Marine Engineering Technology

Direct on line starting for large induction motors such as those for bow thruster units, may not be viable.

(a) State the reasons for this. (4)

(b) Sketch a starting system that may be used for such motors. (8)

(c) Describe the starting method sketched in Q. 1(b) (4)

(a) Sketch a basic circuit showing a d.c., winch motor driven by a Ward Leonard circuit powered by a single speed squirrel cage motor. (8)

(b) Explain how reversal of the winch motor is achieved using the Ward Leonard system. (4)

(c) State advantage and disadvantage of the Ward Leonard drive system. (4)

(a) Draw a circuit diagram of a transistor connected as a common emitter amplifier including bias resistors, coupling and decoupling capacitors. (10)

(b) Explain the operation of the circuit components. (6)

(a) Describe a brush less alternator with a.c. exciter and static A.V.R. (8)

(b) State the output voltage characteristics for this type of machine. (8)

(a) Explain the purpose of a rectifier and the effect of over current and of overvoltage on rectifiers. (6)

(b) Three equal resistors are connected to a three-phase system, If one resistor is removed find the reduction in load if they are connected in (i) Star, (ii) Delta. (10)

(a) What are the characteristics of PN junction diode? Point out its specifications. Also point out the significance of dynamic and static resistances. (6)

(b) Draw the circuit of Half-wave rectifier and its output waveform. A diode whose internal resistance is 20 Ω is to supply power to 1000 Ω load from 110 V (RMS) source. Calculate (i) peak load current, (ii) DC load current, (iii) AC load current. (10)

(a) Describe the no-load saturation characteristic of a d.c. generator. (6)

(b) Find the synchronous impedance and reactance of an alternator in which a given field current produces an armature current of 200 A on short-circuit and a generated e.m.f. of 50 V on open- circuit. The armature resistance is 0.1 ohm. To what induced voltage must the alternator be excited if it is to deliver a load of 100 A at a p.f. of 0.8 lagging, with a terminal voltage of 200 V. (10)

(a) What is a commutator? Discuss its rectifying action in detail. (6)

(b) Calculate the e.m.f. generated by a 4-pole, wave wound armature having 40 slots with 18 conductors per slot when driven at 1000 r.p.m. The flux per pole is 0.015 wb. (10)

(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? (6)

(b) A 440 V load of 400 kW at 0.8 (lagging) power factor is jointly supplied by two alternators A and B. The kW load on A is 150 kW and the kVAr load on B is 150 kVAr (lagging). Determine the kW load on B, the kVAr load on A, the power factor of operation on each machine and the current loading of each machine. (10)

(a) Why is a synchronous motor not self-starting? What are the various ways in which it can be started? (6)

(b) A 500 V, single phase synchronous motor gives a net output mechanical power of 7.46 kW and operates at 0.9 power factor lagging. Its effective resistance is 0.8 Ω. If the iron and friction losses are 500 W and excitation losses are 800 W, calculate the armature current and the commercial efficiency. (10)

(a) What is intrinsic electric safety? (6)

(b) Can live maintenance be done on intrinsically safe circuits? (5)

(c) Describe intrinsically safe equipment used on board ship. (5)

With reference to testing High Voltage equipment:

(a) Explain why earthing down is considered essential (3)

(b) Briefly describe the procedures of earthing down (3)

(c) Describe how an insulation resistance test is carried out on High Voltage equipment, making reference to personnel safety. (4)

(d) Describe, with the aid of a sketch, a method to detect earth leakage in EACH of the following systems: (6)

(i) earthed

(ii) insulated

Explain what is meant by, and the significance of, four of the following terms: (16)

(a) Voltage stabilization

(b) Filter choke

(c) Impedance

(d) Rectification

(e) Grid bias voltage

Explain the meaning of "p" and "n" type semi-conductor materials and give a brief description of the mechanism by which current passes through them. (16)

With reference to electronic control systems:

(a) Draw a simple block diagram for temperature control. (8)

(b) Describe each component shown in the diagram in (a). (8)

(a) Derive the expression for current and voltage relations between line and phase values in the star and delta cases. Draw vector diagram. (6)

(b) A balanced delta connected load is connected to a 415V, 50 Hz supply. If the per phase impedance of the load is (8+ j12) ohm, calculate: (10)

(i) the phase current of the load.

(ii) line current

(iii) power consumed by each phase.

(a) Discuss different methods of speed control of a d.c. series motor by adjusting field ampere turns. (6)

(b) A 230 V, d.c. shunt motor runs at 1000 r.p.m. and takes 5 amperes. The armature resistance of the motor is 0.025 Ω and shunt field resistance is 230 Ω. Calculate the drop in speed when the motor is loaded and takes the line current of 41 amperes. Neglect armature reaction. (10)

(a) What are the factors which determine the synchronous speed of a motor? (6)

(b) The star-connected rotor of an induction motor has a stand-still reactance of 4.5 Ω/phase and a resistance of 0.5 Ω/phase. The motor has an induced emf of 50 V between the slip-rings at stand-still on open circuit when connected to its normal supply voltage. Find the current in each phase and the power factor at start when the slip-rings are short-circuited. (10)

(a) Explain the purpose of interpoles and state their magnetic polarity relative to the main poles of both generators and motors. (6)

(b) A 200V, long-shunt compound-wound generator has a full-load output of 20kW. The various resistances are as follows; armature (including brush contact) 0.15 ohm, series field 0.025ohm, interpole field 0.028ohm, shunt field (including the field-regulator resistance) 115ohm. The iron losses at full load are 780W, and the friction and windage losses 590W. Calculate the efficiency at full load. (10)

(a) (i) What is direct-connected alternator? (3)

(ii) How is a direct-connected exciter arranged in an alternator? (3)

(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 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. (10)

(a) Sketch a main engine shaft driven generator arrangement with an electronic system for frequency correction. (8)

(b) Describe the operation of the generator arrangement sketched in (a). (8)

With reference to electronic control systems:

(a) Draw a simple block diagram for temperature control. (8)

(b) Describe each component shown in the diagram in (a). (8)

(a) Sketch a circuit diagram for an automatic voltage regulator illustrating how the A.V.R. utilizes a Silicon-controlled rectifier to control the excitation system for an alternator. (8)

(b) Describe how the A.V.R. monitors output and controls the excitation system. (8)

It is proposed to operate a Bow thruster unit from a 3.3 KV electrical supply.

Outline suitable options for the design of installation under each of the following heading. (16)

(a) Protection of the main switch board

(b) Overload of bow thruster motor

(c) Cable protection.

With reference to a three-phase shipboard electrical distribution system: (16)

(a) Enumerate the advantages of an insulated neutral system.

(b) Enumerate the disadvantages of an insulated neutral system.

(c) Describe how the earthed neutral system is Earthed.

(d) Compare the use of an insulated neutral system as opposed to the use of an Earthed neutral system with regard to the risk of electric shock from either system.

(a) A series circuit having resistance, Inductance and capacitance is to be operated on a constant voltage supply of available frequency. Indicate graphically how changes will take place in the resistive terms, reactive terms, i.e. capacitive reactance and inductive reactance. (6)

(b) A resistance of 130 Ω and a capacitor of 30µF are connected in parallel across a 230 Volt, 50Hz supply. Find the current in each component, total current, phase angle and the power consumed. (10)

(a) Explain the working principle of a three-phase induction motor. What are the various types of rotors? (6)

(b) An 18.65kW, 6-pole, 50Hz, 3 phase slip ring induction motor runs at 960 rpm on full load with a rotor current per phase of 35A, allowing 1kW for mechanical losses, find the resistance per phase of 3-phase rotor winding. (10)

(a) Explain why the iron losses in a transformer are substantially independent of the load current. (6)

(b) The equivalent circuit for a 200/400-V step-up transformer has the following parameters referred to the low-voltage side. (10)

Equivalent resistance = 0.15 Ω: Equivalent reactance = 0.37 Ω

Core-loss component resistance = 600 Ω: Magnetising reactance = 300 Ω

When the transformer is supplying a load at 10 A at a power factor if 0.8 lag, Calculate:

(i) the primary current.

(ii) secondary terminal voltage.

(a) Sketch a graph of starting current, and torque against the speed of rotation for a single cage motor. (6)

(b) A 230 V motor, which normally develops 10kW at 1000 rev/min with an efficiency of 85%, is to be used as a generator. The armature resistance is 0.15 Ohm and the shunt field resistance is 220 Ohm. If it is driven at 1080 rev/min and the field current is adjusted to 1.1A by means of the shunt regulator what output in kW could be expected as a generator, if the armature copper loss was kept down to that when running as a motor. (10)

(a) Compare the effectiveness of a current limiting circuit breaker with that of a HRC fuse. (6)

(b) A coil having a resistance of 10 Ohm, and an inductance of 0.15 H is connected in series with a capacitor across a 100 V, 50 Hz supply. If the current and the voltage are in phase what will be the value of the current in the circuit and the voltage drop across the coil? (10)

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

(a) Rotor construction

(b) Torque characteristic

(c) Speed variation.

With reference to an emergency source of electrical power in cargo ships: (16)

(a) Describe a typical power source.

(b) Give a typical list of essential services, which must be supplied simultaneously.

(c) Explain how the emergency installation can be periodically tested.

The direct online start of squirrel cage motor is used for most electrical drives on A.C. powered ships. Describe with sketches as necessary one method of overcoming each of the following Problems:

(a) High starting current. (8)

(b) Low starting torque. (8)

(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. (8)

(b) State how the spread of fire may be reduced by the method used for installing electric cables. (8)

(a) What are the causes of overheating of an induction motor? (4)

(b) What preventive measures are provided against damage to an induction motor in installed condition? (3)

(c) What is the purpose of 'fuse back up protection' provided to an induction motor? (3)

(d) How does an induction motor develop torque? (3)

(e) What is the condition to be satisfied for achieving maximum running torque in an induction motor? (3)

(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. (6)

(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. (10)

(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? (6)

(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. (10)

(a) Why is it important to maintain high efficiency of operation and low values of voltage regulation for power transformers? (6)

(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 Ω and 0.01 Ω respectively and the corresponding leakage reactances are 1.1 Ω and 0.035 Ω respectively. The supply voltage is 2200 V. Calculate: (10)

(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 (a) 0.8 lagging and (b) 0.8 leading.

(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? (6)

(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 ohms. When connected to a 220 V, 50 Hz, A.C. supply the current taken is at first 2 A, 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. (10)

(a) With the aid of delta and star connection diagrams, state the basic equation from which the delta-star and star-delta conversion equation can be derived. (6)

(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 there is a resistor of 0.3 ohm.

Specifications of the three batteries are given below: (10)

Battery A 105 V, Internal resistance 0.25 ohm

Battery B 100 V, Internal resistance 0.2 ohm

Battery C 95 V, Internal resistance 0.25 ohm

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

With reference to a three-phase shipboard electrical distribution system:

(a) Enumerate the advantages of an insulated neutral system. (4)

(b) Enumerate the disadvantages of an insulated neutral system. (4)

(c) Describe how the Earthed neutral system is Earthed. (4)

(d) Compare the use of an insulated neutral system as opposed to the use of an Earthed neutral system with regard to the risk of electric shock from either system. (4)

(a) Explain the meaning of the term power factor correction. (4)

(b) State TWO advantages of power factor correction. (4)

(c) Explain, with the aid of a circuit diagram, how power factor correction can be effected in a three phase circuit using capacitors. (4)

(d) Explain ONE method other than the use of capacitors by means of which power factor correction may be effected. (4)

List at least two factors that cause a deterioration of the frequency response of a transistor amplifier. Explain how each factor affects the performance of the amplifier and the portion of the frequency range where it is effective. (16)

(a) Explain what is meant by the term single phasing. (5)

(b) Explain the probable effect of single phasing on a delta connected squirrel cage induction motor on 75% full load. (5)

(c) State a method by which a motor can be protected against the effects of single phasing. (6)

(a) Describe the circuit breaker for an a.c. generator using a sketch to show how arcing controlled. (6)

(b) Explain the sequence of events that might occur if the breaker opens on a short circuit and state the check you would require following such event. (5)

(c) Give a safe procedure to follow should a main circuit breaker fail to open under fault condition. (5)

(a) Explain what is meant by the terms wave form, frequency and average value. (6)

(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 Ω to current in one direction and, due to the rectifier, an infinite resistance to current in the reverse direction. Calculate: (10)

(i) the readings on the ammeters.

(ii) the form and peak factors of the current wave.

(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? (6)

(b) The following results were obtained on a 50 kVA transformer: open circuit test-primary voltage, 3300 V; 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: (10)

(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).

(a) What is a silicon controlled rectifier (SCR)? How is the breakover voltage of the SCR defined? (6)

(b) A d.c. motor takes an armature current of 110 A at 480 V. The resistance of the armature circuit is 0.2 Ω. The machine has six poles and the armature is lap-connected with 864 conductors. The flux per pole is 0.05 Wb. Calculate: (10)

(i) The speed;

(ii) The gross torque developed by the armature.

(a) List the factors that determine the maximum developed torque of the induction motor. (6)

(b) The primary and secondary windings of a 500 kVA transformer have resistances of 0.42 and 0.0019 respectively. The primary and secondary voltages are 11000 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: (10)

(i) Full load.

(ii) Half load;

A balanced star connected three phase load has a coil of inductance 0.2 H and resistance 50 Ω in each phase. It is supplied at 415 V, 50 Hz. Calculate EACH of the following: (16)

(a) the line current;

(b) the power factor;

(c) the value of each of three identical delta connected capacitors to be connected across the same supply to raise the power factor to 0.9 lag;

(d) the new value of the line current.

(a) Describe the circuit breaker for an a.c. generator using a sketch to show how arcing is Controlled.

(b) Explain the sequence of events that might occur if the breaker opens on a short circuit and state the check you would require following such event

(c) Give a safe procedure to follow should a main circuit breaker fail to open under fault Condition.

(a) With respect to measuring instruments what is the difference between analogue and digital measuring instruments. Explain the working principle of each type.

(b) Describe with the aid of simple sketches one analogue and one digital measuring instrument you have used onboard.

With respect to power transformers kindly explain the following protections

(a) Overload protection

(b) Overcurrent protection for phase faults

(c) Earth Fault protection

(d) Differential protection

(e) Directional protection

In a.c. generators, voltage dip occurs in two stages.

(a) (i) Sketch a voltage-time graph showing the pattern of voltage dip.

(ii) Referring to this graph, state with reasons the effect on the electrical system of a small power installation when a large load is suddenly switched

(b) Explain EACH of the following categories of voltage control:

(i) Error operated;

(ii) Functional.

In some circumstances electrical current may be induced into the shafting of rotating machinery.

(a) state the problem that may be caused by this current.

(b) explain with the aid of sketches, how currents may be avoided or reduced in the following instances:

(i) d.c. machines

(ii) main shafting fitted with a bronze propeller.

(a) Explain the significance of the root mean square value of an alternating current or voltage wave form; Define the form factor of such a wave form (6)

(b) Draw the circuit of Half-wave rectifier and its output waveform. A diode whose internal resistance is 20 Ω is to supply power to 1000 Ω load from 110 V (RMS) source. Calculate (10)

(i) peak load current,

(ii) DC load current,

(iii) AC load current

(a) By means of a schematic circuit diagram illustrate the peak rectifier. If the supply voltage is v(t) = Vra Sin wt, what is the voltage across the load resistor? (6)

(b) A d.c. motor takes an armature current of 110 A at 480 V. The resistance of the armature circuit is 0.2Ω. The machine has six poles, and the armature is lap-connected with 864 conductors. The flux per pole is 0.05 Wb. Calculate: (10)

(i) The speed;

(ii) The gross torque developed by the armature

(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? (6)

(b) A three-phase induction motor is wound for four poles and is supplied from a 50 Hz system. Calculate: (10)

(i) The synchronous speed.

(ii) The speed of the rotor when the slip is 4 per cent.

(iii) The rotor frequency when the speed of the rotor is 600 r/min.

(a) What is leakage flux as it applies to the iron-core transformer? How is it considered in the analysis of the transformer? (6)

(b) Three conductors fitted side by side in the stator of a salient-pole alternator. Each generates a maximum voltage of 200V (sinusoidal). The angle subtended at the centre of the stator between adjacent conductors is 20 electrical degrees. If the three conductors are connected in series, find:

(i) the r.m.s. value of the effective voltage and

(ii) the 'breadth factor'. Using the theory that is the basis of this problem, give one reason why three-phase current has been introduced. (10)

(a) What are the factors which determine the synchronous speed of a motor? (6)

(b) A twelve-pole, three-phase, delta connected alternator runs at 600 rev/min and supplies a balanced star connected load. Each phase of the load is a coil of resistance 35 ohm and inductive reactance 25 ohm. The line terminal voltage of the alternator is 440V. Determine (10)

(i) frequency of supply,

(ii) current in each coil,

(iii) current in each phase of the alternator,

(iv) total power supplied to the load.

(a) List the various losses which occur in a squirrel cage induction motor on load.

(b) State which of these losses is:

(i) Independent of load current and speed;

(ii) dependent on load current;

(iii) dependent on speed.

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.

(a) Draw a circuit diagram illustrating how a single thyristor ('silicon controlled rectifier') may be used to provide a variable voltage d.c. output from a single phase a.c. supply.

(b) Explain how the firing angle of the thyristor is varied.

(c) Sketch waveforms for the output voltage when the firing angle is:

(i) 60°;

(ii) 120°.

With reference to a 3 speed A.C. motor driven cargo winch:

(a) Sketch a circuit diagram for a pole change motor;

(b) Describe how speed change and braking are achieved.

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.

(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. (6)

(b) A total load of 8000 kW at 0.8 power factor is supplied by two alternators in parallel. One alternator supplies 6000kW at 0.9 power factor. Find the KVA rating of the other alternator and the power factor. (10)

(a) By means of a schematic circuit diagram illustrate the peak rectifier, if the supply voltage is v(t) = V Sin wt, what is the voltage across the load resistor? (6)

(b) A series circuit comprising a 50Ω resistor, a coil having resistance and inductance and a capacitor is connected across a 50 V variable frequency supply. When the frequency is 400 Hz the current reaches its maximum value of 0.6 A and the voltage across the capacitor is 200 V. Calculate EACH of the following: (10)

(i) the value of the capacitance;

(ii) the resistance and inductance of the coil;

(iii) the power taken from the supply;

(iv) the circuit power factor.

(a) Why is it important to maintain high efficiency of operation and low values of voltage regulation for power transformers? (6)

(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 Ω and 0.01Ω respectively, and the corresponding leakage reactances are 1.1 Ω and 0.035 Ω 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. (10)

(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? (6)

(b) A 3 ph, 440 V, 60 Hz 8 pole induction motor runs at a power factor of 0.85 lag and drives a load of 8 kW at a speed of 14.4 rev/sec. The stator loss is 1 kW and the rotational losses (windage and friction) amount to 0.8 kW. Calculate EACH of the following: (10)

(i) the synchronous speed;

(ii) the rotor copper loss;

(iii) the input power to the motor;

(iv) the motor current.

(a) With the aid of delta and star connection diagrams, state the basic equation from which the delta-star and star-delta conversion equation can be derived (6)

(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 there is a resistor of 0.3 ohm.

Battery A 105V, internal resistance 0.25 ohm

Battery B 100V, internal resistance 0.2 ohm

Battery C 95V, internal resistance 0.25 ohm

Determine the current values in the two resistors and the power dissipated by them. (10)

Differentiate between half and full wave rectification. State where half wave rectification may be used and the purpose for which it is not well adapted. Sketch a bridge connection by which full wave rectification may be obtained. (16)

(a) Describe with the aid of a simple sketch the arrangement of the three-phase winding of an alternator showing the neutral point. (6)

(b) Explain why for most ships the neutral point is insulated. (5)

(c) Explain why in some installation the neutral point is Earthed. (5)

(a) State the necessary conditions required prior to the synchronizing of electrical alternators. (4)

(b) Describe the type of cumulative damage that may be caused when alternators are incorrectly synchronized. (4)

(c) Explain how the damage referred to in (b) can be avoided / reduced. (4)

(d) For two alternators operating in parallel state the consequences of: (4)

(i) Reduced torque from the prime mover of one machine.

(ii) Reduced excitation on one machine.

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

(a) Rectifier circuit (6)

(b) Amplifier circuit (5)

(c) Oscillator circuit (5)

With reference to U.M.S. operation:

(a) State with reasons the essential requirements for unattended machinery spaces. (8)

(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. (8)

(a) What are the factors on which the speed of a motor depends? Discuss them for series and shunt motors. (6)

(b) A shunt motor supplied at 230 V runs at 900 rpm. When the armature current is 30 A, the resistance of the armature circuit is 0.4 Ω, calculate the resistance required in series with the armature circuit to reduce the speed to 500 rpm. Assume that the armature current is 25 Amps. (10)

(a) Derive an expression for the emf induced in an A.C. generator. (6)

(b) A 3000 KVA, 6-pole alternator runs at 1000 r.p.m. in parallel with other machines on 3300V bus-bars. The synchronous reactance is 25%. Calculate the synchronizing power for one mechanical degree of displacement and the corresponding synchronizing torque. (10)

(a) Explain the purpose of interpoles and state their magnetic polarity relative to the main poles of both generators and motors. (6)

(b) A 200V, long-shunt compound-wound generator has a full-load output of 20kW. The various resistances are as follows: armature (including brush contact) 0.15 ohm, series field 0.025 ohm, interpole field 0.028 ohm, shunt field (including the field-regulator resistance) 115 ohm. The iron losses at full load are 780W, and the friction and windage losses 590W. Calculate the efficiency at full load. (10)

(a) What are the factors which determine the synchronous speed of a motor? (6)

(b) A 72 KVA transformer supplies

(i) a heating and lighting load of 12 KW at unity power factor

(ii) a motor load of 70 kVA at 0.766 (lagging) power factor.

Calculate the minimum rating of the power-factor improvement capacitors which must be connected in the circuit the ensure that the transformer does not become overloaded. (10)

(a) Compare the effectiveness of a current limiting circuit breaker with that of a HRC fuse. (6)

(b) Evaluate for a frequency of 15 kHz, the amplification and the phase difference between input and output signals of a voltage amplifier using a triode having an amplification factor of 48 and a mutual conductance of 1.2 mA/V with an anode-load resistant of 160 kΩ. The output p.d. is fed by a coupling capacitor of negligible reactance to a subsequent circuit of resistance 480 kΩ and the total shunt capacitance is 90 μF. (10)

(a) Explain the meaning of the term power factor correction.

(b) State TWO advantages of power factor correction.

(c) Explain, with the aid of a circuit diagram, how power factor correction can be effected in a three-phase circuit using capacitors.

(d) Explain ONE method other than the use of capacitors by means of which power factor correction may be effected.

(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 cases the neutral point is insulated.

(c) Explain why in some installation the neutral point is Earthed.

(a) State the necessary conditions required prior to the synchronizing of electrical alternators.

(b) Describe the type of cumulative damage that may be caused when alternators are incorrectly synchronized.

(c) Explain how the damage referred to in (b) can be avoided / reduced.

(d) If two alternators operating in parallel what are the consequences of:

(i) Reduced torque from the prime mover of one machine.

(ii) Reduced excitation on one machine.

(a) What is intrinsic electric safety?

(b) Can live maintenance be done on intrinsically safe circuits?

(c) Describe intrinsically safe equipment used onboard ship.

(a) (i) Sketch a diagrammatic arrangement of a static or self-excited alternator.

(ii) Describe the operation of the self-excited alternator.

(c) State why the voltage dip is less in the self-excited alternator than in brushless or conventional alternators.

(a) What are the factors on which the speed of a motor depends? Discuss them for series and shunt motors. (6)

(b) A shunt motor supplied at 230 V runs at 900 rpm. When the armature current is 30 A, the resistance of the armature circuit is 0.4 Ω, calculate the resistance required in series with the armature circuit to reduce the speed to 500 rpm. Assume that the armature Current is 25 Amps. (10)

Two three phase 415 V alternators supply a ship’s load comprising:

• lighting totalling 800 kW at unity power factor; and
• motors totalling 1700 kW at power factor 0.7 lag.

One alternator supplies 1400 kW at power factor 0.75 lag.

(a) Calculate EACH of the following for the other alternator: (16)

(i) the KVA output;

(ii) the power factor;

(iii) the line output current.

(a) With reference to an a.c. generator used in marine practice derive an expression for the frequency of the generated e.m.f. in terms of the speed of the machine and the number of poles. (6)

(b) A 200V, long-shunt compound-wound generator has a full-load output of 20KW. The various resistances are as follows: armature (including brush contact) 0.15 Ω, series field 0.025 Ω, interpole field 0.028 Ω, shunt field (including the field-regulating resistance) 115 Ω. The iron losses at full load are 780W, and the friction and windage losses 590W. Calculate the efficiency at full load. (10)

(a) What are the factors which determine the synchronous speed of a motor?

(b) A 72 kVA transformer supplies

(i) a heating and lighting load of 12 kW at unity power factor,

(ii) a motor load of 70 kVA at 0.766 (lagging) power factor. Calculate the minimum rating of the power factor improvement capacitor which must be connected in the circuit to ensure that the transformer does not become overloaded. (10)

(a) Compare the effectiveness of a current limiting circuit breaker with that of a HRC fuse (6)

(b) Evaluate for a frequency of 15 kHz, the amplification and the phase difference between input and output signals of a voltage amplifier using a triode having an amplification factor of 48 and an mutual conductance of 1.2 mA/V with an anode-load resistant of 160 KΩ. The output p.d. is fed by a coupling capacitor of negligible reactance to a subsequent circuit of resistance 480 KΩ and the total shunt capacitance is 90μ F. (10)

With reference to shipboard electrical distribution systems:

(a) describe the meaning of the term earth fault;

(b) explain why an insulated neutral is preferred for low voltage systems;

(c) sketch a circuit diagram of one arrangement for detecting phase to earth faults for a star neutral earthing resistor (NER)

(d) How is the ohmic value of a NER calculated to limit the earth fault current to the full load rating of a three-phase neutral earthed a.c. generator.

In the event of 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.

With reference to squirrel cage induction, electric motor:

(a) Describe the construction of such a motor.

(b) Sketch the torque against speed curve of such a motor.

(c) Describe a method employed by a retrofitted device used to improve the part load performance of an induction motor.

With reference to a 3 speed a.c. cage motor driven cargo winch:

(a) Sketch a circuit diagram for a pole change motor;

(b) Describe how speed change and braking are achieved.

With reference to the condition monitoring of electrical machinery:

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

(b) Explain how the parameters are monitored and what defects may be revealed.

(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 (6)

(b) A total load of 8000 kW at 0.8 power factor is supplied by two alternators in parallel. One alternator supplies 6000kW at 0.9 power factor. Find the kVA rating of the other alternator and the power factor. (10)

(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? (6)

(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. (10)

(a) Why is it important to maintain high efficiency of operation and low values of voltage regulation for power transformers (6)

(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 Ω and 0.01 Ω respectively and the curresponding leakage reactances are 1.1Ω and 0.035Ω respectively. The supply voltage is 2200V. Calculate (10)

(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 0.8 lagging and 0.8 leading

(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 related 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 35Ω. When connected to a 220V, 50Hz, 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 0.7A. 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.

(a) With the aid of delta and star connection diagrams, state the basic equation from which the delta-star and 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 there is a resistor of 0.3 ohm.

Battery A 105V, internal resistance 0.25 ohm

Battery B 100V, internal resistance 0.2 ohm

Battery C 95V, internal resistance 0.25 ohm

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

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

(a) Rectifier circuit

(b) Amplifier circuit

(c) Oscillator circuit.

With reference to U.M.S. operation:

(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.

Explain the matching of an induction electric motor to a pump required for main circulating duty, with the aid of pump characteristic and torque/slip diagrams.

With reference to a three-phase shipboard electrical distribution system:

(a) Enumerate the advantages of an insulated neutral system

(b) Enumerate the disadvantages of an insulated neutral system

(c) Describe how the Earthed neutral system is Earthed.

(d) Compare the use of an insulated neutral system as opposed to the use of an Earthed neutral system with regard to the risk of electric shock from either system.

(a) Sketch a magnetic overload device incorporating a dashpot and explain how the current and time settings of the device may be varied.

(b) With the aid of a sketch, outline the essential features of a three stage "preferential tripping" scheme for the main generators of a ship.

(a) Describe Ingress protection rating and types of insulation. (6)

(b) A total load of 8000 kW at 0.8 power factor is supplied by two alternators in parallel. One alternator supplies 6000kW at 0.9 power factor. Find the kVA rating of the other alternator and the power factor. (10)

(a) Electric motors contain a stationary member as well as a rotating member. For each of the following machines, identify in which part of the motor three field winding and the armature winding is located: three phase induction motor, three phase synchronous motor, D.C. motor. (6)

(b) A 220 V, D.C. shunt motor has an armature resistance of 0.5 ohm and an armature current of 40 A on full load. Determine the reduction in flux necessary for a 50 per cent reduction in speed. The torque for both conditions can be assumed to remain constant. (10)

(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? (6)

(b) A 440 V load of 400 kW at 0.8 (lagging) power factor is jointly supplied by two alternators A and B. The kW load on A is 150 kW and the kVAr load on B is 150 kVAr (lagging). Determine the kW load on B, the kWAr load on A, the power factor of operation on each machine and the current loading of each machine. (10)

(a) Explain the preference for a 60 Hz system. Describe the dangers of running a 50 Hz system from a 60 Hz supply. (6)

(b) A ring-main, 900m long, is supplied at a point A at a p.d. of 220V. At a point B, 240m from A, a load of 45A is drawn from the main, and at a point C, 580m from A, measured in some direction, a load of 78A is taken from the main. If the resistance of the main (lead and return) is 0.25 ohm per kilometre, calculate the current which will flow in each direction round the main from the supply point A and the potential difference across the main, at the load where it is lowest. (10)

(a) (i) What is direct-connected alternator? (3)

(ii) How is a direct-connected exciter arranged in an alternator? (3)

(b) Find the synchronous impedance and reactance of an alternator in which a given field current produces an armature current of 200 A on short circuit and a generated e.m.f. of 50V on open-circuit. The armature resistance is 0.1 ohm. To what induced voltage must the alternator be excited if it is to deliver a load of 100 A at a p.f. of 0.8 lagging, with a terminal voltage of 200 V. (10)

(a) Explain the meaning of the term power factor correction.

(b) State TWO advantages of power factor correction.

(c) Explain, with the aid of a circuit diagram, how power factor correction can be effected in a three phase circuit using capacitors.

(d) Explain one method other than the use of capacitors by means of which power factor correction may be effected.

(a) Describe with the aid of a simple sketch the arrangement of the three-phase winding of an alternator showing the neutral point. (6)

(b) Explain why for most ships the neutral point is insulated. (5)

(c) Explain why in some installation the neutral point is Earthed. (5)

(a) State the necessary conditions required prior to the synchronizing of electrical alternators. (4)

(b) Describe the type of cumulative damage that may be caused when alternators are incorrectly synchronized. (4)

(c) Explain how the damage referred to in (b) can be avoided / reduced. (4)

(d) For two alternators operating in parallel state the consequences of: (4)

(i) Reduced torque from the prime mover of one machine.

(ii) Reduced excitation on one machine.

(a) What is intrinsic electric safety? (6)

(b) Can live maintenance be done on intrinsically safe circuits? (5)

(c) Describe intrinsically safe equipment used on board ship. (5)

(a) (i) Sketch a diagrammatic arrangement of a static or self-excited alternator. (5)

(ii) Describe the operation of the self-excited alternator. (5)

(b) State why the voltage dip is less in the self-excited alternator than in brushless or conventional alternators. (6)

(a) What are the factors on which the speed of a motor depends? Discuss them for series and shunt motors. (6)

(b) A shunt motor supplied at 230 V runs at 900 rpm. When the armature current is 30 A, the resistance of the armature circuit is 0.4 Ω, calculate the resistance required in series with the armature circuit to reduce the speed to 500 rpm. Assume that the armature current is 25 Amps. (10)

Two three phase 415 V alternators supply a ship’s load comprising:

• lighting totalling 800 kW at unity power factor; and
• motors totalling 1700 kW at power factor 0.7 lag.

One alternator supplies 1400 kW at power factor 0.75 lag.

(a) Calculate EACH of the following for the other alternator: (16)

(i) the KVA output;

(ii) the power factor;

(iii) the line output current.

(a) With reference to an A.C. generator used in marine practice derive an expression for the frequency of the generated e.m.f. in terms of the speed of the machine and the number of poles. (6)

(b) A 200V, long-shunt compound-wound generator has a full-load output of 20kW. The various resistances are as follows: armature (including brush contact) 0.15 ohm, series field 0.025 ohm, interpole field 0.028 ohm, shunt field (including the field-regulator resistance) 115 ohm. The iron losses at full load are 780W, and the friction and windage losses 590W. Calculate the efficiency at full load. (10)

(a) What are the factors which determine the synchronous speed of a motor? (6)

(b) A 72 KVA transformer supplies

(i) a heating and lighting load of 12 KW at unity power factor

(ii) a motor load of 70 kVA at 0.766 (lagging) power factor.

Calculate the minimum rating of the power-factor improvement capacitors which must be connected in the circuit the ensure that the transformer does not become overloaded. (10)

(a) Compare the effectiveness of a current limiting circuit breaker with that of a HRC fuse. (6)

(b) Evaluate for a frequency of 15 kHz, the amplification and the phase difference between input and output signals of a voltage amplifier using a triode having an amplification factor of 48 and a mutual conductance of 1.2 mA/V with an anode-load resistant of 160 kΩ. The output p.d. is fed by a coupling capacitor of negligible reactance to a subsequent circuit of resistance 480 kΩ and the total shunt capacitance is 90 μF. (10)

(a) Describe the circuit breaker for an a.c. generator using a sketch to show how arcing is controlled.

(b) Explain the sequence of events that might occur if the breaker opens on a short circuit and state the check you would required following such event.

(c) Give a Safe procedure to follow should a train circuit breaker fail to open under fault condition.

(a) With respect to measuring instruments, what is the difference between analogue and digital measuring instruments. Explain the working principle of each type.

(b) Describe with the aid of simple sketches one analogue and one digital measuring instrument you have used onboard.

With respect to power transformers, kindly explain the following protections

(a) Overload protection

(b) Overcurrent protection for phase faults

(c) Earth Fault protection

(d) Differential protection

(e) Directional protection

(a) In a.c. generators, voltage dip occurs in two stages.

(i) Sketch a voltage-time graph showing the pattern of voltage dip.

(ii) Referring to this graph, state with reasons the effect on the electrical system of a small power installation when a large load is suddenly switched.

(b) Explain EACH of the following categories of voltage control:

(i) Error operated;

(ii) Functional.

In some circumstances electrical current may be induced in the shafting of rotating machinery.

(a) State the problem that may be caused by this current.

(b) Explain with the aid of sketches, how currents may be avoided or reduced in the following instances

(i) d.c. mahcines

(ii) main shafting fitted with a bronze propeller

(a) Explain the significance of the root mean square value of an alternating current or voltage wave form. Define the form factor of such a wave form. (6)

(b) Draw the circuit of Half-wave rectifier and its output waveform. A diode whose internal resistance is 20 Ω is to supply power to 1000 Ω load from 110 V (RMS) source. Calculate (10)

(i) peak load current,

(ii) DC load current,

(iii) AC load current.

(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? (6)

(b) A d.c. motor takes an armature current of 110 A at 480 V. The resistance of the armature circuit is 0.2 Ω. The machine has 6 poles and the armature is lap connected with 864 conductors. The flux per pole is 0.05 Wb. Calculate: (10)

(a) The speed,

(b) The gross torque developed by the armature.

(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) A three-phase induction motor is wound for four poles and is supplied from a 50 Hz system. Calculate:

(i) The synchronous speed.

(ii) The speed of the rotor when the slip is 4 per cent.

(iii) The rotor frequency when the speed of the rotor is 600 r/min.

(a) What is leakage flux as it applies to the iron-core transformer? How is it considered in the analysis of the transformer? (6) x

(b) Three conductors fitted side by side in the stator of a salient-pole alternator. Each generates a maximum voltage of 200V (sinusoidal). The angle subtended at the centre of the stator between adjacent conductors is 20 electrical degrees. If the three conductors are connected in series, find: (10)

(i) the r.m.s. value of the effective voltage and

(ii) the 'breadth factor'. Using the theory that is the basis of this problem, give one reason why three-phase current has been introduced.

(a) What are the factors which determine the synchronous speed of a motor? (6)

(b) A twelve-pole, three-phase, delta-connected alternator runs at 600 rev/min and supplies a balanced star-connected load. Each phase of the load is a coil of resistance 35 ohm and inductive reactance 25 ohm. The line terminal voltage of the alternator is 440V. Determine (10)

(i) frequency of supply,

(ii) current in each coil,

(iii) current in each phase of the alternator,

(iv) total power supplied to the load.

Discuss the criteria of the classification of marine high voltage for A.C. and D.C. Systems. Sketch a Ships high voltage distribution system and explain its features. Discuss the various methods of testing the insulation of HV system. Mention the significance of PI test, why 3 terminals insulation testers are used in HV insulation measurements. (16)

Briefly describe following with respect to protective relaying:

(a) Principle of operation and characteristics of induction type relays. (6)

(b) Static and digital relays. (5)

(c) Protection of alternators, motors, transformer and busbar. (5)

(a) Explain how the efficiency and regulation of a transformer can be assessed by open circuit and short circuit tests? (10)

(b) What is meant by equivalent resistance? (6)

Discuss the fundamental principles and advantages of electrical propulsion systems in marine vessels compared to conventional mechanical propulsion. What are some of the components that make up an electrical propulsion system? (16)

(a) Briefly explain the principle of Operation of induction Motors (4)

(b) What is slip for an induction motor? (4)

(c) Draw a simple ladder logic diagram of star delta starting of an induction motor. (8)

(a) Describe International protection rating and types of insulation. (6)

(b) A total load of 8000 kW at 0.8 power factor is supplied by two alternators in parallel. One alternator supplies 6000kW at 0.9 power factor. Find the kVA rating of the other alternator and the power factor. (10)

(a) D.C. motors are used where very high torque and/or precise speed control is required. How does the control of magnetic field flux and armature current relate to the starting characteristics of a D.C. motor in such applications? (6)

(b) A 220 V, D.C. shunt motor has an armature resistance of 0.5 ohm and an armature current of 40 A on full load. Determine the reduction in flux necessary for a 50 per cent reduction in speed, the torque for both conditions can be assumed to remain constant. (10)

(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? (6)

(b) A 440 V load of 400 kW at 0.8 (lagging) power factor is jointly supplied by two alternators A and B. The kW load on A is 150 kW and the kVAr load on B is 150 kVAr (lagging).

Determine the kW load on B, the kVAr load on A, the power factor of operation on each machine and the current loading of each machine. (10)

(a) Explain the preference for a 60 Hz system. Describe the dangers of running a 50 Hz system from a 60 Hz supply. (6)

(b) A ring-main, 900m long, is supplied at a point A at a p.d. of 220V. At a point B, 240m from A, a load of 45A is drawn from the main, and at a point C, 580m from A, measured in same direction, a load of 78A is taken from the main. If the resistance of the main (lead and return) is 0.25 ohm per kilometre, calculate the current which will flow in each section of round the main from the supply point A and the potential difference across the mains at the load where it is lowest. (10)

(a) (i) What is direct-connected alternator? (3)

(ii) How is a direct-connected exciter arranged in an alternator? (3)

(b) Find the synchronous impedance and reactance of an alternator in which a given field current produces an armature current of 200 A on short circuit and a generated e.m.f. of 50V on open circuit. The armature resistance is 0.1 ohm. To what induced voltage must the alternator be excited if it is to deliver a load of 100 A at a p.f. of 0.8 lagging, with a terminal voltage of 200 V. (10)

Differentiate between half and full wave rectification. State where half wave rectification may be used and the purpose for which it is not well adapted. Sketch a bridge connection by which full wave rectification may be obtained. (16)

(a) Describe with the aid of a simple sketch the arrangement of the three-phase winding of an alternator showing the neutral point. (6)

(b) Explain why for most ships the neutral point is insulated. (5)

(c) Explain why in some installation the neutral point is Earthed? (5)

(a) State the necessary conditions required prior to the synchronizing of electrical alternators. (4)

(b) Describe the type of cumulative damage that may be caused when alternators are incorrectly synchronized. (4)

(c) Explain how the damage referred to in (b) can be avoided / reduced. (4)

(d) For two alternators operating in parallel state the consequences of: (4)

(i) Reduced torque from the prime mover of one machine.

(ii) Reduced excitation on one machine.

(a) What is intrinsic electric safety? (6)

(b) Can live maintenance be done on intrinsically safe circuits? (5)

(c) Describe intrinsically safe equipment used on board ship. (5)

(a) (i) Sketch a diagrammatic arrangement of a static or self-excited alternator. (5)

(ii) Describe the operation of the self-excited alternator. (5)

(b) State why the voltage dip is less in the self-excited alternator than in brushless or conventional alternators. (6)

(a) What are factors on which the speed of a motor depends? Discuss them for series and shunt motors. (6)

(b) A shunt motor supplied at 230 V runs at 900 rpm. When the armature current is 30 A, the resistance of the armature circuit is 0.4 Ω, calculate the resistance required in series with the armature circuit to reduce the speed to 500 rpm. Assume that the armature current is 25 Amps. (10)

(a) Derive an expression for the emf induced in an A.C. generator. (6)

(b) A 3000 KVA, 6-pole alternator runs at 1000 r.p.m. in parallel with other machines on 3300V bus-bars. The synchronous reactance is 25%. Calculate the synchronizing power for one mechanical degree of displacement and the corresponding synchronizing torque. (10)

(a) Explain the purpose of interpoles and state their magnetic polarity relative to the main poles of both generators and motors. (6)

(b) A 200V, long-shunt compound-wound generator has a full-load output of 20kW. The various resistances are as follows: armature (including brush contact) 0.15 ohm, series field 0.025 ohm, interpole field 0.028 ohm, shunt field (including the field-regulator resistance) 115 ohm. The iron losses at full load are 780W, and the friction and windage losses 590W. Calculate the efficiency at full load. (10)

(a) What are the factors which determine the synchronous speed of a motor? (6)

(b) A 72 KVA transformer supplies

(i) a heating and lighting load of 12 KW at unity power factor

(ii) a motor load of 70 kVA at 0.766 (lagging) power factor.

Calculate the minimum rating of the power-factor improvement capacitors which must be connected in the circuit the ensure that the transformer does not become overloaded. (10)

(a) Compare the effectiveness of a current limiting circuit breaker with that of a HRC fuse. (6)

(b) Evaluate for a frequency of 15 kHz, the amplification and the phase difference between input and output signals of a voltage amplifier using a triode having an amplification factor of 48 and a mutual conductance of 1.2 mA/V with an anode-load resistant of 160 kΩ. The output p.d. is fed by a coupling capacitor of negligible reactance to a subsequent circuit of resistance 480 kΩ and the total shunt capacitance is 90 μF. (10)

(a) Briefly explain the principle of Operation of Induction Motors (4)

(b) What is slip for an induction motor? (4)

(c) Draw a simple ladder logic diagram of star delta starting of an induction motor. (8)

What is Zener diode and how does it regulate the voltage? What happens to the series current, load current and Zener current when the D.C. input voltage of a Zener regulator increases? Draw a neat diagram of Zener regulator and explain. (16)

Discuss the criteria of the classification of marine high voltage for A.C. and D.C. Systems. Sketch a Ships high voltage distribution system and explain its features. Discuss the various methods of testing the insulation of HV system. Mention the significance of PI Test, why 3 terminals insulation testers are used in HV insulation measurements? (16)

What are the conditions for producing sustained oscillations? Classify oscillations with respect to frequency range, principle involved, etc. It is possible to produce oscillations with RC networks in phase shift oscillators. Discuss in detail. (16)

What is soft starting of an Induction motor? Describe with a circuit using thyristors used for soft starting. Discuss its advantages and dis-advantages. (16)

(a) Describe International protection rating and types of insulation. (6)

(b) A 72 KVA transformer supplies a heating and lighting load of 12 KW at unity power factor and a motor load of 70 kVA at 0.766 (lagging) power factor: Calculate the minimum rating of the power-factor improvement capacitors which must be connected in the circuit the ensure that the transformer does not become overloaded. (10)

(a) Which of the following three motors has the poorest speed regulation: shunt motor, series Motor or cumulative compound motor? Explain. (6)

(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. (10)

(a) What is back emf? Derive the relation for the back emf and the supplied voltage in terms of armature resistance. (6)

(b) A three-phase induction motor is wound for four poles and is supplied from a 50 Hz system. Calculate. (10)

(i) The synchronous speed:

(ii) The speed of the rotor when the slip is 4 per cent:

(iii) The rotor frequency when the speed of the rotor is 600 r/min.