DieselShip's Online Content Library

Q1. Sketch and describe the method of speed control of synchronous motors by variable frequency. State the advantages of this method over the other methods of speed control.

Q1. What is a marine high voltage system? Sketch and describe a shipboard high voltage switch board and its protective devices.

Q2. What is soft starting of an Induction motor? Describe with a circuit using thyristors used for soft starting. Discuss its advantages and dis-advantages.

Q1. A. Sketch a main engine shaft driven generator arrangement with an electronic system for frequency correction.  B. Describe the operation of the generator arrangement sketched in (A).

Q4. With reference to preferential tripping in a marine electrical distribution system.

A. With the aid of a sketch, describe a typical arrangement to provide three stages of tripping an instantaneous protection against short circuit.

B. State why this protection is required;

Q7. A. By means of a schematic circuit diagram illustrate the peak rectifier. If the supply voltage is v(t) = Vm Sin wt, what is the voltage across the load resistor?

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.

Q8. A. Why is it important to maintain high efficiency of operation?  And low values of voltages regulation for power transformers?

B. A 100 KVA transformer has 400 turns on the primary and 80 turns on the secondary. The primary and secondary resistances are 0.3 and 0.01 respectively, and the corresponding leakage reactance’s are 1.1 and 0.035 respectively. The supply voltage is 2200 V. Calculate:

(i) The equivalent impedance referred to the primary circuit;

(ii) The voltage regulation and secondary terminal voltage for full load having a power factor of (i) 0.8 lagging and (ii) 0.8 leading.

Q9. Explain What is meant by, and the significance of, four of the following terms.

I. Voltage Stabilization,

II. Filter choke;

III. Impedance,

IV. Rectification,

V. Grid bias voltage.

Q7. A. Which of the following three motors has the poorest speed regulation: shunt motor, series Motor or cumulative compound motor? Explain.

B. A 440V shunt motor takes an armature current of 30A at 700 rev/min. The armature resistance is 0.7ohm. If the flux is suddenly reduced by 20 per cent, to what value will the armature current rise momentarily? Assuming unchanged resisting torque to motion, what will be the new steady values of speed and armature current? Sketch graphs showing armature current and speed as functions of time during the transition from initial to final, steady-state conditions.