CIRCUIT BREAKER THEORY

CIRCUIT BREAKER

The main difference between a fuse and circuit breaker is that under fault condition the fuse melts and it is to be replaced whereas the circuit breaker can close or breaker the circuit without replacement.

Requirements of circuit breakers:-

The power association with the circuit breakers is large and it forms the link between the consumers and supplies and suppliers. The necessary requirements of circuit breakers are as follows

    1.The normal working current and the short circuit current must be safely interrupted by the circuit breaker

    2.The faulty section of the system must be isolated by circuit breaker as quickly as possible keeping minimum delay

    3.It should not operate with flow of over current during healthy conditions. 

   4. The faulty circuit only must be isolated without affecting the healthy one.

BASIC ACTION OF A CIRCUIT BREAKER

As shown in fig the elementary diagram of a circuit breaker. It consists of two contacts a fixed contact and a moving contact . A handle  is attached at the end of the moving contacts. It can be operated manually or automatically. The automatic operation needs a separate mechanism which consists of a tip coil. The trip coil is energized by secondary of the current transformer. The terminals of circuit breaker are brought to power supply.

Under normal condition working conditions the emf produced in the secondary winding of the transformer is insufficient to energize the trip coil completey for its operation. Thus the contacts remain in closed position carrying the normal working current. The contacts can be opened manually also by handle.

       Under abnormal or faulty conditions high current in the primary winding of the current transformer induced sufficiently high emf in the secondary winding so the trip coil is energized. This will start opening motion of the contacts. The contacts are moved towards right away from fixed contacts.

As we have seen already the separation of contacts will not lead to breaking or interruption of circuit as an arc is struck between the contacts. The production of arc delays the current interruption and in addition to this it becomes large amount of heat which may damage the system or the breaker. Thus it becomes necessary to extinguish the arc as early as possible in minimum time, so that heat produced will lie within the allowable limit. This will also ensure that the mechanical stresses produced on the parts of circuit breaker are less.

The time interval which is passed in between the energization of the trip coil to the instant of contact separation is called the opening time. It is dependent on fault current level.

The time interval from the contact separation to the extinction of arc is called arcing time. It depends not only on fault current but also on availability of voltage for maintenance of arc and mechanism used for extinction of arc.

Electrical Instruments and measurements

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Q1:- The consumption of M.I. instrument as compared of M.C. instrument is

        1.       same

        2.       more

        3.       less

        4.       very small

ANSWER:-2

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Q2:- The most commonly used type of single phase energy meter is

      

       1.       dynamometer type

       2.       electrostatic type

       3.       induction type

       4.       moving coil type

ANSWER:-3

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Q3:- The energy meter used for measuring energy of a d.c. circuit is

       

       1.       ampere hour type

       2.       induction type

       3.       electrostatic type

       4.       dynamometer type

ANSWER:-1

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Q4:- The pressure coil consists of

      1.       more number of turns of fine wire

      2.       less number of turns of fine wire

      3.       less number of thick wire

      4.       more number of turns of thick wire

ANSWER:-1

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Q5:- The current coil of a single phase energy meter is wound on

      1.       one limb of the laminated core

      2.       both the limbs of the laminated core with different turns

      3.       both the limbs of the laminated core  with same number of turns

     4.       the centre of the limb on the laminated core with same number of turns

ANSWER:-3

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UPRVNL QUESTIONS

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Q1:- The function of a centrifugal pump in 1- phase induction motors is to

      1.       cut off starting winding at appropriate time

      2.       cut the capacitor during running condition

      3.       protect the motor from overloading

      4.       improve the starting performance of the motor

ANSWER:-1

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Q2:- In a super heater in a steam plant the

      1.       pressure rises and temp remains unchanged

      2.       pressure rise and temp drops

      3.       temp rises and pressure drops

      4.       temp rises and pressure remains unchanged

ANSWER:-4

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Q3:- For dc shunt motor control by armature resistance variations is best suited for

     1.       constant torque drive

     2.       variable torque drive

     3.       variable power drive

     4.       constant power drive

ANSWER:-1

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Q4:- In a RLC series circuit at resonance

     1.       current is minimum , power factor is zero

     2.       current is maximum , p.f. is zero

     3.       current is maximum , p.f. is unity

    4.       current is minimum , p.f. is unity

ANSWER:-3

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Q5:- The V- curve of a synchronous motor the relationship b/w

     1.       armature current and supply voltage

     2.       field current and armature current

     3.       excitation current and back emf

    4.       field current and p.f.

ANSWER:-2

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Electrical Instrumentation Question

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Q1:- The deflecting torque can be produced by

1. gravity control
2. spring control
3. air friction
4. magnetically

ANSWER:-4

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Q2:- Chemical effect is used for the operation of 

1. voltmeter 
2. ammeter
3. ampere hour meter
4. kwh meter

ANSWER:-3

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Q3:- The meter used for measuring electrical energy of consumer is called 

1. wattmeter
2. ampere hour meter
3. kwh meter
4. avometer

ANSWER:-3

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Q4:- The meter used for measuring current of an electrical circuit is called 

1. voltmeter 
2. ammeter
3. potentiometer
4. multimeter

ANSWER:-2

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Q5:- The damping torque can be produced by 

1. eddy currents 
2. gravity control
3. electrostatically 
4. thermally 

ANSWER:-1

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Lucknow Metro Question

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Q1:- The direction of electromagnetically induced current in a circuit placed in varying magnetic field may be found by

1. feleming's left hand rule
2. fleming's right hand rule and lenz's law 
3. joules's law 
4. right hand thumb rule 

ANSWER:- 2

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Q2:- Reactance in p.u. behind the fault point in a power system is 0.5 . the fault MAV in p.u. will be 

1. 2 x 10^3
2. 0.5 x 10 ^6
3. 2 x 10 ^6
4. 2

ANSWER:- 4

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Q3:- In differntia protection of bus bar the CT ratio of the CTs on both side are

1. equal and based on primary current of highest current carrying feeder
2. based on total expected fault current 
3. based on their respective feeder current 
4. equal and based on primary current lowest current carrying feeder

ANSWER:- 1

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Q4:- If the field of synchronous motor is under excited the power will be

1. more than unity 
2. unity 
3. lagging
4. leading 

ANSWER:- 3

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Q5:- If one of the 3- phase of synchronous motor is short ciruited motor will 

1. start 
2. not start
3. over heated 
4. fail to pull into synchronism

ANSWER:- 2 

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Lucknow Metro Questions

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Q1:- A large diversity factor means

1. large plant capacity is required 
2. increased the unit price of electricity
3. reduces the unit price of electricity
4. increases the maximum demand

ANSWER:-3

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Q2:-In protection of radial feeders as we go towards source end from father side of the feeder which statement is correct 

1. the time setting decreases and current setting increases progressively 
2. the time and current setting of relays goes on decreases progressively
3. the time and current setting of relays goes on increasing progressively 
4. the time setting increases and current setting decreases progressively 

ANSWER:-3

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Q3:- Merz Price protection of three phase star- delta transformers CTs ae connected as 

1. on star side of transformers CTs are connected in delta and on delta side of transformer CTs may be connected either in star or delta 
2. on star side of transformers CTs may be connected either in star or delta and delta side of transformer CTs are connected in star
3. on star side of transformer CTs are connected in delta and on delta side of transformer CTs are connected in star 
4. on star side of transformer CTs are connected in delta and on delta side of transformer CTs are connected in delta 

ANSWER:-3

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Q4:- Pumped storage plants are used as 

1. base load plants
2. peak as well as base load plants 
3. co generation plants 
4. peak load plants 

ANSWER:-4

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Q5:- In protection of parallel feeders fed at one end 

1. all the relays used are directional
2. either directional or non directional can be used 
3. both directional and non directional relays are used 
4. all the relays used are non directional 

ANSWER:-3

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Lucknow Metro Questions

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Q1:-In case of separately excited dc generator with constant speed when speed when field current  is increased 

1. the generated emf increased directly 
2. frequency of the generated emf reduces 
3. the generated emf reduces inversely 
4. frequency of the generated emf increases

ANSWER:-1

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Q2:- Iron losses in DC m/c take place in 

1. yoke only 
2. yoke and armature only 
3. armature winding only
4. armature core only

ANSWER:-4

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Q3:- The probability of occurrence is highest for 

1. line to ground fault 
2. three phase short circuit fault 
3. line to line fault 
4. double line to ground fault 

ANSWER:-1

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Q4:- In any electric circuit the flow of electron constitutes 

1. an electric current 
2. magnetic charge 
3. an electromotive force
4. an electric charge

ANSWER:-1

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Q5:- For power factor improvement the amount of capacitance required for star connected capacitor bank is 

1. half of thew delta connected banks 
2. three times less than delta connected banks
3. three times more than delta connected banks 
4. equal to delta connected banks 

ANSWER:-3

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Utilization of Electrical Energy Theory

Mean Spherical Candle power (M.S.C.P):-

It is defined as average of candle powers in all directions and in all plans from the source of light i.e. 
                 
                               
                     MSCP = (total flux in lumens )/ 4 pi

Mean Hemispherical Candle power (MHSCP):-

It is defined as average of candle powers in all directions and in all and in all plans from the source of light i.e. 

              MSCP = (total flux in lumens)/4pi

Utilization of Eectrical Energy Question

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Q1:- Reluctance motor is a 

1. self - starting type synchronous motors 
2. low torque variable speed motor 
3. variable torque motor 
4. low noise, slow speed motor

ANSWER:- 1

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Q2:- A reluctance motor is 

1. is compact 
2. has high cost 
3. requires starting gear
4. is provided with slip rings.

ANSWER:-1

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Q3:- Power factor of reluctance motor is 

1. nearly unity
2. always leading 
3. 0.8 lagging
4. 0.3 to 0.4 leading 

ANSWER:-4

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Q4:- The efficiency of reluctance motor is around 

1. 95 %
2. 80 %
3. 75 to 85 %
4. 60 to 75 % 

ANSWER:-4

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Q5:- A pole changing type squirrel cage induction motor used in derricks has 4, 8 and 24 poles. in this the lowest speed is used for 

1. lifting
2. hoisting 
3. lowering 
4. landing the road 

ANSWER:-4

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Electrical measuring of instruments Theory

Types of measurements

There are following types of measurements

           

           1. Primary measurements

           2. Secondary measurements

           3. Tertiary measurements

1.Primary measurements :-  

the measurement obtained directly by observation and compensation is called primary measurement. It needs no conversion, e.g.  measuring length , time, mass of a body etc.

2. Secondary measurements:-  

these measurement involve one conversion, e.g. measurement of pressure. In this pressure will be converted into a suitable form by a transducer and fed to the instrument.

   3.Tertiary measurements:- 

   the measurements  involve two conversion of the quantity under measurements, e.g. temperature measurement by thermo-couple , in this measurements the temp is first converted into voltage, which is again converted into the legible form through a meter.

Some important terminology

Important terms related to measurements are defined below:-

     

      1.  Instrument :-  

       

       Instrument is a device to measure value or magnitude of a quantity or a variable.

     

      2. True value :-  

       

      the true value of a quantity under measurement may be define as the average of an infinite no. of measured values when the deviation tends to zero”.

It is not possible to measure exact true value of the quantity

      

      3. Error :-  

      

       The difference b/w the “measured value” and “true value” of a quantity is called the error.

     4. Accuracy :- 

     

      Accuracy means “conformity to truth ‘ . the accuracy is the “closeness with which an instrument reading approaches the true value of the quantity being measured.

Accuracy = (measured value - true value ) / true value

Utilization Of Electrical Energy Qusestion

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Q1:- In case of travelling cranes, the motor preferred for boom hoist is 

1. slip ring induction motor 
2. squirrel cage induction motor 
3. synchronous motor 
4. speed phase motor 

ANSWER:- 1

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Q2:- The characteristics of dive for crane hoisting is 

1. smooth movement 
2. precise control 
3. fast speed control 
4. all of the above

ANSWER:-4

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Q3:- The capacity of a crane is expressed in terms of 

1. span 
2. types of drive
3. tonnes 
4. any of these 

ANSWER:-3

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Q4:- The travelling speed of cranes varies from 

1. 1 to 2.5 m/s 
2. 5 to 10 m/s 
3. 10 to 20 m/s 
4. 20 to 40 m/s 

ANSWER:-1

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Q5:- The advantage of a synchronous motor in addition to its constant speed is 

1. high power factor 
2. better efficiency 
3. lower cost 
4. all of the above 

ANSWER:-1

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Power Generation Questions

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Q1:- KVAR is equal to 

1. kW tan(fi)
2. kW sin(fi)
3. kVA cos (fi)
4. none of the above

ANSWER:- 1

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Q2:- Arc lamp operates at

1. low lagging p.f. 
2. high leading p.f. 
3. unity p.f. 
4. none of these 

ANSWER:-1

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Q3:- The maximum value of power factor can be 

1. 1
2. 0.9
3. 0.8
4. 0.7

ANSWER:-1

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Q4:- Power plant having maximum demand more than installed capacity will have uitilization factor

1. less than 100 %
2. equal to 100 %
3. more than 100 % 
4. none of these 

ANSWER:-3

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Q5:- The value of diversity factor is 

1. less than one 
2. greater than one 
3. equal to one
4. none of the above 

ANSWER:-2

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Utilization Of Electrical Energy Qusestion

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Q1:- In case of travelling cranes, the motor preferred for boom hoist is 

1. slip ring induction motor 
2. squirrel cage induction motor 
3. synchronous motor 
4. speed phase motor 

ANSWER:- 1

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Q2:- The characteristics of dive for crane hoisting is 

1. smooth movement 
2. precise control 
3. fast speed control 
4. all of the above

ANSWER:-4

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Q3:- The capacity of a crane is expressed in terms of 

1. span 
2. types of drive
3. tonnes 
4. any of these 

ANSWER:-3

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Q4:- The travelling speed of cranes varies from 

1. 1 to 2.5 m/s 
2. 5 to 10 m/s 
3. 10 to 20 m/s 
4. 20 to 40 m/s 

ANSWER:-1

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Q5:- The advantage of a synchronous motor in addition to its constant speed is 

1. high power factor 
2. better efficiency 
3. lower cost 
4. all of the above 

ANSWER:-1

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Lucknow Metro Questions

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Q1:- Zero adjustment becomes necessary in analog multimeter before measuring 

1. wattage 
2. current 
3. resistance
4. voltage

ANSWER:- 3

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Q2:- In the context of interconnected system which statement is correct 

1. increased the cost generation 
2. increased the service reliability
3. reduces the installed capacity 
4. decreases spinning reserve capacity 

ANSWER:-1

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Q3:- In dc generator eddy current loss is nothing but 

1. winding loss
2. iron loss 
3. friction loss 
4. copper loss

ANSWER:-2

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Q4:- The m/c which works on dynamically induced emf is 

1. transformer 
2. Dc motor 
3. inductance motor 
4. DC generator 

ANSWER:-4

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Q5:- Superposition theorem is used to obtain current in or voltage across any conductor of the 

1. magnetic network
2. linear network 
3. non linear network 
4. ac network 

ANSWER:-2

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Lucknow Metro Questins

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Q1:- O.C. test is performed on the transformer to determine 

1. core loss and non- load primary current 
2. total loss in the transformer
3. efficiency of the transformer
4. copper loss in the winding 

ANSWER:- 1

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Q2:- The direction of force on a current carrying conductor placed in a magnetic field can be found by using 

1. fleming's right hand rule 
2. cork screw rule 
3. fleming's left hand rule 
4. right hand thumb rule

ANSWER:-3

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Q3:- In extra high voltage line which of the following circuit breaker are most suitable 

1. air circuit breakers 
2. vaccum circuit breakers 
3. oil circuit breakers 
4. SF6 breakers 

ANSWER:-4

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Q4:- Resistance welding can not be used for 

1. dielectrics
2. non ferrous materials 
3. any metal 
4. ferrous materials 

ANSWER:-1

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Q5:- Transformer is static device which transfer

1. frequency from primary to secndary 
2. current from primary to secondary
3. voltage from primary to secondary 
4. power from pRimary to secodary

ANSWER:-4

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Lucknow Metro Questions

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Q1:- Buchholz relay is 

1. water actuated
2. gas actuated 
3. voltage actuated
4. current actuated

ANSWER:- 2

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Q2:- Differential relay protects  the device for following type of fault 

1. internal faults only 
2. depends on the setting of relays 
3. both internal and external faults 
4. external faults only 

ANSWER:-4

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Q3:- Choose the correct statement about ckt breakers

1. the making capability of circuit breaker should be root 2   times than breaking capability 
2. the making capability of circuit breaker should be 2.55   times than breaking capability 
3. the making capability of circuit breaker should be equal to breaking capability
4. the breaking capability of circuit breaker should be 2.55   times than making capability

ANSWER:-2

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Q4:- The function of economiser in thermal power plant is to 

1. extract heat from flue gases and uses it heating feed water to boiler
2. condense the steam exhasusted from turbine
3. remove carbon particles from flue gases.
4. increase temp of steam coming from boiler admitting to turbine

ANSWER:-1

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Q5:- In differential relay percentage bias is defined the ratio of 

1. difference of current in operating coil to the mean circulating current in restraning coil
2. mean current is restraining coils to the difference of current in operating coil
3. difference of current in restraining coils to the mean current in operating coil 
4. mean current in operating coil to the difference of current in restraning coils

ANSWER:-1

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Power Generation , transmission and distribution Questions

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Q1:- Which of the following plants will have the highest capital cost

1. Nuclear power plant 
2. Diesel power plant 
3. thermal power plant 
4. none of these

ANSWER:- 1

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Q2:- The pH value of water used for boiler is 

1. unity
2. 7 
3. 10 
4. slightly more than seven 

ANSWER:-4

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Q3:- Water is supplied to a boiler 

1. at 140 kg /sq cm 
2. at atmospheric pressure 
3. at sightly more than atmospheric pressure 
4. at more than the steam pressure in the boiler

ANSWER:-4

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Q4:- The MHD system generates 

1. a c only 
2. d c only 
3. a c and d c both 
4. either a c  or   d c 

ANSWER:-3

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Q5:- The oldest geothermal power plant is in

1. France 
2. Germany 
3. Italy
4. USA 

ANSWER:-3

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Lucknow Metro Questoions

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Q1:- In protection of transmission line against overvlotage due to lightning the lightning arrestor is connected b/w

1. transmission line conductor and earth 
2. transmission line conductor and primary bushing  of transformers
3. transmission line condutor 
4. transmission line condutor and overhead ground wires

ANSWER:- 1

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Q2:- Which motor is used whee high starting torque and wide speed range control is required 

1. 1- phase capacitor start motor
2. dc motor
3. induction motor
4. synchronous motor

ANSWER:-2

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Q3:- Overexcited synchronous motors are used for 

1. reducing the copper losses of inductive load
2. improving power factor of power systems with more inductive load 
3. reducing power factor of power system with more inductive load
4. maintaining the power factor to zero 

ANSWER:-2

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Q4:- The standard rating HP OF an Induction Motor is equivalent to 

1. 573.5 w
2. 374.5 w
3. 753.5 w
4. 735.5 w 

ANSWER:-4

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Q5:- Lighting arrestor is consists of 

1. a spark gap with non linear resistor
2. a spark gap in parallel non linear resistor
3. a spark gap in series with linear resistor 
4. a spark gap in parallel with linear resisitaor

ANSWER:-1

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Utilization of Electrical Engg.

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Q1:- The extra high voltage is according to Indian Electricity Rule

1. 440 Kv 
2. 66 kv 
3. 33 kv 
4. 110 kv 

ANSWER:- 1

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Q2:- Which locomotive has the highest operational duty ?

1. diesel 
2. electric 
3. steam 
4. all of these

ANSWER:- 2

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Q3:- which motor is used in tramways ?

1. AC single phase capacitor start motor 
2. AC three phase motor 
3. DC series motor 
4. Dc shunt motor 

ANSWER:- 3

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Q4:- overload capacity of diesel engines is usually restricted to 

1. 1 %
2. 10 %
3. 25 %
4. 50 %

ANSWER:- 2

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Q5:- Danger 440 v plates are 

1. danger notices 
2. caution notices 
3. advisory notices 
4. informal notices

ANSWER:- 2

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Utilization of Electrical Energy

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Q1:- Overall efficiency of streams locomotive system is close to 

1. 5 to 10 %
2. 75 to 30 %
3. 55 to 60 %
4. 25 to 30 %

ANSWER:- 1

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Q2:- In a steam locomotive electric power is provided through 

1. battery system
2. diesel engine generator 
3. overhead wire 
4. small turbo generator

ANSWER:-4

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Q3:- Maximum horse power of steam locomotive is 

1. 100 hp
2. 500 hp
3. 1500 hp
4. 2500hp

ANSWER:-3

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Q4:- The pressure of steam in a locomotive is 

1. 20 -30 kg/ sq cm 
2. 40 - 50 kg /sq cm
3. 10 - 15 kg sq cm 
4. 80 - 90 kg / sq cm 

ANSWER:-3

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Q5:- The efficiency of diesel locomotives is nearly 

1. 20 - 25 %
2. 35 - 40 %
3. 50 - 55 %
4. 70 - 75 %

ANSWER:-1

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Utiization Of Electrical Engg. Theory

Lumen:-

•  Lumen  is defined as the amount of luminous flux given out in space represented by one unit of solid angle by a source having an intensity of one candle in all directions.

                             lumen = candle power * solid angle 

total lumens given out by the source of one candle is 4 pi lumens.

Candle power :-

•  candle power is the light falls upon any surface, the phenomenon is called the illumination. it is defined as the number of lumens, falling on the surface per unit area. 
• it is denoted by symbol  E and is measured in lumen per square metre or lux candle.
• if a flux of F lumens falls on a surface of area A then the illumination of that surface is    E= F/A lumens / sq. m or lux 
• bigger unit of illumination is phot. 
• 1 phot =10 ^4  lux 

Metre candle :- 

•  it is also known as lux .
• it is the unit of illumination and is defined as the luminous flux falling per sq. meter on the surface which is everywhere perpendicular to the rays of light from a source of one Candle Power and one meter away from it.  Or it is the illumination produced by a source of one candle power on the inner surface of a sphere of a sphere of one meter radius.  

Centimetre Candle :-

• it is also a unit of illumination and is defined as the luminous flux falling per sq cm on the surface which everywhere is perpendicular to the rays of light from a source of one candle power and one cm away from it 

To be continue........ in next post 

SSC Jr. Engg. Questions

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Q1:- Motor used for elevators is generally 

1. sysnchronous motor
2. induction motor
3. capacitor start single phase induction motor 
4. any of these

ANSWER:-2

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Q2:- In case of contactors the contacts are generally made of 

1. copper
2. silver
3. cadmium copper 
4. any of these

ANSWER:-4

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Q3:- Which electromagnet is preferred for noiseless operation ?

1. DC operated 
2. AC operated 
3. any of these 
4. none of the above

ANSWER:-1

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Q4:-Long distance railways use 

1. 220 v DC
2. 25 kv , single phase AC
3. 25 kv ,  two phase - AC
4. 25 kv , three phase - AC

ANSWER:-2

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Q5:- Suburban railways use 

1. 1500 v , DC
2. 440 v three phase AC
3. 660 v three phase AC
4. 3.3 v three phase AC

ANSWER:-1

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Utilization of Eectrical Engg Theory

Light:-  

• light is defined as the radiant energy a hot body causing visual sensation on the human eye .

Flux:- 

• it is also known as luminous flux. 
• it is defined as the total quantity of light energy radiated or emitted per second from a luminous body in the form of light waves. 
• it is measured in lumens and is denoted by F .
• it is defined as the rate of uminous energy.
• if the lumens - hour is the luminous o/p of source of light and energy radiated for t hours, then flux is                                                                     F=Q/t

 Light Energy:-

• it is the energy contained in visual radiations in a given time and is expressed in lumen- hour and is denoted by Q

Luminous Efficiency or Radiant Efficiency :- 

• it is defined as the o/p in lumens per watt of the power consumed by the source of light. it is measured in lumens per watt. 
• if a bulb is rated at 500 watt and 250 volts, has an efficiency of 13 lumens/watt. then total flux produced by bulb = 500 * 13  =6500 lumens 

Luminous Intensity:- 

• luminous intensity in any particuar direction is the luminous flux emitted by per unit solid angle by a point sopurce and is denoted by I.                                                                                                      I=F/w   lumens/ steradian or Candle 
• it is the ratio of the brightness of a source of light to that of standard candle. 
• one candle gives out luminous flux of 4 pi lumens in space.
• Thus lumens emitted by one candle source of light is one lumen/steradian.

•    In scientific terms, candle is defined as the luminous intensity in the perpendicular direction of a surface os 1/600,000 sq meter of a full radiator at the temp of freezing platinum under a pressure of 101,325 N/sq. meter.

To Be Continue..........in next slide .......

Lucknow Metro Question

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Q1:- Function of surge absorber is 

1. to protect apparatus under short circuit fault
2. exactly same as lighting arrestor
3. to divert surge to earth 
4. to reduce the steepness of wave front of a surge 

ANSWER:- 4

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Q2:- The rotor of an I.M. rotates due to 

1. interaction b/w the stator magnetic field and field due to induction current in the rotor 
2. interaction b/w the stator voltage and rotor voltage 
3. p[rime mover connected to the motor 
4. interaction b/w the i/p supply frequency and rotor voltage frequency 

ANSWER:-1

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Q3:- The resistance R offered by a conductor varies 

1. directly as its cross sectional area and the resistivity of the material and inversely as its length 
2. directly as its length and cross sectional area of the material and inversely a sits resistivity 
3. directly as its resistivity and length of the material and inversely as its cross sectional area 
4. directly as the temperature and cross sectional area of the material and inversely as its length 

ANSWER:-3

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Q4:- Safety factor of insulator is the ratio of 

1. puncture strength to flash over voltage 
2. flash over voltage to puncture strength 
3. flash over voltage to line voltage 
4. line voltage to flash over voltage 

ANSWER:-1

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Q5:- Power factor can be improved by 

1. static capacitor 
2. synchronous condenser
3. phase advancers 
4. all of the above 

ANSWER:-4

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Lucknow Metro Questions

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Q1:- Bulk oil circuit breakers are suitable for 

1. low voltage systems 
2. high voltage systems
3. medium voltage systems
4. extra high voltage system 

ANSWER:- 1

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Q2:- Which of the following is symmetrical fault ?

1. three phase short circuits 
2. three phase short circuit with different fault impedance 
3. line to line fault 
4. line to ground fault 

ANSWER:-1

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Q3:- Four lamps of 100 watt each are connected in parallel to 240 volt supply . the equivalent resistance of the circuit will be 

1. 300 ohm 
2. 33.33 ohm 
3. 1728 ohm 
4. 192 ohm 

ANSWER:-4

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Q4:- When AC voltage is applied across pure resistance pure inductor and pure capacitor separately the true statement is 

1. V&I are in phase for inductor, V leads I for resistance & I leads V for capacitor 
2. V&I are in phase for resistor V leads I for capacitor & I leads V for inductor 
3. V&I are in phase for resistor , V leads I for inductor & I leads V for for capacitor 
4. V&I are in phase for capacitor ,V leads I for inductor &
   I leads V for resistor 

ANSWER:-3

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Q5:- In RLC series circuit with constant voltage source but of frequency varaying from zero to infinity . the ckt is said to be in electrical reasonace when 

1. magnitude of inductance =capacitance and Z is not equal to R
2. magnitude of inductance = capacitance and Z=R
3. magnitude of inductance > capacitance and Z is not equal to R
4. magnitude of inductance < capacitance and Z is not equal to R

ANSWER:-2

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Switchgear And protection

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Q1:- In electrical fault can be caused by 

1. insulation faliure 
2. mechanical faliure
3. both 1 and 2 
4. none of the above 

ANSWER:- 3

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Q2:- Type of faults are

1. symmetrical faults
2. assymmetrical faults
3. both 1 and 2 
4. none of the above

ANSWER:-3

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Q3:- In case of short circuit conditions 

1. low current is flow 
2. high current is flow
3. least current is flow
4. none 

ANSWER:-2

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Q4:- In case of open circuit conditions

1. current is high
2. current is low
3. zero current flow
4. none of the above

ANSWER:-3

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Q5:- In fault condition which of the following is true

1. impedance is low and fault currents are large
2. impedance is high and fault currents are large
3. impedance is low and fault currents are low
4. none of the above

ANSWER:-1

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