Transformer questions

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Q1:- what is meant by the leakage flux of transformer
1. It is the flux which is linked with the primary and the secondary winding
2. It is that part of the magnetic flux which is significant for radio interference
3. It is the magnetic flux which is linked the only with the primary or only with the secondary winding
4. The leakage flux in the transformer is the influx whose path is exclusively through the air

ANSWER:-3

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Q2:- why are Transformer core laminated

1. Laminated core are cheaper than solid Core

2. There are fewer Eddy current losses in laminated Core

3. There are fewer hysteresis losses in laminated Core

4. There is less coming as compared to solid Core

ANSWER:-2

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Q3:- hysteresis loss in a transformer depends upon the

1. Applied voltage
2. Type of core material
3. Number of laminations
4. Reactance of the winding

ANSWER:-2

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Q4:- current transformer is used to measure 100 A current by 5 ampere metre the current transformer is a

1. Step Up transformer
2. Step down transformer
3. Power transformer
4. Distribution transformer

ANSWER:-1

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Q5:- it is economical to use an auto transformer when the Transformer ratio is

1. Low
2.high
3. Neither too high no to low
4. None of these

ANSWER:-1

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Electrical questions

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Q1:- when is the mechanical power developed by a DC motor maximum
1. Back EMF is equal to applied voltage
2. Back EMF is equal to zero
3. Back EMF is equal to the half of applied voltage
4. None of the above

ANSWER:-3

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Q2:- internal characteristic of a DC generator is plotted between the

1. Field current and voltage generated no load

2. Armature current and voltage generated no load

3. Armature current and voltage generated after armature reaction

4. Field current and voltage generated on load

ANSWER:-3

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Q3:- the bridge method in transformer will

1. Check Transformer winding
2. Check windings voltages
3. Find ratio of induced voltage
4. Result in short circuit loss

ANSWER:-3

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Q4:- what is the effect of the field failure of salient pole synchronous motor connected with infinite bus

1. Reduce motor torque and speed
2. Not charged motor torque and speed
3. Stop the motor
4. Reduce not at work but motor will continue to run at synchronous speed

ANSWER:-4

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Q5:- Wanger's earthing device is used in AC Bridge for

1. Shielding the bridge element
2. Eliminating the dtray electrostatic field effect
3. Eliminating the effect of earth capacitance
4. Eliminating the effect of the inter component capacitance

ANSWER:-2

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Competitive exams questions

Q1:- in which of the following Transformers is the secondary winding always kept closed
1. Current transformer
2. Potential transformer
3. Power Transformers
4. Distribution transformer

ANSWER:-1

Q2:- two holes are drilled in the disc on a diameter of energy metre to

1. Increase ventilation

2. Reduce the weight of disc

3. Eliminate creeping on no load

4.Increase deflecting torque

ANSWER:-3

Q3:- which of the following instruments has the highest torque/ weight ratio among the given instrument

1. Attraction type MI instrument
2. Repulsion type MI instrument
3. Permanent magnet moving coil instrument
4. Electrodynamometer instrument

ANSWER:-3

Q4:- if current through the operating coil of moving iron instrument is doubled the operating force becomes

1. One and a half Times
2. 2times
3. 3 times
4. 4 times

ANSWER:-4

Q5:- in moving iron instruments the iron moves in a direction to cause

1. Coil inductance to be constant
2. Mutual inductance to be minimum
3. Minimum reluctance path
4. Decrease in the flux passing through it

ANSWER:-3

DC machine

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Q1:- the direction of rotation of a DC motor is reversed by
1. Riveting armature connections
2. Interchanging the armature and field connections
3. Adding resistance to the field circuit
4. Reversing supply connections

ANSWER:-1

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Q2:- the s i unit of conductivity is

1. Ohm metre

2. Ohm per metre

3. Mho meter

4.mho/m

ANSWER:-4

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Q3:- a piece of oil soaked paper has been inserted between the plates of a parallel plate capacitor then the potential difference between the two plates will be

1. Increase
2. Decrease
3. Remains unchanged
4. Become zero

ANSWER:-2

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Q4:- the current drawn by tungsten filament lamp is measured by an ammeter. the ammeter reading under steady state condition will be the ammeter reading when the supply is switched on

1. Same as
2. Less than
3. Greater than
4. Double

ANSWER:-2

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Q5:- Tesla is same as

1. Weber per metre
2. Weber metre square
3. Farad /metre
4. Henry per metre square

ANSWER:-2

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DC machine

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Q1:-which of the following statement is correct in case of single phase transformer ?

1.in this a varying current appears in primary winding that creates varying magnetic flux in transformer's core
2.it creates varying magnetic field in secondary winding that induces electromotive force (EMF) or voltage 
3.it carries inductive coupled conductor
4.all of the above 

ANSWER:-4

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Q2:-the surge impedance of over head transmission lines range from

1.30 to 60 ohms

2.300 to 600 ohms

3.2500 to  6500 ohms

4.10000 to 40000ohms

ANSWER:-2

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Q3:-Nodal analysis applies to 

1.KVL & ohm's law
2.KCL  & superposition
3.KVL & superposition 
4.KCL & superposition

ANSWER:-2

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Q4:- in a DC machine how are the computing pole winding connected

1. In series with shunt winding
2. Parallel to the shunt winding
3. In series with the armature winding
4. Parallel to the armature winding

ANSWER:-3

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Q5:- which of the following winding is connected in series with armature winding of DC machine

1. Series winding
2. Auxiliary series winding
3. Compensating winding
4. Communicating on winding

ANSWER:-4

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DC Machine

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Q1:-The efficiency of a motor is generally expressed as 

1. 90 %
2. 75 %
3. 60 %
4. 99 %

ANSWER:-1

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Q2:-The efficiency of a generator is usually expressed as 

1. (input - losses ) / input
2. output / input 
3. output /(output+input)
4.  none of these 

ANSWER:-3

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Q3:-In swinburne test on a dc machine 

1. all the losses cannot be determined individually
2. copper losses  cannot be determined individually
3. mechanically and iron losses can not be determined individually
4. none of the above

ANSWER:-2

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Q4:-Two  dc machines 500 kw each are tested by Hopkinson test. The power input would be of the order of 

1. 500 kw 
2. 100 kw
3. 1000 kw
4. none of these

ANSWER:-2

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Q5:-The no load voltage of a generator is 230 v and the rated load voltage is 200 v then the voltage regulation

1. 5%
2. 10%
3. 15%
4. 20%

ANSWER:-3

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DC Machine

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Q1:-A shunt generator has a speed of 500 rpm when delivering 100 kw at 200 v. it run as a motor taking an input of 100 kw from 200 v mains the speed will be 

1. 500 rpm
2. less than 500 rpm
3. more than 500 rpm
4. none of these 

ANSWER:-2

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Q2:-Swinburne test can not be used or 

1. series motor
2. shunt motor
3. compound motor
4. none of these

ANSWER:-1

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Q3:-In Hopkinson test on a pair of shunt machines 

1. the armature currents of the motor and generator are equal
2. the armature current of the motor is less than that of generator
3. the armature current of the generator is less than that of the motor 
4. none of these 

ANSWER:-2

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Q4:- In a dc machine the maximum losses occur due to 

1. iron losses
2. mechanical losses
3. copper losses
4. none of these

ANSWER:-3

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Q5:-The efficiency of a motor is generally expressed as

1. (input -losses) / input
2. output / input
3. output / (output+losses)
4. none of the above

ANSWER:-1

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Alternate Questions

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Q1:-Which of the following class is mainly used in electrical machines for insulation

1. class Y
2. class A
3. class F
4. class C

ANSWER:-2

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Q2:-When the excitation of synchronous motor is varied 

1. the pf and the armature current varies 
2. the pf varies but the armature current does no vary 
3. the armature current varies but the pf does not vary 
4. neither the pf nor the armature current varies

ANSWER:-1

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Q3:-For steady flux and good mechanical properties the material extensively used for magnetic circuit is 

1. iron 
2. cast iron
3. grey cast iron
4. cast steel

ANSWER:-3

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Q4:-The resistance of insulation material is 

1. proportional to its resistivity
2. inversely proportional to its resistivity
3. independent of the temperature 
4. independent of material

ANSWER:-1

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Q5:-When a substance is placed in a magnetic field its ability to get magnetised depends upon its 

1. permittivity
2. permeability
3. susceptibiltiy
4. none of these

ANSWER:-3

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Semi Conductor

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Q1:-The Ge crystal behave as an insulator at

1. 0 k
2. 273 k
3. 5 k
4. none of these 

ANSWER:- 1

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Q2:-In a full wave rectifier the diode conduct for 

1. one half cycle
2. full cycle
3. alternate half cycle 
4. none of these

ANSWER:-3

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Q3:-The maximum efficiency of half wave rectifier is 

1. 33.33 %
2. 40.6 %
3. 50 %
4. 68 %

ANSWER:-2

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Q4:-The  peak inverse voltage in case of a bridge rectifier circuit for each diode is 

1. Em
2. 2 Em
3. 3 Em
4. 4 Em

ANSWER:-1

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Q5:- Peak inverse voltage for a full waver rectifier is peak value of input voltage 

1. Em
2. 2Em
3. 3Em
4. 4Em

ANSWER:-2

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Semi Conductor

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Q1:-An electron tube can only operate when

1. anode is negative with respect to cathode
2. anode is positive with respect to cathode 
3. anode must be at zero potential with respect to cathode
4. anode to cathode

ANSWER:-2

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Q2:-The process of conversion ac into dc is called

1. amplification 
2. modulation 
3. rectification 
4. factorisation

ANSWER:-3

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Q3:-The semiconductor are replacing electron tube because they are

1. light in weight 
2. smaller in weight 
3. longer in life and greater in ruggedness
4. all of the above

ANSWER:-4

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Q4:-Oxide Coated cathode is used in

1. low power tubes 
2. medium power tubes
3. high power tube
4. medium and high power tubes

ANSWER:-1

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Q5:-The metal from which the electrons are emitted is called 

1. an emitter
2. a cathode
3. an emitter or a cathode
4. none of these

ANSWER:-3

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Transformer

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Q1:-Transformer are rated in

1. kilo watt
2. kilo watthour
3. kilo volt amperes
4. kilo volt

ANSWER:-3

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Q2:-Which of the common method of cooling a power transformer

1. air cooling 
2. air bast cooling
3. oil cooling 
4. natural cooling 

ANSWER:-3

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Q3:-The efficiency of a power transformer is maximum at

1. nearly full load 
2. 1/2 full load 
3. 1/4 full load
4. 1/8 full oad

ANSWER:-1

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Q4:-What type of core is used for a high frequency transformer

1. open iron core
2. closed iron core
3. shell type iron core
4. air core

ANSWER:-4

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Q5:-Which of the statements below is true about the auto transformer?

1. it has two separate windings connected in series externally
2. it has only one windings .
3. it can only step down the voltage.
4. it is most suitable for power transformation.

ANSWER:-2

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Transforms

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Q1:-Transformer works on the principle of 

1. self induction 
2. mutual induction
3. faraday's law of electro magnetic induction
4. self and mutual induction

ANSWER:-2

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Q2:-If dc supply is given to a transformer it will 

1. work
2. not work
3. given lower voltage than the rated voltage on secondary side
4. burn the winding

ANSWER:-4

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Q3:-Different types of transformer are 

1. core type 
2. shell type 
3. berry type 
4. all of these

ANSWER:-4

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Q4:-The self induced voltage of a coil depends upon 

1. the voltage applied to the coil 
2. the shape of the iron core
3. the shape of the bobbin 
4. the number of turns of the coil 

ANSWER:-4

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Q5:-Which of the following is an instrument transformer

1. bell transformer
2. adjustable transformer
3. ignition transformer
4. current transformer

ANSWER:-4

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Measuring Systems And Instrumentation

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Q1:-In a moving coil instrument the deflecting torque is proportional to 

1. current 
2. square of the current 
3. square root of the current 
4. sine of the measurand

 ANSWER:-1

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Q2:-Electrostatic instruments are normally used for 

1. low current measurements
2. high current measurements
3. low voltage measurements
4. high voltage measurements

ANSWER:-4

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Q3:-No eddy current and hysteresis losses occur in 

1. Electro static instruments
2. PMMC type instruments
3. moving iron instruments
4. none of these

ANSWER:-1

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Q4:-Creeping is observed in

1. watt hour meter
2. power factor meters
3. wattmeter
4. ammeter

ANSWER:-1

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Q5:-A C.T. is overload when 

1. the load connected to it is less than its burden
2. its terminals are short circuited
3. when its terminals are open circuited 
4. when the primary current is 110 % of its rated value

ANSWER:-3

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DC Machine

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Q1:-One dc motor drive another dc motor . the second dc motor when excited and driven it 

1. run
2. does not run as generator
3. run as a generator
4. also runs as motor

ANSWER:-3

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Q2:-In dc shunt motor it the terminal voltage is reduced to half and torque remains the same then

1. speed will be half and armature current also will be half
2. speed will be half but armature current remains the same\
3. speed will be half and armature current becomes double 
4. speed and armature current will remains the same.

ANSWER:-3

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Q3:-The armature of dc motors is laminated 

1. to reduced the hysteresis losses
2. to reduced the eddy current losses
3. to reduced the inductivity of armature
4. to reduced the mass of the armature

ANSWER:-2 

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Q4:-The direction of rotation of a dc shunt motor is reversed by 

1. reversing armature connections
2. interchanging the armature and field connection 
3. adding resistance to the field circuit
4. reversing supply connection

ANSWER:-1

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Q5:-The efficiency of any electrical machine /apparatus will be high if

1. its losses are minimum 
2. its losses are more 
3. voltage applied is constant
4. the current drawn is minimum.

ANSWER:-1

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Measuring Systems And Instrumentation

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Q1:-The VA rating of instrument transformers is normally near

1. 0.1 VA
2. 10 VA
3. 100 VA
4. none of these

ANSWER:-2

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Q2:-The main error in a dynamometer type watt meter is due to 

1. pressure coil inductances
2. pressure coil capacitances
3. mutual inductionces
4. none of these

ANSWER:-1

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Q3:-Induction type watt meter operation is based on 

1. electro static forces
2. thermo electric effect
3. hall effect
4. eddy current effect

ANSWER:-1

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Q4:-The error in C.T. are mainly due to 

1. leakage flux
2. excitation emf required
3. core losses
4. copper losses

ANSWER:-3

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Q5:-Schering bridge is used to measure

1. dielectric loss
2. the inductance
3. low resistance 
4. mutual inductance

ANSWER:-1

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Transforms

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Q1:-The transformer is commonly used because 

1. it has high efficiency
2. frequency remains constant 
3. construction cost per KVA less as compared to other machine 
4. all of the above

ANSWER:-4

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Q2:-In an ideal transformer on no load the primary applied voltage is balanced by 

1. the secondary voltage 
2. the drop across resistance and reactance.
3. the secondary induced emf
4. the primary induced emf

ANSWER:-3

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Q3:-The voltage transformation ratio is 

1. E1/E2
2. N1/N2
3. E2/E1
4. none of these

ANSWER:-3

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Q4:- A transformer operates 

1. always at unity pf
2. has its own pf 
3. at a pf below a particular value
4. at pf depending on the pf of the load

ANSWER:-4

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Q5:-Which of the following is a correct statement about eddy current ?

1. eddy current improve the efficiency of a motor
2. eddy currents do not influence the movement 
3. eddy currents heat up the metal parts 
4. eddy currents are used are winding
5. ANSWER:-3

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DC Machine

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Q1:-A dc generator can be termed as 

1. rotating amplifier 
2. promer mover
3. power pump
4. none of these 

ANSWER:- 1

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Q2:-which of the following dc motors is suitable for high starting toque

1. shunt motor
2. commutative compound motor
3. series motor
4. compound motor

ANSWER:-3

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Q3:-The function of compensating winding placed in slots in the pole shoes is 

1. to neutralise the armature reaction effect
2. to avoid unequal distribution of current at brushes
3. to avoid short circuit current
4. none of these

ANSWER:-2

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Q4:-The function of the compensating windings placed in slots in the pole shoes is

1. to neutralise cross magnetising effect
2. to netralise the demagnetiseing effect
3. to neutralise both the effects
4. to avoid flash over around the commutator

ANSWER:-4

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Q5:- For which of the following dc motors is the typical field of application mentioned ?

1. shunt motor : electric trains
2. series motor : machine tools 
3. series motor : belt drive 
4. compound motor : fly wheel drive 

ANSWER:-4

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Transformer

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Q1:-Shell type transformer is commonly used because

1. it has more magnitude flux leakage 
2. it has less magnetic flux leakage
3. it has two magnetic paths
4. both 2 and 3 

ANSWER:-4

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Q2:-The steel for construction of transformer core is made to have 

1. high permeability and low hysteresis loss
2. low permeability and high hysteresis loss
3. low permeability and high hysteresis loss
4. high permeability and high hysteresis loss

ANSWER:-1

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Q3:-The transformer oil used in transformers provides 

1. insulation and cooling
2. cooling and lubrication 
3. insulation and lubrication 
4. insulation cooling and lubrication

ANSWER:-4

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Q4:-The use of higher flux density in transformer design

1. increases the weight per KVA
2. decreases the weight per KVA
3. increases the weight per KVA
4. decreases the weight per Kw

ANSWER:-2

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Q5:-What type of core is used for a high frequency transformer ?

1. open iron core 
2. air core
3. closed iron core
4. none of these

ANSWER:-2

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DC Machine

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Q1:-Which of the following statements is incorrect in dc shunt generators about hysteresis loss?

1. it can be minimized by laminating the armature
2. it is independent of laminating thickness
3. it depends upon the supply frequency 
4. none of these

ANSWER:-1

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Q2:- An ideal dc generator has a regulation of 

1. 0 %
2. 50 %
3. 75 %
4. 100 %

ANSWER:-1

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Q3:-Which of the following methods is most economical for finding the no load losses of a large dc shunt motor ?

1. hopkinson's test
2. swinburne's test
3. retardation test
4. none of these

ANSWER:-2

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Q4:-Why is the air gap between stator and armature of an electric motor kept as small as possible

1. to get strong magnetic field 
2. to make the rotation easier 
3. to reach a higher speed of rotation
4. to improve the air circulation

ANSWER:-1

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Q5:-The generator of a power station produces an electric pressure by 

1. conversion of heat
2. magnetic induction 
3. conversion of light
4. mechanical pressure
5. ANSWER:-4 

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Induction Motor

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Q1:- In a 3- phase induction motor the current is produced in the rotor conductors by 

1. giving a.c. supply 
2. giving dc supply 
3. induction effect 
4. none of these

ANSWER:- 3

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Q2:-In a 3-phase induction motor slip for maximum torque , in terms of rotor resistance r2

1. independent of r2
2. directly proportional to 2
3. inversely proportional to r2
4. none of these

ANSWER:-2

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Q3:-If any two phase of the three phase supply are interchange motor will

1. run in the same direction 
2. stop running 
3. run in the reverse direction 
4. draw high current 

ANSWER:-3

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Q4:-At full load the current induced int he rotor conductor of a 3- phase squirrel cage induction motor is 

1. more than rated current 
2. less than rated current 
3. nearly equal to rated current 
4. none of these 

ANSWER:-3

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Q5:-The frequency of the induced emf in the rotor circuit is 

1. maximum at stand still 
2. zero at stand still
3. maximum at synchronous speed
4. none of these.

ANSWER:-1

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Measuring Systems And Instrumentation

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Q1:-The megger voltage for testing 250 v installation should be

     1.       1000 v

     2.       500 v

     3.       300 v

     4.       100 v

ANSWER:-2

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Q2:-The direction of rotation of 3- phase revolving field can be changed by interchanging

     1.       Rand Y phase only

     2.       B and Y phase only

     3.       R and B phase only

     4.       Any two phase

ANSWER:-4

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Q3:-The synchronous speed of the revolving field depends upon.

      1.       Number of poles

      2.       Supply frequency

      3.       Flux

      4.       1 and 2

ANSWER:-4

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Q4:-The rotor of a 3-phase induction motor rotates in the same direction as the direction of revolving field because of

  
      1.       Faraday’s laws of electro magnetic induction

      2.       Lenz’s law

      3.       Fleming’s right hand rule

      4.       None of these

ANSWER:-2

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Q5:-For induction motors normally

      1.       The rotor winding is connected to supply and the stator winding is short circuited

      2.       The stator winding is connected to supply and the rotor winding is short circuited

      3.       Both the stator and the rotor windings are connected to supply

     4.       The stator winding is connected to supply and the rotor winding is open circuited

ANSWER:-2

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Switch Gear And Protection

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Q1:- When fault occur on a system

1. voltage of 3- phase become balance
2. voltage of 3- phase become unbalance
3. voltage of 3- phase first balance and then unbalance 
4. none of the above 

ANSWER:- 2

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Q2:-The voltage of short transmission line is

1.       20 kv or less

2.       40 kv or above

3.       110 kv or less

4.       66 kv or above

ANSWER:-1

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Q3:-The length of medium transmission line is lying between

1.       50 km to 150 km

2.       150 km to 200 km

3.       100 km to 200 km

4.       Above 100 km

ANSWER:-1

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Q4:-The voltage of medium transmission line is lying is

1.       100kv to 220 kv

2.       220 kv to 660 kv

3.       22 kv to 100 kv

4.       None of the above

ANSWER:-3

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Q5:-The length of long transmission line is

1.       More than 200 km

2.       More than 100 km

3.       More than 150 km

4.       More than 220km

ANSWER:-3

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