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09/7/2010.

INDEX

MARINE ELECTROTECHNOLOGY.

Question

Tank liquid sensors are an integral part of the ship

Describe with the aid of suitable sketches the working principle of cap activity type level sensor

Ultra level sensor

Float.

Question

With reference to dynamic positioning system what do you understand by the term redundancy?

With the aid of a simple block diagram explain the difference between [dynamic positioning] DP 1, DP 2, And DP3. Enumerating their relative advantages and disadvantages.

Question Sr. No: 12 (2012) Sr. No: 1 (2013)

What is soft starting of an induction motor

Describe with a circuit using thyristor used for soft starting

Discuss its advantages and disadvantages.

Question

	Sr. No: 1 (2010)	Sr. No: 2 (2010)	Sr. No: 2 (2011)	Sr. No: 8 (2011)
Sr. No: 6 (2013)	Sr. No: 2 (2014)	Sr. No: 8 (2014)

Explain how the efficiency and regulation of a transformer can be assessed by open and short circuit tests.

What is meant by equivalent resistance?

Question

	Sr. No: 1 (2010)	Sr. No: 2 (2010)	Sr. No: 2 (2011)	Sr. No: 9 (2010)
Sr. No: 6 (2011)	Sr. No: 8 (2011)	Sr. No: 11 (2012)	Sr. No: 2 (2014)	Sr. No: 8 (2014)

Compare methods of obtaining speed regulation of 3 phase induction motors generally used in tankers by means of rotor resistance. Cascade system. Pole changing. Give examples where each system may be employed with advantages.

Question

	Sr. No: 10 (2011)	Sr. No: 3 (2012)	Sr. No: 4 (2012)	Sr. No: 12 (2012)
Sr. No: 7 (2013)	Sr. No: 12 (2013)

Explain the effect of reduced voltage on standard squirrel cage motor with respect to each of the following.

Burn out.

Starting current.

Starting torque.

Speed.

Question Sr. No: 10 (2011) Sr. No: 12 (2012)

Describe with the aid of a simple sketch the arrangement of the 3 phase winding of an alternator showing the neutral point.

Explain why for most ship the neutral is insulated.

Explain why in some installation the neutral point is earthed.

Question

	Sr. No: 1 (2010)	Sr. No: 2 (2010)	Sr. No: 2 (2011)	Sr. No: 8 (2011)
Sr. No: 11 (2012)	Sr. No: 2 (2014)	Sr. No: 8 (2014)

Give a brief outline of the care and maintenance that should be given to the stator and rotor of an AC generator.

State what is likely to occur if the driving power of an ac generator suddenly fails when 2 generator are operating in parallel.

Question

Quest: 3	Sr. No: 1 (2010)	Sr. No: 2 (2010)	Sr. No: 2 (2011)	Sr. No: 9 (2010)
Sr. No: 6 (2011)	Sr. No: 8 (2011)	Sr. No: 7 (2012)	Sr. No: 11 (2012)	Sr. No: 1 (2014)
Sr. No: 8 (2014)

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.

Question

	Sr. No: 1 (2010)	Sr. No: 2 (2010)	Sr. No: 2 (2011)	Sr. No: 9 (2010)
Sr. No: 6 (2011)	Sr. No: 8 (2011)	Sr. No: 11 (2012)	Sr. No: 2 (2014)	Sr. No: 8 (2014)

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

Sketch a circuit diagram for a pole change motor

Describe how speed change and braking are achieved

Question

	Sr. No: 6 (2010)	Sr. No: 7 (2010)	Sr. No: 11 (2010)	Sr. No: 7 (2011)
Sr. No: 11 (2011)	Sr. No: 1 (2012)	Sr. No: 4 (2013)	Sr. No: 12 (2013)

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 the, operation of this power trip is based and how tripping is activated.

Question Sr. No: 1 (2012) Sr. No: 4 (2013)

Describe W.T.A. Of Sketch the operation of a synchroscope

State the information obtained from it

Suggest a substitute in the event of sychroscope and stand by light failure

Question

Differentiate with the aid of simple sketches between 2 of the following type of electronic circuit.

Rectifier circuit. Amplifier circuit. Oscillate circuit.

Question Sr. No: 1 (2012) Sr. No: 4 (2013)

Sketch 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.

Question Sr. No: 10 (2011)

Sketch a diagrammatic arrangement of a static or self excited alternator.

Describe the operation of the self excited alternator.

State why the voltage dip is less in a self excited alternator than in brushless or conventional alternator

Question Sr. No: 10 (2011)

What is intrinsic electric safety?

Can live maintenance be done on intrinsically safe circuit?

Describe intrinsically safe equipment used on board ship.

Question

With particular reference to high voltage electrical system explain the permit to work

State with reasons the item that should be included in a work permit for maintenance on a high voltage switchboard.

Question

With reference to fluorescent lamps.

Describe a switch type starter.

Describe a transformer quick start.

List two reasons for inclusion of capacitor to fluorescent light circuit.

Question

Explain meaning with reference to electrical safety equipment.

Intrinsically safe

Flame proof

Increased safety.

Pressurised equipment

Sketch a safety barrier for intrinsically safe circuit & state it purpose.

Question

Describe the requirement of each of the following electrical equipment.

A shore to ship supply of alternating current.

Portable lighting for inspection of duct keel space.

Question

With reference to fire detection unit

Describe a rate of heat rise detector with the aid of a sketch.

Describe the following methods of checking the integrity of a suction of fire detection heads

Loop monitoring.

Line termination monitoring.

Question

With respect to personal carrying out inspection and maintenance involving entry to boiler and other confined spaces

State the precaution needed for the operation of portable electrical tools and lighting with respect to safety.

Outline the routine checks carried out on the equipment.

Question

With reference to hull cathodic protection system of impressed current types

Sketch and describe such a system.

Explain how protection may be ensured for the rudder and propeller.

State any precaution that should be taken when this type of system is installed.

Question

Describe a alkaline battery cell listing the material used in its manufacture

With reference to alkaline batteries used on ship

Sate each of the following.

Significance of the relative density reading of electrolyte.

When the electrolyte would normally be renewed

Reason why the voltage reading of this type of battery is not necessarily indicative of its condition.

The normal temperature range and safe temperature limit of battery

Effects of low and high temperature.

Question

Quest: 1	Sr. No: 6 (2010)	Sr. No: 7 (2010)	Sr. No: 11 (2010)	Sr. No: 7 (2011)
Sr. No: 11 (2011)	Sr. No: 11 (2013)

With the aid of sketch describe the main features and 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:

(i) As an ammeter to read up to 150 A.

(ii) As a voltmeter to read up to 150 V.

No calculations are required.

Question

Quest: 2	Sr. No: 3 (2010)	Sr. No: 6 (2010)	Sr. No: 7 (2010)	Sr. No: 11 (2010)
Sr. No: 7 (2011)	Sr. No: 11 (2011)	Sr. No: 12 (2011)	Sr. No: 11 (2013)

Describe a brush less alternator with a.c. exciter and static-A. V.R.

State the output voltage characteristics for this type of machine.

Question.

Quest: 2	Sr. No: 4 (2010)	Sr. No: 6 (2010)	Sr. No: 7 (2010)	Sr. No: 9 (2010)
Sr. No: 11 (2010)	Sr. No: 7 (2011)	Sr. No: 11 (2011)	Sr. No: 4 (2012)	Sr. No: 8 (2012)
Sr. No: 2 (2013)	Sr. No: 7 (2013)	Sr. No: 11 (2013)	Sr. No: 12 (2013)	Sr. No: 6 (2014)

With reference to U.M.S. operation.

State with reason the essential requirement for U.M.S.

As 2nd engineer describe how you would respond to the irretrievable failure of the machinery space fire alarm system whilst the ship is on voyage.

Question

Quest: 4	Sr. No: 6 (2010)	Sr. No: 7 (2010)	Sr. No: 11 (2010)	Sr. No: 7 (2011)
Sr. No: 9 (2011)	Sr. No: 11 (2011)	Sr. No: 1 (2013)	Sr. No: 11 (2013)

With reference to preferential tripping in a marine electrical distribution system.

(b) State why this facility is required.

(c) With the aid of a sketch, describe a typical arrangement to provide three stages of tripping as an instantaneous protection against short circuit.

Question

With reference to the protection of electrical power circuit

Explain the term discrimination and describe how it is achieved

Question Sr. No: 10 (2010)

Discuss the suitability and limitation of the following insulating material for use on board ships and state suitable application in each case.

Pure rubeer

Paper.

Mica.

Porcelain.

Ebonite.

Question

Describe

A safety lamp approved as part of ships statutory equipment

LIFEBUOY SELF-IGNITING LIGHTS

Question Sr. No: 10 (2010)

Why upon heavy impact loading self excited compounded alternator provide the best response in limiting voltage dip and recovery time.

Question

With reference to high voltage electrical distribution system

Sketch and describe a panel mounted earth fault monitor

Explain how HV system may be earthed.

Question

Describe the devices used to protect a 3 phase a.c. induction motor against the following faults.

Short circuit

Overload

Single phase fault.

Explain in contest of 1 & 2 why discrimination is necessary.

Question

Sketch and describe a Ward Leonard speed control method

Give 2 examples where Ward Leonard speed control method may be employed for ship board operation.

Question

Sketch a diesel electric propulsion arrangement for a ship

Describe the operation

Outlining how reversal of the propulsion motor is achieved.

Question

Quest: 1	Sr. No: 8 (2010)	Sr. No: 10 (2010)	Sr. No: 1 (2011)	Sr. No: 3 (2011)
Sr. No: 4 (2011)	Sr. No: 6 (2012)	Sr. No: 9 (2012)	Sr. No: 6 (2013)	Sr. No: 8 (2013)
Sr. No: 9 (2013)	Sr. No: 10 (2013)	Sr. No: 3 (2014)	Sr. No: 4 (2014)	Sr. No: 9 (2014)

The direct on line 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;

(b) Low starting torque.

Question

Sketch a main engine shaft driven generator with electronic system for frequency correction

Describe the operation of the generator arrangement sketched.

Question

With reference to squirrel cage, induction, electric motors:

(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 retro-fitted device used to improve the part load performance of an induction motor.

Question

With reference to time lag in the operation of over current protection devices

Describe 2 methods of obtaining time lag

Explain the purpose of time lag.

Explain discrimination with respect to electrical distribution system.

Explain inverse current time characteristic

Question

Immediate and subsequent action on stator high temperature alarm.

State the feature of the winding cooler tubes that prevent damage to the winding in event of a leakage.

Question

With reference to the operation of governors fitted to diesel alternators that generally operate in parallel:

Explain why an isochronous characteristic is undesirable;

State what is meant by droop and give an analogy of droop in control engineering terms;

Sketch a load/frequency diagram showing how two generators share the electrical load.

Question

Describe how the AVR monitors out put and controls the excitation system

Sketch a circuit diagram for AVR and how AVR utilize a silicon controlled rectifier to control the excitation system for an alternator.

Question

With reference to the paralleling of alternators:

Outline the principles of synchronisation;

Explain how KW power and KVAr are shared;

for two machines operating in parallel explain the consequences of EACH of the following faults;

(i) Failure of the excitation unit of one machine;

(ii) Sudden shutdown of one machine due to, steam or fuel supply, shortage.

Question

With reference to the parallel operation of electrical generators:

(a) Explain how two alternators may be synchronised;

(b) State how two alternator may be synchronised if the synchroscope is defective;

(c) Explain how synchronisation may be performed without any switchboard instrumentation;

(d) Explain the likely consequences if the timing of synchronisation is ineptly executed.

Question

It is proposed to operate a bow thrusters unit from a 3.3 KV electrical supply outline suitable option for the design of installation under each of the following heading.

Protection of main switch board

Overload of a bow thrusters motor

Cable protection.

Question

Describe, with the aid of a diagram, the operation of the following components of electrical equipment and explain the purpose of EACH:

Under voltage protection;

Miniature circuit breakers.

Question

With reference to voltage variation profiles caused by load changes imposed on alternating current generators:

(a) Sketch a voltage dip, showing an acceptable recovery time;

(b) Outline the salient factors that cause the variation in Q.

(c) Outline the salient factors of recovery from the variation in Q.

Question

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.

An insulated system is one that is electrically insulated from earth.

Question

With reference to the provision, of a shore electrical supply to a ship:

(a) Sketch an arrangement for taking A.C. shore supply and 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.

Question

In a A.C. generator voltage dip occurs in 2 stages

Sketch a voltage time graph showing the pattern of voltage dip

Referring to this graph state with reason the effect on the electrical system of a small power installation when large load is suddenly switched on.

Explain each of the following categories of voltage control.

Error operated.

Functional.

Question

With reference to electronic control systems:

(a) Draw a simple block diagram for temperature control;

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

Question

With reference to 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 the emergency installation can be periodically tested.

Question

Diesel 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.

Question

With ref to error actuated, automatic voltage regulators (AVR's) fitted to alternating current generators:

State the purpose of the A.V.R.;

With the did of a diagram, show an acceptable recovery pattern from the initiation of a voltage change;

In control parlance explain these elements that allow for

(i) Stability;
(ii) load change;
(iii) fast response.

Question

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

Describe the type of cumulative damage that may be caused when alternators are incorrectly Synchronized.

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

For two alternators operating in parallel the consequences of:

Reduced torque from the prime mover of one machine.

Reduced excitation on one machine.

Question

(a) Explain the advantages and disadvantages of fitting shaft driven generators.

(b) Outline FOUR methods of installation for shaft generators.

Question

State the problem that would occur if large induction motor such as bow thruster unit were started direct on line.

Outline 6 proactive design methods that may be employed to eliminate problem that occur during starting of large induction motor.

Question

Sketch the lay out of a solid state soft starter motor for a bow thruster unit powered from a dedicated diesel alternator.

Outline the advantages of the system sketched in relation to systems deriving power from the main switch board and from dedicated diesel alternator without soft starter motor.

Question

With reference to deck machinery driven by A.C induction motor describe each of the following types of braking.

Regenerative. Plugging. Dynamic.

Question

Describe how starting torque of electric induction motor may be improved by using each of the following.

Wound rotor motor

Double cage motor.

Question

With reference to the protection of electric motor explain each of the following.

Fuse back up protection.

How a motor fitted with fuse back up protection may exceed its rated temperature without being tripped by its primary protection

A means of protection for a motor to safeguard the rated temperature being exceeded.

Question

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.

Question

(a.) Describe the protection incorporated in AC. electrical switchboards.

(b) State with reasons what maintenance is required for switchboards and associated equipment.

Question.

Discuss the various hazards and problem which are associated with electric cable insulation in the event of fire.

Suggest remedies for these problems.

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

Question

Quest: 4	Sr. No: 6 (2012)	Sr. No: 7 (2012)	Sr. No: 6 (2013)	Sr. No: 8 (2013)
Sr. No: 9 (2013)	Sr. No: 1 (2014)

Differentiate between squirrel cage and wound rotor motor of the three phase a.c. induction.

In respect of the following

Rotor construction, torque characteristic, speed variation.

Question

a) State the necessary operations for paralleling an A.C. generator;

b) With the aid of a sketch, show how the emergency synchronizing lamps are connected;

Question

Describe, with the aid of a sketch, an instrument type earth leakage detector.

State why an instrument type detector may be fitted in preference to simple earth lamps

Question

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

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

Give a safe procedure to follow should a main circuit breaker fails to open under fault condition.

Question Sr. No: 8 (2012) Sr. No: 2 (2013)

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

(a) State the reasons for this.

(b) Sketch a starling system that may be useful for such motors.

(c) Describe the starting method sketched in (a, b ).

Question

Why is it important to maintain high efficiency, of operation and low values of voltage regulation for power transformers?

Question

What is direct-connected alternator?

How is a direct-connected exciter arranged in an alternator ?

Question

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

Question

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?

Question

Explain the working principle of a 3phase, induction motor. What are the various types of rotors?

Question

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.

Root-Mean-Square (R.M.S.) Value

Question

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

Question

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?

Question

a) Sketch the circuit diagram of an instrument for testing insulation resistance.

b) State the precautions to be observed when using the instrument described above.

Question

a) Sketch the circuit diagram of an instrument used for measuring electrical insulation resistance.

b) Describe the circuit diagram sketched, explaining how it operates when measuring electrical insulation resistance.

Question

a) Sketch a diagram of an automatic voltage regulator of the zenor bridge type used in the control unit of a 3 phase ac generator.

b) Describe how the regulator  sketched operates, making particular reference to the operation of the zenor diodes.

Question

a) With reference to single phasing applied to a.c motors

i) Explain the meaning of single phasing

ii) Describe it's effect

iii) State the most common cause of single phasing.

b) Sketch a simple diagram of a direct on line starter, showing in detail, the overload and single phase Protection trip.

Question

Describe the effects of frequency and voltage change on an induction motor.

Question.

With reference/to the insulation testing of marine electrical plant:

State the reason for insulation testing;

State the precautions to be observed when testing intrinsically safe equipment Type Ex. I'

Describe the overhaul of a a.c.\ d.c. motor which has been subject to excessively damp condition or flooding with seawater.

Question

State how safety is achieved with regard to gas emission in battery rooms where a large number of lead-acid cells are stored with reference to:

(a) Provision of lighting;

(b) Ventilation if a fan is fitted,

(c) Type of distilled water container for topping up;

(d) Use of tools and replacement of defective batteries

Question.

A cage rotor motor has been flooded with sea water, the insulation resistance can drop down to zero MΩ. describe the procedure for putting the motor back into service

Question.

What are routine maintenance carried out on an a.c. motor and

Explain the meaning of single phasing in a.c. machinery

State the dangers associated with single phasing & enumerate the protective devices normally fitted to counteract such dangers.

Question

What is the operational impedance of an R.C. Circuit? Describe its usefulness.

Question

What are the factors on which the speed of the motor depends. Discuss them for series and shunt.

Question

How do the leakage flux effect the operation of a transformer

How are they minimised

Question

Derive an expression for the e.m.f induced in a a.c. generator.

Question

What is back emf. Derive the relation for the back emf and the supplied voltage in terms of armature reactance.

Question

Describe the effect of the following loads on power factor :

(i) Induction motors.

(ii) Transformer.

(iii) Partly loaded motor.

(iv) Cage type motors.

Question

Explain what is meant by, and the significance of, any four of the following terms.

(a) Voltage stabilization.

(b) Filter choke.

(c) Impedance.

(d) Rectification.

(v) girid bias voltage.

Question

Explain the potential hazards if liquid-cooled transformers are used.

What are the losses in transformers? Mention the various factors which affect these losses.

Question

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

Question

Define the following terms with reference to alternating currents.

1) Cycle.

2) Time-period.

3) Frequency.

4) Peak factor.

Question

What is SHORT CIRCUIT and how may a short circuit develop

Question

Describe the action of a diode valve

Question

Explain the term CAPACITIVE REACTANCE

Question

What is INDUCTIVE REACTANCE?

Question

Why is a synchronous motor not self stating?

What are the various ways in which it can be started?

Question

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

Question

What is a commutator?

Question

Sketch a circuit diagram of a push button DOL contactor starter for 3phase incorporating overload and short circuit protection

Indicate on a sketch of typical characteristic curves of current and torque against speed, disadvantages of a DOL start squirrel cage induction motor.

Question

Explain how excitation of the rotor is produced and supplied.

Question

Explain the principle of AC motor starting and speed control

Question

Draw the complete phase diagram of the transformer under no load condition.

Question

Explain the term modulation

Question

Shunt generator having drooping characteristic are best suited for parallel operation

Question

Sketch and describe an arrangement for automatic connection of emergency batteries upon loss of main power.

Include in your answer:

Means of obtaining d.c. charging supply from a.c. mains;

A method of maintaining charge on lead acid batteries;

The arrangement to check that batteries operate at loss of main power

The length of time for which emergency batteries of passenger and cargo ships must provide power.

Question.

What are commutating (inter) poles? State purpose and location in DC generators and motors.

Why is squirrel-cage windings used on main propulsion motors?

Question

Sketch a lamp bright, lamp dark system configuration for synchronizing lamps

Question

a) Describe the principal of operation of each of the following detecting elements

i) Resistance thermometer

ii) Thermo - couples

iii) Thermisters

b) State one application for each of the detecting elements referred to above

Question

Explain the term RECTIFIER, HALF-WAVE RECTIFIER, FULL-WAVE RECTIFIER, BRIDGE RECTIFIER, Amplification Thermonic Emission:

Question.

What is open and close loop

Discuss the relative advantages

Sketch a practical close loop system and describe the loop explaining the term servomotor feed back sensor element

Question.

Describe the procedure for paralleling a 440-volt 3-phase AC generator with another generator on the line.

Question

What are the three basic types of ac motors? State their advantages, Disadvantages

Question

Describe the significance of h parameters

Draw the simplest transistor amplifier circuit and explain the function of each component

Question

What are the indications and causes of an overloaded generator?

Question

Mention and explain the various causes for the failure of the generator to build up.

Question

With the Aid of a sketch of delta and star connection diagram, state the basic equation from which the delta star, star delta conversion equation can be derived.

Question

Show how the power that is transferred across the air gap of a 3phase induction motor is represented explain the terms what portion of this is useful power.

Question

Distinguish between power efficiency and all day efficiency why is all day efficiency considered more reasonable basis for comparison than ordinary efficiency.

Question

Briefly describe the meaning of the expression star connected as applied to 3phase AC practice. What is the ratio of he maximum line voltage to the maximum phase voltage in each case.

Question

Describe the normal criteria used for setting thermal protection relays and their advantages compared to magnetic type.

Question

Describe the effect of change in speed, rotor current and torque as load is applied to an induction motor

How does the motor adjust to its stator current with changes in mechanical load?

Question.

Describe the situation in which hand regulation might be desirable for operation of generator when running.

Question.

Explain why the alternator output from phases are fed to separate bus bar.

Question.

Distinguish between Power and all day efficiency.

Question

Describe the material used as conductors in cable.

Question

What is meant by –ve feed and +ve feed back

Explain the characteristic of –ve feed back.

Question

What is slip?

What are the factors on which the torque of an induction motor depends?

Question

Describe the characteristics of a DC motor

Explain the advantages of such a DC motor for deck machinery

Describe with the aid of a sketch a control system for the motor in a

Question

List the factors that determine the maximum developed torque of the induction motor

Condition for maximum torque under running condition

Question

Describe with a sketch pneumatic relay and show how feed back can be achieved when such a relay is used in conjunction with a flapper mechanism.

Question.

Derive the relationship between anode resistance, mutual conductance, and amplification factor for a diode.

Question.

Describe the possible causes and effect of running a 3phase motor with one phase open circuited.

Question.

What are the characteristic of a PN junction diode, point out its specifications. Also point the significance of dynamic and static resistance.

CLICK TO OPEN SOME EXTRA QUESTION AND ANSWERS

PROBLEMS

Question

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.

Question

(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

Question

A 100 kVA transformer has 400 turns on the primary and 80 turns on the secondary. The primary and secondary resistances are 0.3 ohm and 0.01ohm respectively, and the corresponding leakage reactances are 1.1ohm and 0.035 ohm 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.

Question

The low voltage release of an AC motor starter consist 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 volt 50Hz AC supply the current taken at first is 2A, when plunger is drawn into the full in position, the current falls to 0.74

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.

Question

(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. The specifications of the batteries A, B and C are follows:

Battery A 105 V, Internal resistance 0.25 ohm

Battery B 100 V, „ „ „ 0.2 ohm

Battery C 95 V, „ „ „ 0.25 ohm

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

Question

A resistance of 130ohm. and a capacitor of 30 μf are connected in parallel across a 230 volt 50Hz supply.

Find the current in each component, total current, phase angle and the power consumed.

Question

An 18.65 KW, 6pole, 50 Hz, 3-phase slip-ring induction motor runs at 960 rpm on full load with t rotor current per phase of 35 A. Allowing 1 KW for mechanical losses, find the resistance/phase; of 3-phase rotor winding.

Question

A 12-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 3512 and inductive reactance 25ft. 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.

Question

A 230V motor, which normally develops l0 kW at 1000 rev/min with an efficiency of 85 per cent, is to be used as a generator. The armature resistance is 0.150 and the shunt-Held resistance is 2200. If it is driven at 1080 rev/min and the field current is adjusted to 1.1 A, 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?

Question

A coil having a resistance of 10 ohm and an inductance of 0.15 H is connected in series with e 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 ?

Question

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

Question

The earth-lamps on a main switchboard comprise two , 240V 60W lamps connected in the usual manner. The potential difference at the busbars is 220V. Damage by sea water occurs to a distribution cable so that the insulation resistance to earth is reduced to 16Ω and 6Ω for +ve and - ve cables respectively. Find by calculation (a) which of the two lamps burns the brighter; and (b) the additional load on the generators occasioned by the fault. The resistance of the cables and the ship's structure may be neglected, and that of" the lamps taken as constant at the value corresponding to the 60W rating.

Question

A coil of 0:84H inductance, and 50Ω resistance_: is connected in series with a capacitor of 14μ F capacitances " find the frequency for resonance and the potential differences across the capacitor, across the coil and across the two, when a current of 5A at this frequency, is flowing. (b) find the three potential differences when the same current flows at 60Hz.

Question

A three phase induction motor is wound for four poles and is supplied from a 5.0 Hz system.

Calculate.

(1) The synchronous speed;

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

(3)The motor frequency when the speed of the rotor is 600 r.p.min.

Question

In a 50-kVA, star-connected, 440-V, 3-phasc, 50-Bz alternator, the effective armature resistance is 0.25ohm per phase. The synchronous reactance is 3 2 ohm per phase and leakage reactance is 0,5 ohm per phase. Determine at rated load and unity power factor:

(a) Internal e.m f. E_a (b) no-load e.m.f En (c) percentage 'emulation on full-load (d) value of synchronous reactance which replaces armature reaction.

Question

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

Question

A 440V shunt motor takes an armature current of 30A at 700 rev/min. The armature resistance is 0.70. 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.

Question

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

Question

A section of supply cable AB 1km long has a fault to earth such that, when end B is disconnected, the resistance measurement from end A to earth is 5Ω . When end A is disconnected, the resistance reading from end B to earth is 3Ω . The length of the cable AB has a resistance of 4Ω when intact. Find the distance of the fault from end A.

Question

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 as current of 40A. Assume 60 percent reduction in flux for the 220 V connection.

Question

A. d.c. motor takes an armature current of 110 A at 480 V; The resistance of the armature circuit is 0.2H. The machine has six poles and the armature is lap-connected with 864 conductors. The flux per pole is 6.05 Wb. Calculate .

(i) The speed; (ii) The gross torque developed by the armature.

Question

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.

Question

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 (a peak load current, (b) DC load current, (c) AC load current.

Question

Three conductors fitted, side by side in the stator of a salient-pole alternator. Each generates .maximum voltage of 200V (sinusoidal). The angle subtended- at the ; Centre of the stat between, adjacent conductors is 20 electrical degrees. If the three conductors are connected series, find..'(a) the rms value of the effective voltage and (b)the breadth factor. Using the

theory that is the basis of this problem, give one; reason Why three phase current has be introduced.

Question

The following result were obtained on a 50KVA transformer

O.C test

Primary voltage = 3300V

Secondary voltage = 415V

Primary power = 430W

S.C test

Primary voltage = 124V

Secondary current = 15.34A

Primary power =525W

Calculate

The efficiency of full load and half load for 0.7pf

The voltage regulation for pf 0.7

1) Lagging

2) Leading

Question

The primary and secondary winding of a 500KVA transformer has resistance 0.42 and 0.0019ohm respectively

The primary and secondary voltage are 11000V and 415V respectively and the core loss is 2.9KW, pf = 0.8 calculate efficiency on full load and half load.

Question

A moving coil ammeter a thermal ammeter and a rectifier are connected in series with a resistor across a 110V ac supply

The circuit has a resistance of 50ohm to current in one direction and due to rectifier on infinite resistance to the current in infinite direction calculate

The reading on the ammeter

The form and peak factor of the current wave.

Question.

The no-load current of a transformer is 5.0 Amps, power factor 0.25, when supplied at

235 V, 50 Hz. Turns on the primary winding is 200.

Calculate

(i) The maximum value of flux in the core,

(ii) The core loss.

Question.

The rudder motor of a Ward-Leonard type steering gear is a compound-wound machine, details of which are given below. From this information find: (a) armature current, (b) the torque developed by the motor, (c) output power of motor. Armature — volts 90, resistance 0.02880, rev/min 370. 1R drop over armature may be taken as 8.5V. Shunt field — separately excited from 110V supply, resistance 65Q, turns per pole 1000. Series field — separately excited by prime mover line current of 325A, turns per pole 11. Torque Nm = (armature current (A) x flux (kWb) per pole x 10-4 X 6.8) = 15. M.M.F per pole (At)

3000 3500 4000 4500 5000 5500 6000 Flux per pole (kWb)

2500 2700 2860 2990 3100 3190 3275

Question

A 175kVA, 6600/440V, single-phase transformer has an iron loss of 2.75k\V. The primary and secondary windings have resistances of 0.417 and 0.00150 respectively. Calculate the efficiency on full load when the power factor is 0.9.

Question

A 550kVA, 50Hz, single-phase transformer has 1875 and 75 turns in the primary and secondary windings respectively. If the secondary voltage is 220V, calculate (a) primary voltage, (b) primary and secondary currents, (c) maximum value of flux.

Question

If an alternator supplies' the following loads: (a) 200k W lighting load at unity power factor, (b) 400kW induction-motor load at 0.8 (lagging), power factor, (c) 200kW synchronous-motor load, find the power factor of the synchronous-motor load, to give an overall power factor of 0.97 (lagging).

Question

A single-phase, 50Hz transformer, has a core with a square cross-section, each side being 270mm. The " transformation ratio is 3500/440V, and the maximum flux density in the core is not to exceed 1.4T. Find the number of turns of the windings required if the frequency is 50Hz.

Question

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

A 200V, long-shunt compound-wound generator has a full-load output of 20kW. The various resistances are as follows; armature (including brush contact) 0.15Ω, series Held 0.025Ω, interpole field 0.028Ω, shunt field (including the field-regulator resistance) 1150. The iron losses at full load are 780W, and the friction and windage losses 59OW. Calculate the efficiency at full load.

Question

A 500V, three-phase alternator supplies a balanced delta-connected load iu parallel with a balanced star-connected load. The delta load is 30kW at a power factor of 0.92 (leading) and the star load is 40k\V at a power factor of 0.S5 (lagging). Calculate the line current and the power factor of the supply.

Question

Two shunt generators work in parallel. Each has an armature resistance of 0.015Ω and a shunt-field resistance of 85Ω . Machine A is excited so that its e.m.f. is 600V, while the other machine B is excited so that its e.m.f. is 620V. What is the output of each machine when they jointly supply a load of 2500A and what is the busbar voltage?

Question

A shunt-wound generator has a magnetisation-curve given by the figures below. The total resistance in the field circuit is 20Ω and the armature resistance is 0.02Ω. With the machine on load, estimate the e.m.f. generated and the armature current when the terminal voltage of the machine is 140V.

Field current (A)—amperes

1.2 2.8 5.0 7.0 7.7 9.0 11.0

Generated e.m.f. (E)—volts

46 88 126 149 154 162 168

Question

Three d.c. generators connected in parallel, each supply a load of 640A to a set of 220V busbars. The e.m.f. of one generator is raised from 220V to 235V. If the load and the resistances are constant, determine the current supplied from each generator and the voltage at the busbars.

Question

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 the same direction, a load of 78A is taken from the mam. If the resistance of the main (lead and return) is 0.25Ω per

Question

A kettle, when connected to a 220V d.c. supply, boils 1 litre of water from 11°C in 3.5 min. Calculate the percentage time difference when the water is boiled, by connecting the kettle to a 220V, 50Hz a.c. supply. The inductance of the element of 0.05H. Take 1 litre of water to have a mass of lkg and its specific heat capacity as 4.2kJ/kg°C.

Question

A 2000 KVA, 3 phase, 8 pole alternator runs at 750 r.p.m. in parallel with other machine on 6000 V bus bars. Find synchronizing power on full load 0.8 p.f. lagging per mechanical degree of displacement and the corresponding synchronising torque. The synchronous reactance is 6 ohm per phase.

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