QUESTIONS

Q1. Dec13,Nov13, June13, Apr13A. 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 operation of this power trip is based & How tripping is activated.Q2. Dec13,Apr12,Mar12Sketch a circuit diagram of an emergency generator power supply system suitable for passenger vessel: including in your diagram essential services supplied. WRT an emergency generator state - 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. Q3. Dec13,July13,Dec12, Apr12, Mar12Explain the effect of reduced voltage on standard cage motors wrt EACH of the following:A.Burn out; B. Starting current; C. Starting torque; D. Speed.Q4. Dec13, July13,June13, Mar13,Octo12, Apr12,Feb12,Apr13Differentiate with the aid of simple sketches between following types of electronic circuits: A. Rectifier circuit; B. Amplifier circuit; C. Oscillator circuit.Q5. Dec13, Nov13, July13, Apr12WRT 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. Nov13A. Describe a brush less alternator with a.c. exciter static A.V.R.; B. State the output voltage characteristics for this type of machine.

Q7. Nov13With the aid of sketch describe main features & principle of operation of a D.C. moving Coil meter. If such a meter is designed to give full scale deflection with 150 mA, State how it May be adapted; As an ammeter to read up to 150 A; (ii) As a voltmeter to read up to 150 V.; No calculations are required.

Q8. Nov13, Jan13WRT preferential tripping in a marine electrical distribution system A. State why this facility is required; B. With aid of a sketch, describe a typical arrangement to provide 3 stages of tripping as an instantaneous protection against short circuit.

Q9. Sept13, Aug13,June12,Jan14A. (i) Discuss the various hazards & problems which are associated with electric cable Insulation in event of fire. (ii) Suggest remedies; B. State how spread of fire may be reduced by the method used for installing electric cables. Q10. Sept13, Aug13, June12, Jan14Differentiate between squirrel cage & wound rotor motor of 3 phases: a.c. induction. In respect of the followingA. Rotor construction, B. Torque characteristic, C. Speed variation.

Q11. Sept13, Mar13,Jan14In 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.Q12. Sept13, Aug13, Sept12,June12,Apr14,Mar14The direct on line start of squirrel cage motor is used for most electrical drives on a.c. powered. ShipsDescribe with sketches as necessary one method of overcoming each of the following Problems - A. High starting current; B. Low starting torque. Q13. Sept13, Mar13,Octo12,Feb12A. 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 & 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.

Q14. Aug13, June13,Sept12,June12,Mar14WRT an emergency source of electrical power in cargo ships:- A. Describe a typical power source; B. Give a typical list of essential services, which must be supplied simultaneously; C. Explain how emergency installation can be periodically tested.

Q15. July13(a) In a.c. generators, voltage dip occurs in 2 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 installationwhen a large load is suddenly switched on.(b) Explain EACH of the following categories of voltage control: (i) Error operated; (ii) Functional.Q16. July13Which of the following devices will prevent a DC generator from becoming motorized? A. Over current relay B. Motorization trip C. Reverse power relay D. Reverse current relay. Give a detailed explanations as to why other options were not considered.

Q17. June13, Octo12,Apr13(a) (i) Describe with aid of a sketch operation of a synchroscope. ii) State information obtained from it. (b) Suggest a substitute in the event of synchroscope & stand by light failure.

Q18. June13, Mar13, Octo12,Feb12,Apr13List at least 2 factors that cause deterioration of the frequency response of a transistor amplifier. Explain how each factor affects the performance of the amplifier & the portion of the frequency range where it is effective.

Q19. Mar13A. What are the causes of overheating of an induction motor?B. What preventive measures are provided against damage to an induction motor in installed condition?C. What is the purpose of fuse back up protection provided to an induction motor?D. How does an induction motor develop torque?E. What is the condition to be satisfied for achieving maximum running torque in an induction motor?Q20. Jan13Sketch & describe the method of speed control of synchronous motors by variable frequency. State the advantages of this method over the other methods of speed control.Q21. Jan13, Dec12What is a marine high voltage system? Sketch & describe a shipboard high voltage switch board & its protective devices.

Q22. Jan13, Dec12What is a soft starting of an Induction motor? Describe with a circuit using a thyristors used for soft starting. Discuss its advantages & dis-advantages. Q23. Jan13(a) Sketch a main engine shaft driven generator arrangement with - an electronic system for frequency correction. (b)Describe the operation of the generator arrangement sketched in (a).

Q24. Nov12,Feb14(a) Give a brief outline of the care maintenance that should be given to the stator and rotor of an A.C. generator; (b) Explain what is likely to occur if the driving power of one A.C. generator suddenly fails when two generators are running in parallel. What safety devices are usually provided for such events? Q25. Nov12, Feb14Compare methods of obtaining speed regulation of 3-phase induction motor generally used in tankers by means of: Rotor resistance; Cascade system; Pole-changing. Give examples where each system may be employed with advantage.

Q26. Nov12, Feb14 (a) Explain how the efficiency and regulation of a transformer can be assessed by open circuit and short circuit tests?;What is meant by equivalent resistance? Q27. Nov12, Feb14 WRT a 3 speed a.c. cage motor driven cargo winch: Sketch a circuit diagram for a pole change motor; Describe how speed change & braking are achieved.

Q28. Nov12, Feb14,Jan14 WRT the condition monitoring of electrical machinery: State TWO important parameters that may be recorded; Explain how the parameters are measured and what defects may be revealed.

Q20. Sept12,Mar14WRT the provision of a shore electrical supply to a ship: (a)Sketch an arrangement for taking A.C. shore supply & checks to be carried out prior Taking shore connection?(b)Describe the method of safely connecting the arrangement sketched in (a) to the shore Supply?Q30. Sept12, Mar14WRT electronic control systems: Draw a simple block diagram for temperature control. Describe each component shown in the diagram in (a).

Q31. Sept12,June12,Apr14, Mar14,Jan14Diesel electric propulsion is now being chosen as the power plant for an increasingly wide variety of vessels. Sketch a simple layout of such an installation. Explain the advantages of selecting such a plant.Q32. Mar12,Apr14(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) For two alternators operating in parallel state the consequences of: (i) Reduced torque from the prime mover of one machine. (ii)Reduced excitation on one machine.

Q33. Apr14(a) What is Open loop & Close loop? Discuss the relative advantage of each.(b) Sketch a practical close loop system & describe the loop explaining the meaning of the Terms:(i)Servo-motor, (ii)Feedback, (iii)Sensor Element.Q34. Apr14Describe how a self-excited AC generator would work.Q35. Apr14Describe A. A safety lamp approved as part of slips statutory equipment LIFEBUOY SELF IGNITING LIGHTS; B. A self- igniting lamp suitable for attachment to a lifebuoy; C. State the attention required to maintain them in a satisfactory working condition.Q36.Apr13Sketch a standby battery charging/discharging circuit. Describe the circuit sketched, making special reference to how battery charge is maintained and how it operates upon loss of main power.

NUMERICALSQ1. Dec13, July13,Feb14A. 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. Feb12B. 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.

Q2. Dec13, July13,Feb12, Feb14A. 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 Lagging and leading; (iii) The secondary terminal voltages corresponding to (i) & (ii) Q3. Dec13,Feb12, Feb14 A. What is silicon controlled rectifier (SCR)? How is 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.

Q4. Dec13,Feb12,Feb14 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;Q5. Dec13,Feb12, Feb14 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 0.11Calculate the efficiencies at - Full load;

Q6. Nov13, Aug13, Mar13,Dec12,Sept12,Apr12,Mar14,Jan14A. 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; 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. Q7. Nov13,Dec12,Mar12, Mar14A. Sketch an arrangement showing the principal of proportional plus integral (P+I) control loop; B. Compare the series and parallel resonance circuits. Find the frequency at which the following circuit resonates.Q8. Nov13, Dec12, Mar14A. Explain the potential hazards if liquid-cooled transformers are used.B. What are the losses in transformers? Mention the various factors which affect these losses. In a 25 KVA, 3300/233 V, single phase transformer, the iron and full-load Cu. Losses are respectively 350 and 400 watts. Calculate the efficiency at half-full load, 0.8 power factor.

Q9. Nov13, Aug13, Mar13, Dec12,Sept12, Mar14,Jan14 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. 2supply 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.

Q10. Nov13, Aug13,Sept12, Mar14,Jan14 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,Battery A 105 V, Internal resistance 0.25 ohmBattery B 100 V, Internal resistance 0.2 ohmBattery C 95 V, Internal resistance 0.25 ohmDetermine the current values in the two resistors and the power dissipated by them

Q11. Sept13,June12 A. What are factors on which the speed of a motor depends? Discuss them for series and shunt motors. 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 , 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.Q12. Sept13, Jan13 A. Describe the possible causes and the effect of running a three phase motor with one phase open circuited.B. Jan13, Nov12,Octo12,June12, Mar12A 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.

Q13. Sept13,June12 A. Sketch a simplified circuit of a reverse power relay explain why there is a time delay incorporatedbefore the reverse power relay operates; B. Apr14A 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 A. frequency of supply, B. current in each coil, C. current in each phase of the alternator, D. total power supplied to the load.Q14. Sept13,June12 A. Describe the effects of changes in speed, rotor current and torque as load is applied to an induction motor.B. How does the motor adjust its stator current with changes in mechanical load?; A shunt motor runs at 900 rev/min when connected to a 440 V supply, the armature current being 60 A and armature resistance 0.4 ohm. At what speed will it run on a 220 V supply with an current of 40 A. Assume 60 percent reduction in flux for the 220 V connection.

Q15. Aug13, Mar13, Jan13, Nov12,Sept12,Apr12,Jan14 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? ; 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.

Q16. Aug13, Mar13, Jan13,Nov12,Sept12,Jan14 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 reactances 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.

Q17. July13 The armature and field resistances of a 220V shunt motor are 0.25 and 110 ohms respectively & when running on no load, the motor takes 6A, calculate the losses attributable to iron, friction and windageand assuming this value to rmain constant on loads, determine the efficiency when the current supplied is 62A.Q18. July13 A 3-phase transformer has 560 turns on the primary and 42 turns on the secondary. The primary windings are connected to a line voltage of 6.6 Kv, calculated the secondary line voltage when the transformer is connected: (A) Star Delta B) Delta-Star

Q19. July132 shunt generators X & Y work in parallel. their external characteristics may be assumed to be liner over their normal working range. The terminal voltage of X falls from 265V on no load to 230V. When delivering 350A to the bus bars, while the voltage falls from 270V on no load to 240V when delivering 400A to the bus bars, calculate the current which each machines delivers when they share a common load of 500A, what is the bus bar voltage under this condition and power delivered by each machine?

Q20. June13 (a) What are the characteristics of PN junction diode? Point out its specifications. Also point out the significance of dynamic and static resistances.(b)Draw the circuit of Half-wave rectifier and its output waveform. A diode whose internal resistance is 20 is to supply power to 1000 load from 110 V (RMS) source. Calculate (i) peak load current, (ii) DC load current, (iii) AC load current.

Q21. June13, Octo12,Mar12 Describe the no-load saturation characteristic of a.d.c. generator. (6)A 4-pole machine running at 1500 r.p.m. has an armature with 80 skits abd 6 conductors per pole. The flux per pole is 6 x 10 lines. Determine the terminal e.m.f. of d.c. generator if the coils are lap connected. If the current per conductor is 100 Amps, determine the electrical power.

Q22. June13 What is a commutator? Discuss its rectifying action in detail.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.Q23. June13 Discuss different methods of speed control of a d.c. series motor by adjusting field ampere turns.(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 and shunt field resistance is 230 Calculate the drop in speed when the motor is loaded and takes the line current of 41 amperes. Neglect armature reaction.

Q24. June13 Why is a synchronous motor not self stating. What are the various ways in which it can be started ?A 500V, single phase synchronous motor gives a net output mechanical power of 7.46Kw and operates at 0.9 pf lagging, Its effective resistance is () the iron and friction losses are 500w and excitation losses are 800w, calculates the armature current and the commercial efficiency.Q25. Jan13, Nov12 What is meant by i.)Voltage Stabilization, ii.) Filter choke, iii.) Impedance, iv.) Rectification, vi.) Grid bias voltageQ26. Jan13, Nov12,Octo12,June12,Mar12 (a) Which of the following three motors has the poorest speed regulation: shunt motor, series Motor or cumulative compound motor? Explain.NUMERICAL Q12.

Q27. Apr14 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 terms, Reactive terms, i.e. Capacitive reactance and inductance reactance.B. A resistance of 130 and a capacitor of 30F are connected in parallel across a 230 Volt, 50Hz supply. Find the current in each component, total current, phase angle and the power consumed.Q28. Apr14 A. Explain the working principal of a 3 phase induction motor. What are the various types of rotors?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.Q29. Apr14Sketch a graph of starting current, and torque against the speed of rotation for a single cage motor.B. A 230V 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 0.15Ohm and the shunt field resistance is 220Ohm. 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.Q30. Apr14 A. Compare the effectiveness of a current limiting circuit breaker with that of a HRC fuse.B. A coil having a resistance of 10Ohm, and an inductance of 0.15H is connected in series with a capacitor across a 100V, 50Hz 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.