DieselShip's Online Content Library

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. Sketch a circuit diagram of an emergency generator power supply system suitable for passenger vessel: including in yours diagram the essential services supplied. With reference to an emergency generator stage - Its location; Methods of automatic starting; The time available for starting and connection of power to switchboard; Angles of heel and trim up to which it must be capable of operating; The length of time it must be cable of supplying emergency power

Q4. Explain the effect of reduced voltage on standard squirrel cage motors with respect to EACH of the following:

(i) Burn out; (ii) Starting current; (iii) Starting torque; (iv) Speed.

Q1. Differentiate with the aid of simple sketches between the following types of electronic circuits;

A. Rectifier circuit;

B. Amplifier circuit;

C. Oscillator circuit.

Q2. With reference to U.M.S. operations:

A. State with reasons the essential requirements for unattended machinery spaces;

B. As second Engineer, describe how you would respond to the irretrievable failure of the Machinery space fire alarm system whilst the ship is on voyage.

Q6. A. Describe with the aid of a sketch, an isolator for a 3 phase 440V, 20-amp electric supply List the safety features of the isolator described in the sketch. B. A moving coil ammeter, a thermal ammeter and a rectifier are connected in series with a resistor across a 110 V sinusoidal a.c. supply. The circuit has a resistance of 50 to current in one direction and, due to the rectifier, an infinite resistance to current in the reverse direction. Calculate: (i) The readings on the ammeters; (ii) The form and peak factors of the current wave.

Q7. A. What is leakage flux as it applies to the iron-core transformer? How is it taken into account in the analysis of the transformer?

B. The following results were obtained on a 50KVA transformer: open circuit test-primary voltage, 3300V; secondary voltage, 415 V; primary power, 430 W. Short circuit test primary voltage, 124V; primary current, 15.3 A; primary power, 525 W; secondary current full load value. Calculate: (i) The efficiencies at full load and at half load for 0.7 power factor (ii) The Voltage regulations for power factor 0.7 (i) Lagging, (ii) leading (iii) The secondary terminal voltages corresponding to (i) and (ii)

Q8. A. What is silicon controlled rectifier (SCR)? How is the break over voltage of the SCR defined?  B. A d.c. motor takes an armature current of 110 A at 480 V. The resistance of the armature circuit is 0.2 . The machine has six poles and the armature is lap-connected with 864 conductors. The flux per pole is 0.05 Wb. Calculate - (i) The speed; (ii) The gross torque developed by the armature

Q9. A. Show how the power that is transferred across the air gap of the three-phase induction motor is represented. Explain the terms. What portion of this is useful power? B. The primary and secondary windings of a 500 Kva transformer have resistance of 0.42 and 0.0019 respectively. The primary and secondary voltages are 11 000 V and 415 V respectively and the core loss is 2.9 Kw, assuming the power factor of the load to be 0.8. Calculate the efficiency on (i) Full load; (ii) Half load;

Q10. A 100 Kw, 460 V shunt generator was run as a motor on no load at its rated voltage and speed. The total current taken was 9.8 A, including a shunt current of 2.7 A. The resistance of the armature circuit at normal working temperature was 0.11  Calculate the efficiencies at i. Full load; ii. Half load