DieselShip's Online Content Library

Q1. A. Sketch a circuit diagram of a push button direct online contactor starter for a three phase Incorporating overload and short circuit protection.

B. Indicate, on a sketch of the typical characteristic curves of current and torque against Speed, disadvantages of a direct on line start squirrel cage induction motor.

Q2. Tank liquid level sensors are an integral part of ships. Describe with aid of suitable sketches the working principle of,

(a) capacitive type level sensor;

(b) Ultrasonic level sensor;

(c) Float.

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

A. Rectifier circuit;

B. Amplifier circuit;

C. Oscillator circuit.

Q4. A. Describe with the aid of a simple sketch the arrangement of the three-phase winding of an alternator showing the neutral point.

B. Explain why for most ships the neutral point is insulated.

C. Explain why in some installation the neutral point is earthed?

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;

Q6. A. Describe the normal criteria used for setting thermal protection relays and its advantage compared to magnetic types.

B.  An 18.65 kW,4-pole,50HZ, 3 phase induction motor has friction and windage losses of 2.5 percent of the output. The full load slip is 4% compute for full load (a) the rotor Cu loss (b) the rotor input (c) the shaft torque (d) the gross electromagnetic torque.

Q7. With reference to adjoining circuit calculate following. (a) Current in each branch of circuit. (b) Total current.

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.

Q9. A 20kVA, 2000/220V, single-phase transformer has a primary resistance of 2.1Ω and a secondary resistance of 0.026Ω. The corresponding leakage reactance’s are 2.5Ω and 0.03Ω. Estimate the regulation at full load under power-factor conditions of.

(a) Unity;

(b) 0.5 (lagging) and

(c) 0.5 (leading).

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.