DieselShip's Online Content Library

Q1. (a) Sketch a diesel electric propulsion arrangement for a ship (8)

(b) Describe the operation of the propulsion arrangement sketched in (a), including in your description how reversal of the propulsion motor is achieved (8)

Q2. Differentiate between squirrel cage and wound rotor motors, of the three phase a.c. induction type, in respect of the following: (16)

(a) Rotor construction

(b) Torque characteristics

(c) Speed variation

Q3. (a) Explain open loop control system and closed loop control system with suitable examples (8)

(b) What are the merits and demerits of the two systems? (8)

Q4. (a) Explain why it is necessary to have reverse power protection for alternators intended for parallel operation (6)

(b) (i) Sketch a reverse power trip (5)

(ii) Explain briefly the principle on which the operation of this power trip is based and how tripping is activated (5)

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

(a) State TWO important parameters that may be recorded (8)

(b) Explain how the parameters are measured and what defects may be revealed (8)

Q6. (a) Describe the basic principles of a self-excited generator (6)

(b) The armature resistance of a 200 V, shunt motor is 0.4 ohms and the no-load armature current is 2A. When fully loaded and taking an armature current of 50 A, the speed is 1200 rev/min. Find the no-load speed and state the assumption made in the calculation (10)

Q7. A 4 pole, lap wound shunt generator delivers 200 A at terminal voltage of 250 V. It has a field and armature resistance of 50 Ω and 0.05 Ω respectively. Determine: (16)

(a) Armature current

(b) Generated e.m.f

(c) Current per armature parallel paths

(d) Power developed

Q8. (a) State the relationship between impedance, voltage and current (6)

(b) The filament of a 230V lamp takes a current of 0.261A when working at its normal temperature of 2000° C. The temperature coefficient of the tungsten filament material can be taken as 0.005 ohms/ohms at 0ºC/ºC. Find the approximate current which flows at the instant of switching on the supply to the cold lamp, which can be considered to be at a room temperature of 20° C (10)

Q9. (a) Describe the effect of running an induction motor on reduced voltage (6)

(b) A 90V D.C. generator is used to charge a battery of 40 cells in series, each cell having an average e.m.f. of 1.9 V and an internal resistance of 0.0025 Ω. If the total resistance of the connecting cells is 1Ω, calculate the value of the charging current (10)