is 0.3 V and the d.c. voltage at the output terminals is 8 V. (a) Calculate EACH of the following, assuming the base current is small enough to be neglected: (i) The voltage between emitter and collector; (ii) The power developed in the 150Ωresistor; (iii) The power dissipated in the transistor. (b) Sketch the circuit diagram and show the additional components needed to make the amplifier suitable for amplifying small a.c. signals.

Q10. the following loads are supplied by two alternators running in parallel 1. 1400kw@pf 0.86 lagging 2. 900 kw @ pf 0.8 lagging. 3. 800 kw @ pf unity 4 500kw @pf0.8 leading. If the load on one machine is adjusted to 2100kw @ pf of 0.92 find the load and p.f of the other machine.

Q7. A. Distinguish between power efficiency and all-day efficiency. Why is all-day efficiency considered more reasonable basis for comparison than ordinary efficiency? B. The no-load current of a transformer is 5.0 Amps, power factor 0.25 when supplied at 235 V, 50 Hz. Turns on the primary winding is 200. Calculate A. the maximum value of flux in the core, B. the core loss.

Q9. (a) Explain the concept of dynamical stability.

(b) A ship of 5000 tonne displacement has three rectangular double bottom tanks A: 12m long and 16m wide; Tank B: 14m long and 15m wide; C 14m long and 16m wide.

calculate the free surface effect for any one tank and state in which order the tanks should be filled when making use of them for stability correction.

Q10. A ship of 15000 tonne displacement has an Admiralty Coefficient, based on shaft power, of 420. The mechanical efficiency of the machinery is 83%, shaft losses 6%, propeller efficiency 65% and QPC 0.71. At a particular speed the thrust power is 2550kW.

Calculate:

(i) Indicated power,

(ii) Effective power,

 (iii) Ship speed.

Q10. With reference to the wake of a vessel:

a. Explain Wake fraction and Quasi Propulsive co-efficient(QPC).

b. A ship travelling at 15.5 knots has a propeller of 5.5 m pitch turning at 95 rev/min. The thrust of the propeller is 380 KN and the delivered power 3540 KW. If the real slip is 20% and the thrust deduction factor O.198, calculate the Quasi Propulsive Coefficient (QPC) and the wake fraction.