DieselShip's Online Content Library

Q4. A. (i) Discuss the various hazards and problems which are associated with electric cable Insulation in the event of fire.

(ii) Suggest remedies for these problems.

B. State how the spread of fire may be reduced by the method used for installing electric cables.

Q3. Differentiate between squirrel cage and wound rotor motor of the three phases: a.c. induction. In respect of the following; A. Rotor construction, B. Torque characteristic, C. Speed variation.

Q3. Diesel electric propulsion is now being chosen as the power plant for an increasingly wide variety of vessels.

(a) Sketch a simple layout of such an installation.

(b) Explain the advantages of selecting such a plant.

Q4. In the event of a failure, of the main electrical power supply on a: ship, an emergency source of power must be available, state the circuits which must be fed from such a source and discuss the reasons governing the selection of such circuits.

Q5. With reference to the condition monitoring of electrical machinery:

A. State TWO important parameters that may be recorded;

B. Explain how the parameters are measured and what defects may be revealed.

Q6. (a). Explain the significance of the root- mean- square value of an alternating current or voltage waveform; Define the form factor of such a wave form.

(b). A total load of 8000 kW at 0.8 power factor is supplied by two alternators in parallel. One alternator supplies 6000 kW at 0.9 power factor. Find the kVA rating of the other alternator and the power factor.

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. A. List the factors that determine the starting torque of the three-phase induction motor. How does this torque generally compare with the value of the rated torque?

B. The low-voltage release of an a.c. motor-starter consists of a solenoid into which an iron plunger is drawn against a spring. The resistance of the solenoid is 35 ohm. When connected to a 220 V, 50 Hz, a.c. supply the current taken is at first 2A, and when the plunger is drawn into the “full-in” position the current falls to 0.7 A. Calculate the inductance of the solenoid for both positions of the plunger, and the maximum value of flux-linkages in weber-turns for the “full-in” position of the plunger.

Q6. A. With the aid of delta and star connection diagrams, state the basic equation from which   delta – star – delta conversion equation can be derived.

B. Three batteries A, B and C have their negative terminals connected together, between the positive terminals of A and B there is a resistor of 0.5 ohm and between B and C three is a resistor of 0.3 ohm,

i. Battery A 105 V, Internal resistance 0.25 ohm’

ii. Battery B 100 V, Internal resistance 0.2 ohm

iii. Battery C 95 V, Internal resistance 0.25 ohm

Determine the current values in the two resistors and the power dissipated by them.