DieselShip's Online Content Library

Q3. A. Sketch a standby battery charging/discharging circuit;

B. Describe the circuit sketched, making special reference to how battery charge is maintained and how it operates upon loss of main power.

Q3. A. Explain why it is necessary to have reverse power protection for alternators intended for operation.

B.(i) Sketch a reverse power trip; (ii) Explain briefly the principle on which the operation of this power trip is based and how tripping is activated.

Q2. A. (i) Describe with the aid of a sketch the operation of a synchro scope; (ii) State the information obtained from it. B. Suggest a substitute in the event of synchro scope and stand by light failure.

Q3. List at least two factors that cause deterioration of the frequency response of a transistor amplifier. Explain how each factor affects the performance of the amplifier and the portion of the frequency range where it is effective. (16)

Q4. Differentiate with the aid of simple sketches between two of the following types of electronic circuits.

A. Rectifier circuit (6)

B. Amplifier circuit (5)

C. Oscillator circuit (5)

Q6. A. What are the characteristics of PN junction diode? Point out its specifications. Also point out the significance of dynamic and static resistances.

B. Draw the circuit of Half-wave rectifier and its output waveform. A diode whose internal resistance is 20 is to supply power to 1000 load from 110 V (RMS) source. Calculate

(i) peak load current, (ii) DC load current, (iii) AC load current.

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. 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.

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.

Q10. A. Why is a synchronous motor not self-starting? What are the various ways in which it can be started?

B. A 500V, single phase synchronous motor gives a net output mechanical power of 7.46kW and operates at 0.9 power factor lagging. Its effective resistance is 0.8 . If the iron and friction losses are 500 w and excitation losses are 800w, calculate the armature current and the commercial efficiency.