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BSNL TTA 

Question Paper-2007

Electrical Engineering

Q.1.In a D.C. generator, if the brushes are given a small amount of forward shift, the effect of armature is

• Totally demagnetizing
• Totally magnetizing
• Partly demagnetizing and partly cross magnetizing
• Totally cross magnetizing

Q.2.The air gap between stator and armature of an electric motor is kept as small as possible

• To get a stronger magnetic field
• To improve the air circulation
• To reach the higher speed of rotation
• To make the rotation easier.

Q.3.Two series motors are coupled. One motor runs as generator & other as motor.The friction losses of the two machines will be equal when

• Both operates at same voltage
• Both have same back emf
• Both have same speed
• both have same excitation

Q.4.Plugging of D.C. motor is normally executed by

• Reversing the field polarity
• Reversing the armature polarity
• Reversing both the armature and field polarity
• Connecting a resistance across the armature.

Q.5.Transformer oil transformer provides

• Insulation and cooling
• Cooling and lubrication
• Lubrication and insulation
• Insulation, cooling and lubrication

Q.6.Leakage fluxes of transformer may be minimized by

• Reducing the magnetizing current to the minimum
• Reducing the reluctance of the iron core to the minimum
• Reducing the number of primary and secondary turn to the minimum
• Sectionalizing and interleaving the primary and secondary windings

Q.7.Electric power is transformed upon one coil to other coil in a transformer

• Electrically
• Electro Magnetically
• Magnetically
• Physically

Q.8.The most suitable and economical connection for small high voltage transformer isa.

• Star- Delta connection
• Delta- Delta connection
• Delta- Star connection
• Star- Star connection

Q.9.An alternator is said to be over excited when it is operating at

• Unity power factor
• Leading power factor
• Lagging power factor
• Either lagging or leading power factor

Q.10.In an A.C. machine, the armature winding is kept stationary while the field winding is kept rotating for the following rason

• Armature handles very large currents and high voltages
• Armature friction involving deep slots to accommodate large coils is easy if armature is kept stationary
• Ease of cooling the stator than rotor
• None of the above.

Q.11.In a synchronous motor, the torque angle is the

• Angle between the rotating stator flux and rotor poles
• Angle between the magnetizing current and back emf
• Angle between the supply voltage and back emf
• None of the above

Q.12.A 3-phase synchronous motor is said to be "floating" when it operates

• On no load and without loss
• On constantly varying load
• On pulsating load
• On high load and variable supply voltage

Q.13.Speed of synchronous motor depends upon

• Number of poles
• Supply frequency
• Both (a) and (b)
• Neither (a) nor (b)

Q.14.Imbalance in the shaft of an induction motor occurs due to

• Slip rings
• Overheating of winding
• Non uniform of air gap
• Rigid construction

Q.15.Squirrel cage induction motor has

• Zero starting torque
• Very small starting torque
• Medium starting torque
• Very high starting torque

Q.16.The principle of operation of a 3-phase induction motor is similar to that of a

• Synchronous motor
• Repulsion - start induction motor
• Transformer with a shorted secondary
• Capacitor - start, induction - run motor

Q.17.The speed/load characteristics of a universal motor are similar to those

• D.C. shunt motor
• D.C. series motor
• A.C. motor
• None of the above

Q.18.Single phase A.C. motor generally used for vacuum cleaners is

• Universal motor
• Repulsion motor
• Hysteresis motor
• Reluctance motor

Q.19.Buchholz relay is used for the protection of

• Switch yard
• Transformers
• Alternators
• Transmission lines

Q.20.The type of braking used in traction system is

• Mechanical braking
• Electro - pneumatic braking
• Vacuum braking system
• All the above

Q.21.The function of processing zener diode in a UJT circuit used for triggering of SCRs is to

• Expedite the generation of triggering pulses
• Delay the generation of triggering pulses
• Provide a constant voltage to UJT to prevent erratic firing
• Provide a variable voltage to UJT as the source voltage changes

Q.22.The frequency of a ripple in the output voltage of a 3 - phase semi converter depends upon

• Firing angle and load resistance
• Firing angle and supply frequency
• Firing angle and load inductance
• Only on load circuit parameters

Q.23.The SCR is turned off when the anode currents falls below

• Forward current rating
• Break - over voltage
• Holding current
• Latching

Q.24.V-I characteristics of emitter of a UJT is

• Similar to CE with linear and saturation region
• Similar to FET with a linear and pinch of region
• Similar to tunnel diode in some respects
• Linear between the peak point and valley point

Q.25.A transformer works on

• DC
• AC
• AC & DC both
• Neither AC not DC

Q.26.Which of the following device is used in transformer?

• Tube light
• Electric heater
• Mobile phone
• Rectifier module

Q.27.Earth electrodes can be in the form of

• rods or piper
• stripes
• plates
• any of above

Q.28.Carbone or metal brushes are used in

• DC generators only
• AC generators only
• Both AC & DC generation
• None of above

Q.29.Energy is lost due to Joule's heating effects in winding of transformer. This is called

• Copper loss
• Eddy current loss
• Flux loss
• None

Q.30.In refrigeration cycle heat is lost in

• Cooling coil
• Condenser
• Compressor
• Expansion valve

Q.31.The power factor of AC circuit is

• R/X
• R/Z
• Z/R
• Zero

Q.32.Silicon controlled output is good if ripple factor is

• Switch
• Transformer
• Amplifier
• None of above

Q.33.The rectifier output is good if ripple factor is\

• More
• Less
• Constant
• None of above

Q.34.Protective relays can monitor large AC current by means of

• Current transformer
• Potential transformer
• Micro transformer
• None of above

Q.35.The combines AM of two similar batteries connected in parallel is:

• halved
• doubled
• remain constant
• none of above

Q.36.The current in circuit having 5 V EMI source and 10 Ohm resistance is:

• 2 Amp
• 50 Amp
• 5 Amp
• ½ Amp

Q.37.The chopper is a device to change

• Voltage
• Current
• Frequency
• None of these

Q.38.The power consumption, in case of centrifugal loads (like pump, fan, blower etc) is
proportional to:

• speed
• square of speed
• cube of speed
• none of these

Q.39.Which of these need to be measured after rewinding the motor:

• no load current
• air gap
• winding resistance
• all of the above

Q.40.Five percent increase in supply frequency will change the synchronous speed of motor by:

• -5%
• +5%
• -10%
• +10%

Q.41.Which of the following is the best inverter?

• square wave inverter
• sine wave inverter
• pure sine wave inverter
• triangular wave inverter

Q.42.For driving a motor in a tape recorder or record player, the motor used is generally:

• a synchronous motor
• a hydraulic motor
• an induction motor
• a dc series motor

Q.43.The DC motor starter used with a constant speed shunt motor is:

• 2 point starter
• 3 point starter
• 4 point starter
• 5 point starter

Q.44.A commutator in a DC motor converts

• AC to DC
• DC to AC
• Both AC to DC and DC to AC
• None of these

Q.45.Two transformers running in parallel will share the load according to their:

• leakage reactance
• pu impedance
• efficiency
• rating

Q.46.The size of the Earth Wire is determined by:

• the ampere capacity of the service wires
• the atmospheric conditions
• the voltage of service wires
• none of these

Q.47.The function of lightning arrester is:

• to limit the short circuit fault current
• to provide path to high voltage surge to earth
• to reduce arcing
• none of these

Q.48.Surge protector provide:

• high impedance to normal voltage
• low impedance to surge
• both (a) and (b)
• none of these

Q.49.Earthing is necessary to give protection against

• voltage fluctuation
• overloading
• danger of electric shock
• high temperature of conductors

Q.50.The primary function of fuse is to

• protect the appliance
• open the circuit
• prevent excessive current
• protect the line

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