# Canadian First Class ME  ElectroTech

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###### Transport Canada has ask us to advise users of this webpage to keep in mind that these questions are not the exact questions found in their exams. Martin's Marine Engineering Page - www.dieselduck.net is not affiliated with Transport Canada and these questions have been gathered from various sources.

1. To find the resistance of a coil, an ammeter and a voltmeter are used.  The ammeter which has a resistance of 0.005 ohm, is connected in series with the coil, and the voltmeter, which has a resistance of 5000 ohms is connected across the ends of the coil.  When the voltmeter registers 210 volts the ammeter registers 3 amperes.  The resistance of the coil was then calculated from the voltmeter reading divided by the ammeter reading.  Calculate the % error in this value.

Ans: P47 V2

2. Given a meter movement that has full scale deflection current of 0.015 A and 5 ohms resistance, calculate the shunt resistor required to use this meter in a 20 ampere circuit

and also the multiplier resistor that would be necessary to use it in a 50 volt circuit.

Ans: P8 V2

3. Two lamps with the following characteristics are to be connected in series across a 230 volt supply. A lamp is 110 volts and 40 watts whilst the other is 100 volts and 150 watts. Indicate by a sketch and calculation how they can be connected so that they operate within their characteristics.

note: resistors may be used to complete the circuit.

Ans: P70 V2

4. Calculate the current through the 2 ohm resistor.

insert diagram here

Ans: P69 V1

5. A battery of six cells in series, each cell has an e.m.f. of 1.5 volts and internal resistance of 0.5 ohms, is connected to resistances of 6 ohms, 12 ohms separately at first and then with the two resistances in parallel across the battery terminals.  Calculate the current through each resistance in each of the cases.

Ans: P34 V1

6. Six electric cells are connected together in series, the e.m.f. of each cell is 1.2 volts and it's internal resistance is 0.4 ohms.  Three wires A, B, and C whose resistances are 5, 40 and 200 ohms respectively, can be connected between the battery terminals.

a) Determine the current which flows when each wire is inserted separately

b) determine the current which flows when they are inserted together as a parallel group

Ans: P25 V1

7. A parallel circuit consists of a branch "A" of resistance 10 ohms, inductance 38 mH and copacitance 312.8 uF, and branch B has negligible resistance and inductive reactance of 12 ohms.  Derive graphically the total current and its phase angle, if the system is connected to a 440 V  50 Hz supply.

8. A lead wire and a copper wire are connected together in parallel.  The currents flowing in the wires are in the ratio of 38 : 40 respectively and the lead wire is 60% longer than the copper wire.  The ratio of the specific resistances of the wires are: lead to copper 208 : 16.  Find the ratio of the cross sectional area of the lead wire to that of copper.

Ans: P51 V2

9. An iron conductor and an aluminum conductor are connected in parallel to a supply.  The iron conductor is 10% longer and half the diameter of the aluminum conductor.  Given that the ratio of the resistivities of iron to aluminum is 40 : 13 find the ratio of the currents in the two conductors.

10. A wire is 60 meters long and weight of 200 grams. A second wire is 70 feet long and weighs 6 oz.  The specific resistance of the second wire is 10% less than that of the first, and the material of the first wire is 2% less in weight per cu. inch than the material of the second wire. Find the ratio of resistance of the second wire to that of the first.

***imperial units?????

Ans: P24 V1

11. An electric heater consists of 8 elements connected in parallel to a 220 volt supply and heats up 10 tonnes of oil 35o C in a 24 hour period.  If the specific heat of the oil is 2.17 kJ/kg oC and the efficiency of the heater is 70% find:

a) the current taken

b) the resistances of one of the elements if they are all of the same value.

Ans: P35 V1

12. An electric heater in a 220 Volt circuit raises the temperature of 3 tonnes of oil by 50 degrees C every 12 hours.  The efficiency of the heater is 80% and the specific heat of oil is 2 kJ/kg oC.  Find:

a) the power consumption in kWhours

b) the current taken

c) the resistance of the heater element

Ans: P86 V1

13. a) Show how the electric potential difference (volt) is related to energy (or work) and quantity of charge.

b) Three capacitors of 2 uF, 3 uF and 5 uF are connected to a 12 volt source, calculate the total charge of the combinations when they are arranged in :

i) parallel

ii) series

Ans: P18 V2

14. State the definition of the ampere in terms of it's coherence as a basic or fundamental unit in the International System of Units (SI).  Using a sketch indicate what is meant by "fringing" and by "leakage" in a magnetic circuit.  What is the magnetic flux density at a distance of 5 cm from a very long straight wire carrying a current of 150 A.  Include units in your numerical solution and show that your answer has the correct units.

note: uo = 4 pi x 10-7

Ans: P34 V2

15. Explain the terms "fringing" and "leaking" when related to a magnetic circuit.  A magnetic circuit is built up of rectangular metal plates 60 mm wide, having a combined depth of 80 mm and with the insulating material between the laminations accounting for 10% of the depth.  The circuit has a mean length of 1.8 m with an air gap of length 3 mm and a cross sectional area of 500 mm2.  Assume a leakage factor of 1.1, the relative permeability of iron as 2500 and the permeability of space as 4 pi x 10-7.  Calculate the magnetomotive force required to produce a flux of 0.006 Wb across the air gap.

Ans: P6 V1

16. A coil of 200 turns is rotated at 1200 RPM between poles of an electromagnet.  Flux density is 0.02 teslas.  Axis of rotation is at right angles to the field.  Effective length of the coil is 0.3 meters, mean width is 0.2 meters. Assuming e.m.f. produced is sinuosoidal, find:

a) maximum value of e.m.f.

b) frequency

Ans: P51 V1

17. A moving coil permanent magnetic instrument has a resistance of 10 ohms and the flux density in the gap is 0.1 teslas.  The coil has 100 turns of wire and is of mean width 300 mm and axial length is 25 mm.  If a p.d. of 50 mV is required for full scale deflection, calculate the controlling torque exerted by the spring.

Ans: P42 V2

18. The following results of measurements were taken at intervals over a half cycle of A.C. voltage:

Time  0  0.45  0.95  1.5   2.1   2.5    3.1   3.9   4.5   5.0 (milliseconds)

Volts 0   20    36   40    37.5   33     32    31    20    0

Calculate:

a) the r.m.s. value of the voltage

b) the frequency of the waveform

Ans: P40 V2

19. A D.C. generator gave the following O.C.C. when driven at 1000 R.P.M.

Field current    (A) 0.2  0.4  0.6  0.8  1.0  1.2  1.4  1.6

Armature voltage (V)  32   58   78   93  104  113  120  125

If the machine is run as a shunt generator at 1000 R.P.M. the shunt field resistance being 100 ohms.  Find:

a) the O.C. voltage

b) the critical value of the shunt field resistance

c) the O.C. voltage if the speed was raised to 1100 R.P.M. the field resistance being kept constant at 100 ohms

20. Express each of the following voltages in phasor notation and locate them on a phasor diagram:

V1 = 212.0  sin (wt + 45  deg)

V2 = 141.4  sin (wt - 90  deg)

V3 = 127.3  cos (wt + 30  deg)

V4 =  85.0  cos (wt - 45  deg)

V5 = 141.4  sin (wt + 180 deg)

Ans: P9 V1

21. Three currents of peak values 10 A, 17.32 A and 20 A respectively meet in a common  conductor.  The 17.32 current lags the 10 A current by 90 deg.  electrical, and leads the 20 A current by 60 electrical degrees.  Find the value of the resultant current giving its phase relation to the 10 A current.

Ans: P66 V1

22. Discuss the relationship between r.m.s., average and Form factor.  A transformer has a primary voltage of 240 V and a secondary of 17200 V.  The primary resistance is 0.00033 oh m

and the secondary resistance is 13 ohms.  The output is 10 kVA.  Find the copper loss at:

c) 1 kVA

Ans P84 V1

23. A single phase power transformer supplies a load of 20 kVA at a power factor of 0.81 lagging.  The iron loss is 200 Watts and the copper loss is 180 Watts.  Find:

a) the efficiency

b) the load at which maximum efficiency occurs

c) if the load is now changed to 30 kVA at a power factor 0.91 lagging find the new efficiency

24. The load taken from a single phase supply consists of:

a) filament lamp load of 10 kW

b) motor load of 80 kVA at 0.8 power factor lagging

Calculate the total load taken from the supply in:

a) kW

b) kVA

c) power factor

Find the mains current if the supply voltage is 250 V. Repeat the problem with the loads using a three phase supply and a voltage of 440 V.

25. More questions like these can be found on Martin's Marine Engineering Page, click to www.dieselduck.net.

25. In the following circuit find:

a) impedance

b) Iline

c) power factor

insert diagram here

Ans: P89 V1

26. A circuit has a resistance of 3 ohms and an inductance of 0.01 henery.  The voltage across this circuit is 60 V and the frequency is 50 Hz.  It is a series circuit. Calculate:

a) impedance

b) line current

c) power factor

d) power absorbed

Ans: P72 V1

27. Find the impedence and power factor of an A.C. circuit consisting of two pieces of apparatus in series.  Piece "A" has a resistance of 2 ohms and inductive reactance of 14 ohms and piece "B" has a resistance of 10 ohms and a capacitive reactance of 6 ohms.

28. An inductive load takes a current of 15A from a 240 V 50 Hz supply and the power absorbed is 2.5 kW.  Calculate:

a) the power factor of the load

b) the resistance of the load

c) the reactance of the load

d) the impedence of the load

Draw a phasor diagram showing voltage drops and current components.

29. A 100 W lamp for a 100 V supply is placed across a 200 V supply.  What values of resistance must be placed in series with it so that it will work under its proper conditions.  If a coil is used instead of the resistor and if the resistance of the coil is small compared to the reactance what is the inductance of the coil.  The frequency is 50 Hz.  What is the total power absorbed in each case?

Ans: P19 V2

30. A coil has a resistance of 15 ohms and an inductance of 0.05 H.  Calculate the impedance and power absorbed by the coil in watt when it is connected to a 100 V 50 Hz A.C. supply.

Ans: P29 V2

31. A coil in an A.C. circuit has a resistance of 15 ohms and an inductance of 0.02 heneries.  If it is connected across a 250 V 50 Hz supply find the power absorbed.

32. An inductive circuit of 50 ohms resistance and 0.02 H inductance is connected in parallel with a capacitor of 25 uF across a 200 V  50 Hz supply.  Find the current taken from the supply and its phase angle 33. Given a 100 V supply with a 70 A current at 60 degrees lagging.  Calculate:

a) the resistance

b) the impedance

c) XL inductive reactance

Ans: P41 V2

34. Given 220 volts, 60 Hz and a series circuit with 50 ohms resistance, 0.01 Henery inductance and 8 uF capacitance, find the line current and power absorbed.

Ans: P85 V1

35. Two coils are connected in series, when 2 amperes D.C. are passed through, the voltage drops are 20 and 30 V respectively.  When 2 amperes A.C. at 40 Hz is passed through, the voltage drops are 140 and 100 volts respectively.  Find the current when the circuit is connected to 230 V 60 Hz.

Ans: P47 V1

36. A coil when connected with a 120 V D.C. supply consumes 600 watts.  When the same coil is connected with a 260 V A.C. supply the consumption is 2400 watts.  Find the inductive reactance of the coil.

Ans: P26 V1

37. A coil has a resistance of 400 ohms and an impedance of 498 ohms connected to a supply of 200 V at 60 Hz.  The coil is then connected in series with a capacitor of 40 uF and across a supply of 240 V at 50 Hz.  Find:

a) the current that flows

b) the voltage drop across the coil and capacitor

Ans: P24 V2

38. Given the following circuit find:

a) IA

b) IB

c) ILINE

insert diagram here

Ans: P8 V2

39. For the parallel circuit illustrated calculate:

a) equivalent impedance

b) line current

c) power factor

d) power supplied to the circuit.

insert diagram here

Ans: P12 V1

40. Two inductive coils of resistance values 5 ohms and 8 ohms and inductance values 0.02 H and 0.01 H respecitvely are connected in parallel across a 240 V  50 Hz supply.  Find:

a) coil currents

b) the circuit current

c) the circuit power factor

41. How can the power factor be improved in an A.C. system? How would methods to improve the power factor effect the power consumed?

Ans: P78 V1

42. A 50 kW A.C. generator has a power factor of 0.7.  The power factor is raised to 0.8 with the same kVA, find the % increase in kW output.

Ans: P89 V1

43. For what purpose are transformers fitted in the electrical system of a ship?  The windings of a 10 kVA 2400 240 V 60 Hz transformer has resistances of 6 ohms and 0.06 ohms. If the total loss at full load is 268 watts, find the copper loss and the core loss at the condition stated.

Ans: P60 V1

44. Sketch the open circuit test on a transformer clearly showing all the instruments.  The following readings were taken on a 400 to 220 V transformer on the open circuit test.

Find:

a) the magnetising component of the no load current

b) iron loss component

c) the transformation ratio

45. Sketch and describe the construction of a current transformer.  What other salient features are incorporated to make the machine efficient?  Why must the secondary circuit of a current transformer never be opened when the primary is energized?

Ans: P64 V1

46. Sketch and describe  a linear voltage differential transformer. Give some applications of the L.V.D.T. slug.

47. Given the following data on a transformer, calculate the primary voltage and turns ratio.  Also calculate the primary and secondary current.

Data: secondary voltage 13200 V

primary turns 900

primary flux 1 x 10-3

output 440 kVA 60 Hz

Derive the formula used in this problem

Ans: P76 V1

48. Describe the construction of a transformer and what are it's functions?  A transformer has a primary winding of 800 turns and a secondary of 160 turns.  It is rated at 10 kVA at 480 V.  Find:

a) ratio of transformation

b) approximate primary voltage

c) rated full load secondary current

Ans: P46 V1

49. There is a method of connecting a transformer to obtain a two phase three wire secondary output from a three wire three phase input.  Sketch a diagram to show how this would be accomplished using the SCOTT TAP method.   Show the position of the tap in the sketch.

Ans: P38 V2

50. Three phase transformers may be connected in banks in the following manner:

a) delta delta

b) delta wye

c) wye wye

d) wye delta

Discuss the particular application each would be used for and state the advantages or disadvantages ensuing from such application.

Ans: P49 V1

51. Give the advantages of using ultra high voltages in the transmission of electric power between the source of generation and the load point.  A transformer with a rating of 2400 - 240 V has 2000 turns on the primary winding. Assuming a 3% voltage drop in the transformer when fully loaded, how many turns should be placed on the secondary to maintain its rated voltage at full load.  With this number of turns on the secondary and the primary voltage held constant, what is the secondary no-load voltage?

Ans: P51 V2

52. For the " no load " test on a transformer, the ammeter was found to read 0.18 A and the wattmeter 12 W.  The reading on the voltmeter was 400 V.  Calculate:

a) the magnetizing component of the " no load " current

b) the iron loss component

c) the transformation ratio

Ans: P51 V2

53. A three phase, marine dry type transformer is used to step down the voltage of a three phase, star connected alternator to provide the supply for 120 V lighting.  The transformer has a 4 : 1 phase turns ratio and is delta connected on the primary side and star connected on the

secondary side.  If the lighting is supplied at the line voltage of the transformer, what must be the phase voltage of the alternator.

54. Illustrate a 3 phase power supply utilizing 220 V for power purposes and 110 V for lighting.  If the loads are unbalanced sketch a system that will accommodate the unbalance.

Ans: P7 V2

55. A delta primary and star secondary transformer of 200 kVA capacity has a primary voltage of 6600 V  and secondary voltage of 440 V 3 phase.  If this transformer is loaded with a 110 kW motor that takes 440 V 60 Hz with a p.f. of 0.8 and an efficiency of 83%, find the phase current in the primary.

Ans: P88 V1

56. A 6 pole three phase 550 V 60 Hz induction motor has a 5% slip and draws a current of 30 A when delivering a shaft torque of 150 Nm.  Assume windage and friction losses amount to a torque of 10 Nm and the iron and copper loss at 900 W. Calculate:

a) motor speed

b) brake power

c) input power

d) power factor

e) efficiency

Ans: P10 V1

57. A 500 V three phase alternator supplies a balanced delta connected load in parallel with a balanced star connected load.  The delta load is 30 kW at a power factor of 0.92 (leading) The star load is 40 kW at a power factor of 0.85 (lagging).  Calculate the line current and the power factor of the supply.

Ans: P85 V1

58. A 3 phase 440 V 60 Hz six pole induction motor develops 18 kW on full load with a speed of 1164 R.P.M. and operating power factor of 0.88 (lagging).  Calculate the full load:

a) slip

b) input in kW

c) line current

note: the stator loss is 1.7 kW and mech losses total 1.5 kW

Ans: P29 V2

59. A 3 phase 6.6 kV 60 Hz alternator has an equivalent armature reactance of 5 ohms per phase and negligible resistance.  It is connected to bus bars which are energized by a second identical alternator.  The breaker is closed when both armatures are rotating at 1800 R.P.M. but 2 electrical degrees out of phase.

Calculate:

a) synchronizing current

b) synchronizing torque

Ans: P44 V1

60. An electrical system load consists of a 300 kW induction motor power factor 85% and 100 kW lighting load with power factor 100%.  It is proposed to increase the system power factor to 95% by employing a 100 kW synchronous motor.  Find:

a) the kVA of the synchronous motor

b) the power factor of the synchronous motor

Ans: P58 V1

61. A 440 V single phase motor is rated at 7.5 kW and operates at a power factor of 0.8 with an efficiency of 88%. Find the current taken from the supply.

62. A shunt generator delivers 50 kW at 250 V at 400 R.P.M. The armature and field resistances are 0.02 ohm and 50 ohms respectively.  Calculate the speed of the machine when running as a shunt motor taking 50 kW input at 250 V.  Allow 2 volts for brush contact drop.  Assume flux to be proportional to field current.

Ans: P63 V1

63. A fresh water pump is found to take an armature current of 25 A at 220 V when running on full load.  The speed is measured to be 725 R.P.M. and the armature resistance is 0.2 ohm.  If the field strength is reduced by 10% by means of the speed regulator and the torque remains unchanged, determine the steady speed ultimately attained and the armature current.

Ans: P77 V1

64. Find the generated e.m.f. per conductor of a 6 pole D.C. generator having a magnetic flux per pole of 64 mWb and a speed of 1000 R.P.M..  If there are 468 conductors, connected in six parallel circuits, calculate the total generated e.m.f. of the machine.  Find also the total power developed by the armature when the current in each conductor is 50 A.

Ans: P88 V1

65. A six pole three phase generator generates 200 V 60 Hz with a field current of 4 Amps.  If the speed is changed to 1400 R.P.M. and the field current to 3 A, determine the generated voltage.

66. A D.C. shunt motor is wave wound and has four poles.  The flux per pole is 2.5 x 10-2 weber.  Armature current is 200 A the supply voltage is 230 V.  Conductors = 294. Armature resistance = 0.35 ohm.  Calculate the R.P.M. and torque.

Ans: P9 V2

67. The curve of induced e.m.f. against excitation current for a separately excited generator when run on no load at 1200 R.P.M. is given by:

e.m.f.     15    88   146   196   226   244   254

Excitation  0   0.4   0.8   1.2   1.6   2.0   2.4

current

Deduce the voltage to which the machine would self-excite if the shunt field resistance was set at 90 ohms and the machine was run at 900 R.P.M.

Ans: P41 V2

68. A pump delivers 12700 liters per hour of water into a boiler working at 15 bars.  The pump is 82% efficient and is driven by a 220 V motor, having an efficiency of 89%. Calculate the current taken by motor.

note: 1 liter of water = 1 kg

note: 1 bar = 105 N/m2

Ans: P22 V2

69. A shunt motor operates at 1200 R.P.M. and the supply voltage is 220 V.  The current is 60 A and the shunt field resistance is 110 ohms.  The armature resistance is 0.15 ohms.  What percent variation in speed will there be if the torque is reduced to 50%.

Ans P27 V1

70. A compound wound long shunt D.C. motor has an output of 150 A at 220 V.  The equivalent resistances of the armature, series and shunt fields are 0.025, 0.015 and 176 ohms respectively.  There is a 2 volt drop across the brushes. Find the induced voltage.

Ans: P45 V1

71. A 460 V D.C. motor takes an armature current of 10 A at no load.  At full load the Ia is 300 A.  If the resistance of the armature (Ra) is 0.025 ohm, what is the value of the back e.m.f. at "no load" and "full load".

Ans: P65 V2

72. Determine the resistance of each step of a starter for the following motors:

10 h.p. 240 V armature resistance 0.5 ohm and full load current limited to 45 amps.

note: the starting current to be 150% of full load current

Ans: P66 V2

73. Illustrate the construction of an induction motor. Describe how it operates and explain the difference between it and a synchronous motor.

Ans: P90 V1

74. Discuss the difference between synchronous motor and induction motor.  How is a synchronous motor started?

Ans: P82 V1

75. What is the theory of operation of an A.C. synchronous motor?  Why is there no starting torque?  In an 8 pole synchronous motor what would the speed of rotation be at:

a) 60 Hz

b) 50 Hz

76. Discuss the functions of the following elements of an automatic voltage regulator for an alternator:

a) error detecting element

b) correcting element

c) stabilizing element

Ans: P19 V1

77. Discuss a synchronous motor.  State two main functions of the damper winding.

Ans: P82 V1

78. Sketch and describe a motor controll starter for a synchronous motor.  How are: overload, winding damper, breaker incorporated into the circuit.

79. Explain what a damper winding is.  Sketch it and where would you find them.  A three phase 3.3 kV  50 Hz alternator having an equivalent armature reactance of 5 ohm per phase and negligible resistance is connected to bussbars to which an identical alternator is already connected.  The circuit breaker was closed at an instant when the rotors of the two machines were running at 1500 R.P.M. but out of phase by 1 mechanical degree.  Calculate:

a) the synchronizing current

b) the synchronising torque at this instant

80. Describe frequency as pertinent to A.C..  A four pole A.C.  generator runs at 1500 R.P.M., what is it's frequency?  If this generator supplies current to a 40 pole motor, find the

speed of the motor:

a) if it is synchronous

b) if it is induction with slip of 2%

Ans: P52 V2

81. A six pole three phase 50 Hz induction motor is running at full load with a slip of 4%.  The rotor is star connected and it's resistance and standstill reactance are 0.25 ohm and 1.5 ohm respectively.  The e.m.f. between the slip rings at standstill is 100 V.  Find the full load conditions:

a) the e.m.f. induced in each rotor phase

b) the rotor impedance per phase

c) the rotor current and p.f. assuming the slip rings are short circuited

Ans: P65 V2

82. A six pole three phase 60 Hz induction motor running at full load has a 4% slip.  The rotor is star connected.  Rotor resistance is 0.25 ohms per phase.  Standstill rotor  reactance is 1.5 ohms per phase.  Standstill e.m.f. on the slip rings is 100 V. Calculate:

a) the e.m.f. induced in each rotor phase

b) rotor impedance per phase

c) rotor current and power factor with shorted slip rings

83. Find the line current for a 440 V 3 phase motor which is 88% efficient and is rated at 110 kW.  The current lags the voltage by 30 degrees.

Ans: P19.2 V2

84. A four pole alternator on open circuit generates 200 V at 50 Hz when it's field current is 4 A.  Determine the generated e.m.f. at a speed of 1200 R.P.M. and a field current of 3 A neglecting saturation of the iron parts.

Ans: P25 V2

85. The terminal voltage of a shunt wound generator is 150 volts and the current output is 70 amperes.  If the resistance of the field windings is 30 ohms and that of the armature conductors is 0.06 ohm, calculate the electrical efficiency of the generator.

Ans: P26 V1

86. Sketch and describe a three phase alternator.  Explain how to connect up two alternators in parallel, in particular state the procedure for synchronizing.

Ans: P31 V1

87. Sketch and describe an A.C. alternator.  How is the alternator excited?

88. An 8 pole alternator running at 720 R.P.M. supplies current to a synchronous motor with 48 poles.  Calculate the frequency and speed of rotation of the motor.

Ans: P35 V1

89. A three phase 100 R.P.M. A.C. generator supplies a 50 Hz current to a three-phase, 120 R.P.M. synchronous motor. Calculate the number of poles on both the alternator and motor.

90. A 440 V three phase eight pole marine alternator generates a 50 Hz supply when dirven at normal speed.  If the system is to be converted to 60 Hz working, find the speed at which the prime-mover is to run.  Assuming the same excitation value find the new system voltage

91. What causes overheating in a squirrel cage motor? Discuss the preventive maintenance required on this type of motor.

Ans: P91 V1

92. Discuss the reasons for an induction motor overheating. Discuss preventive maintenance which whould be carried out on induction motors.  How would you reverse the direction of an induction motor?

93. Define: (as applied to D.C. starters)

a) current limit

b) time limit acceleration Sketch the diagram for one of the above types for a 1.5 kW wound motor.

Ans: P91 V1

94. Describe a magnetic motor starter for an A.C. three phase, two speed motor (full voltage).  Illustrate the answer with a simple circuit diagram.  Show the protection devices, control station, contactors and coils.

Ans: P19.1 V2

95. A D.C. starter is used for a shunt wound motor utilizing 230 V.  If the armature resistance is 0.6 ohm and the maximum permissible is 50 amperes and minimum at 40 amperes.  Find the first resistance.

Ans: P89 V1

96.  a) Describe an "air circuit breaker" .

b) Sketch and describe an "arc chute".

c) Define "reverse power relay"

Ans: P19.2 V2

97. Define each of the following terms as related to an A.C . motor starter enclosure. Define:

a) "disconnect"

b) "Short circuit protection"

d) "Start / Stop control"

Draw a simple diagram of a 3 phase A.C. motor starting circuit which embodies these features

Ans: P42&43 V2

98. Sketch a D.C. shunt motor Automatic Starter showing all protection devices, etc. It should incorporate a time limit acceleration application. Explain it's operation.

Ans: P19.1 V2

99. Describe the functions of a D.C. motor manual drum controller,illustrate your answer with a simple circuit diagram.

Ans: P54&55 V1

100. Describe a circuit breaker as fitted on the electrical switchboard in the engine room of a ship, and explain how it functions. Illustrate your answer with a sketch.

Ans: P16 V2

101. Draw a simple circuit diagram for a 3 phase A.C. motor incorporating the following

a) "motor delta wound"

c) " short circuit protection"

d) "disconnect"

e) "reversing"

f) "magnetic contactors"

g) "push button stn."

h) "Indicator lamps"

State the frequency of operation when Fwd. and Rev. buttons are pushed. What protection is provided against the possibility of pushing the Fwd. and Rev. buttons at the same time?

Ans: P77a V1

102. Describe an "air circuit breaker" suitable for 600 V A.C.  installation. Sketch some type of "arc chute" with the above breaker and explain how it functions to dissipate the arc.

Ans: P42 V1

103. Describe the functions of a D.C. motor manual drum controller: Illustrate your answer with a simple circuit diagram. A 25000 ohms voltmeter and a 35000 omhs voltmeter are connected in series across a 500 volt line. What will each meter indicate?

Ans: P54 V1

104. Describe a motor controller suitable for a synchronous system. Illustrate your answer with a simple circuit diagram and include an explanation of the starting sequence. Why are overload and damper winding protection fitted in the circuit.

Ans: P62 V1

105. Sketch and describe a 3 terminal rheostat type starter for a D.C. motor.

Ans: P84 V1

106. Describe  a starter that could be used for an A.C. motor application of full voltage, single speed, suitable for 750 W at 115 volt. Show in your sketch the protection devices, control station, contacts and hold in coil.

Ans.: P38 V2

107. Sketch and describe the operation of a two speed A.C. induction motor starter.  Your sketch is to include all safety and protective devices.  The line voltage is 440 V.

108. Describe and sketch a simple manual starter for a D.C. shunt motor and indicate why it is necessary to use this device to start the motor.

Ans: P22 V2

109. In the sketch shown, determine the resistance of each step of the starter for the following motor.

10 hp. at 240 volt with an armature resistance of .5 omh and full load current of 45 amps. Starter current to be 150% of the full load current.

insert diagram here

Ans: P66 V2

110. Describe and diagrammatically sketch a main switchboard for a vessel having three D.C. current generators. Indicate on your sketch all the necessary fittings, meters etc. and explain the purpose of each.

111. Assuming one generator is on load, describe the procedure necessary to bring the two machines on to the bussbar so that the three generators may run in parallel.

Ans: P37 V2

112. Sketch a D.C. switchboard suitable for paralleling two D.C. generators, show all instruments, switches and controls.

Ans: P37 V2

113. Sketch an A.C. switchboard suitable for paralleling two synchronous generators.  Your sketch is to show all protective devices and circuit breakers.  Find the line current supplied to a 12 kW motor which is 84% efficient at a power factor of 0.8 and 44 V.

114. Sketch and describe a main breaker.

115. Enumerate the advantage and disadvantages of a D.C. electrical installation (for lighting and auxiliary purposes) as compared with a similar A.C. system.  What instruments are required on the switchboard for each of these systems?  State the functions of the instruments named.

Ans: P28 V1

116. Discuss the starting sequence of an emergency generator which starts, automatically, in the event of a main power failure.

Ans: P81 V1

P17 V2

117. Make a sketch of a ships switchboard suitable for paralleling two or more D.C. generators. What is the reverse current relay and the overload relay and why are they necessary? State the procedure for paralleling a D.C. generator.

Ans: P37 V1

118. Describe with sketch a balancing arrangement for a 3 wire Edison system to provide 110 lighting and 220 volt power.

Ans: P70 V1

119. Detail a method of converting the measurement of the level of a liquid in a tank and the RPM. of a shaft into an electrical signal for input into a data logger.

Ans P16 & 17 V1

120. Using a sketch to illustrate and amplify your answer describe any one of the types of frequency meters listed below:

1) vibrating reed type

2) moving disk type of frequency meter

3) electrodynamic type

Ans: P31 V2

121 Describe the "megger". How is it used in testing circuits and equipment.

Ans: P38 V1

122. Describe an electric propulsion system employing a turbine driven alternator and D.C. propulsion motor. Use a sketch to help illustrate your answer. Why is the propulsion system made more complicated by employing A.C. and D.C. rather than the use of only one or other of these power modes. What type of rectification arrangements would likely be used in such a system.

There is a physical limit to the max. power available as output for which a direct current motor can be built. How does the designer overcome this restriction if much greater power per shaft is desired.

Ans: P30 & 31 V2

123. A boiler turbine generates electrical power in an industrial situation.  It operates at 15000 kPa and 520oC. Make a block diagram showing a closed loop for control of the system showing any safety devices.  Give a general description of any electronic or other devices used in this control system.

124. A steam turbine is used to generate power on a vessel. Sketch a block diagram of the control circuit showing the alarms, shutdowns and other safety devices.

125. More questions like these can be found on Martin's Marine Engineering Page, click to www.dieselduck.net.

125. Describe a typical impressed cathodic protection system used in a ship. What are the values of current and voltage used? What problem may be encountered if a current appreciably higher than recommended by the equipment supplier is applied.

Ans: P73,74,75 V1

126. Describe the construction of a semi-conductor rectifier indicating the materials used. Sketch the output wave of the bridge rectifier illustrated If a capacitor was connected across the output terminals, what effect will it have on the waveform?

insert diagram here

Ans: P15 V1

128. Describe the following:

a) semi-conductor

b) valence

c) hole

d) ion

e) forward bias

f) reverse bias

g) "p" type material

h) "n" type material

i) majority carriers

129. Discuss the precautions required when electrical equipment is to be used in flammable atmospheres. What is meant by the terms:

1) intrinsically safe circuits

2) flame proof apparatus

Ans: P21 V1

130. Describe an emergency lighting system which uses batteries. What care and maintenance does this system require? How are the batteries charged when the available power is A.C. Make a line diagram of such a circuit.

Ans: P61 V1

131. The circuit illustrated is that of a typical common-emitter amplifier. If the current through the emitter resistor is .5 mA, determine the battery voltage. Assume a base emitter voltage drop of .1 volt.

insert diagram here

Ans: P14 V1

132. Describe any emergency power installation fitted aboard ship. State the circuits this generator feeds and list the various connections on the switchboard of this installation.

Ans: P28 & 81 V1

133. Sketch and describe an emergency switch board for a large passenger vessel.

134. Sketch and describe a photo electric cell or  ? tube. Give two uses on a boiler

135. Sketch a fluorescent tube.  Describe how it produces visible light.  What is a ballast?

136. Given the following equation:

[ Eo =             1            C2  ] [ uo = 4 pi x 10-7  Wb]

4 pi x 8.98776 x 109    Nm2                        Am

a) Show that the correlation between both of these quantities is numerically equivalent to the velocity of light.

b) Using dimensional analysis show that the units required for "C" are consistant with the formulae in part "a".

137. What are damping bars and why are they fitted to A.C. generators and synchronous motors.