QUESTION BANK MARINE ELECTRICAL TECHNOLOGY PART-3

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

a) Rectifier circuit

b) Amplifier circuit

c) Oscillator circuit.

Q List at least two 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?

Q It is proposed to operate a bow thruster unit from a 3.3 kV electrical supply. Outline appropriate option for the design of installation under each of the following

a) Prevention of the main switchboard

b) Overload of bow thruster motor

c) Cable protection

Q Differentiate between half and full wave rectification. State where half wave rectification may be used & the purpose for which it is not well adapted. Draw a bridge connection by which full wave rectification may be obtained.

Q Explain the meaning of “p” & “n” type semi-conductor materials & give a brief description of the mechanism by which current passes through them.

Q a) What is “open loop” & “close loop”? Discuss the relative advantage of each.

b) Draw a practical close loop system & describe the loop explaining the meaning of the terms:

i. Servo motor

ii. Feedback

iii. Sensor element

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

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

i. Peak load current

ii. DC load current

iii. AC load current.

Q a) What is reactive power? Why is such a term not encountered when D.C. sources are used in electric circuit?

b) A transistor amplifier stage consists of a transistor of parameters hie =800Ω hfe = 50 & hoe = 20μS, & bias components & coupling capacitors of negligible effect. The input signal consist of an e.m.f. of 60 mV from a source of internal resistance 2.2 kΩ, & the total load on the stage output is 4 kΩ. Determine the current, voltage & power gains of the amplifier stage.

Q Evaluate for a frequency of 15 kHz, the amplification and the phase difference between input & output signals of a voltage amplifier using a triode having an amplification factor of 48 & a mutual conductance of 1.2 m A/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 & the total shunt capacitance is 90 μF.

Q With reference to the electronic control systems:

a) Draw a simple block diagram for the temperature control

b) Describe each component  that is shown in the diagram in (a)

Q With reference to U.M.S. operations:

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

b) As 2/E, describe how you would respond to the irretrievable failure of the Machinery space fire alarm system whilst the ship is on the voyage.

Q With reference to the condition monitoring of the electrical machinery:

a) State 2 important parameters that may be recorded.

b) Explain how the parameters are measured & what defects may be revealed.

Q Explain what is meant by & the significance of, four of the following terms.

a) Voltage Stabilization

b) Filter choke

c) Impedance

d) Rectification

e) Grid bias voltage

Q a) i. Discuss the various hazards & problems which are associated with electric cable Insulation in the event of fire.

ii. Suggest remedies for these problems

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

Q Describe:-

a) A safety lamp approved as part of the slips statutory equipment

b) A self-igniting lamp suitable for the attachment to a lifebuoy.

State the attention required to maintain them in a satisfactory working condition.

Q a) What is intrinsic electric safety?

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

c) Describe intrinsically safe equipment used on board the ship?

Q Discuss the suitability and limitations of the following insulating materials for use on board ships & state suitable application in each case. Particular reference should be made to the influence of the environment & its effect on deterioration in service:

a) Pure rubber

b) Paper

c) Mica

d) Porcelain

e) Ebonite

Q Differentiate series and parallel resonance. Draw impedance characteristics of these circuits.

Q a) Sketch an arrangement showing the principal of a proportional plus integral (P-I) control loop?

b) What is meant by negative and positive feed backs? Explain the characteristic of negative feedback.

c) Compare the series and parallel resonance circuits. Find the frequency at which the following circuit resonates.

Q a) A series circuit having resistance, inductance and capacitance is to be operated on a constant voltage supply of available frequency. Indicate graphically how change takes place in the current & voltage in resistance, inductance & capacitance, & also capacitance reactance & inductive reactance.

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

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

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 100V, 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.

Q Draw the circuits of resistive and capacitive voltage drivers. What are the differences between them? For the following circuit, what is the voltage across C2.

Q a) On what factors does the capacitance of a parallel-plate capacitor depend?

b) A tuned circuit consisting of a coil having an inductance of 200 μH and a resistance of 20 Ω in parallel with a variable capacitor is connected in series with a resistor of 8000 Ω across a 60 V supply having a frequency of 1 MHz. Calculate:

i. The value of C to give resonance

ii. The dynamic impedance and the Q factor of the tuned circuit

iii. The current in each branch

Q a) i. What is direct connected alternator?

ii. How is direct connected exciter arranged in an alternator?

b) Find the synchronous impedance & reactance of an alternator in which a given field current produces an armature current of 200 A on short circuit & 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 lagging, with a terminal voltage of 200 V.

Q a) i. What is direct connected alternator?

ii. How is direct connected exciter arranged in an alternator?

b) Find the synchronous impedance an 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

Q a) Define following terms with reference to alternating currents

i. Cycle

ii. Time-period

iii. Frequency

iv. Peak factor

b) A heater unit of inductance has a resistance of 6.5 ohms and is intended for use with 100 V mains. For what 50 Hz voltage would it be suitable when placed in series with an external apparatus, of negligible resistance, having an inductance of 0.01H. If the frequency rises by 5 % and this voltage remains constant, watt constant, what would be the resulting change or voltage at the heater terminals?

Q A resistor of ohm value 3 ohms is connected in series with a coil of inductance 0.1 H and resistance 1 ohm. If 100 V at a frequency of 50 Hz is applied to the circuit, find the current flowing.

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

b) Three impedances Z = 5 + j4 are connected in the form of a delta to three loads of a balanced 3- phase circuit. The line voltage is 120 volts. Find:

i. The phase current

ii. Power factor

iii. The volt-ampere in the circuit