The document provides information about various components and aspects of electrical substations: 1) Stones are used in substations to drain oil from transformers if leaks occur and to prevent weed growth. Devices like synchronous condensers and reactors are used to improve power factor. 2) Minimum phase to phase clearances for 400kV conductors and common components like CVTs, wave traps, and arrestors are identified. Reactors are used to limit short circuit current. 3) Ring main distribution systems are generally used for distribution. Earthing conductivity is affected by various soil factors and emulsifier protection relates to multiple protections like grounding and fire.

1. Stones are provided in the substation to:
a) To avoid fire accident by draining oil from transformer if leaks
b) To avoid growing of weeds and plants
c) To provide insulation
d) All the above D
In order to improve the power factor ___ device is employed in the substation
a) Synchronous condenser
b) Synchronous reactor
c) Series Capacitors
d) None of the above A
What is the minimum phase to phase clearance required for 400kV conductors in substation:
a) 3500 mm b) 4200 mm c) 5000 mm d) 4500 mm B
In substation which of the device is a carrier communication device:
a) CVT
b) Earth conductor
c) Wave trap
d) Lightning arrestor C
Which of the device is employed in substation to limit the short circuit current in the power
system:
a) Shunt condenser b) Reactor c) Series capacitor
d) Shunt capacitor B
Which of the following busbar arrangement is generally employed in distribution system:
a) One-and-half breaker arrangement
b) Main and transfer arrangement
c) Ring main distribution system
d) Single busbar arrangement system C
Earthing conductivity is affected by:
a) Moisture content in the soil b) Chemical composition
c) Concentration of salts in the soil d) All the above D
Emulsifier protection is associated with:
a) Grounding protection
b) Dielectric strength protection of cables and conductors
c) Lightning protection
d) Fire protection D
The size of Gas Insulated Substation is significantly small compared to conventional
substation because:
a) High electronegative property of SF6 gas
b) High dielectric property of SF6 gas
c) High Insulation property of SF6 gas
d) All the above D
What is Marshalling Kiosk in power transformer:
a) It provides alarms, trips, controls and indications from main transformer
b) It is the base on which transformer rail is provided to pull and push transformer
c) It is the pressure device ruptures when temperature inside transformer increases
d) None of the above A

2. Which is the first equipment seen in the substation while coming from transmission system:
a) Circuit breaker b) Lightning arrester c) Current transformer
d) Transformer B
Gas Insulated Substation is employed where:
a) Where there is less space available b) For high altitude substations
c) In terrain region d) All the above A
A bus coupler circuit breaker is utilized in a substation for:
a) Joining the transmission line with station bus-bar
b) Joining main and transfer bus in a substation
c) Joining the generator with transfer
d) Joining the neutral of the generator with earth B
Which of the gas is used in gas insulated substation:
a) Nitrogen + SF6
b) Hydrogen + SF6
c) SF6
d) None of the above C
Which of the following bus-bars arrangement is more reliable and flexible:
a) Main and transfer bus scheme
b) One-and-half breaker scheme
c) Double main busbar scheme
d) Single busbar scheme B
What is the maximum transmission voltage substation in India:
a) 400 kV b) 500 kV c) 750 kV d) 1000 kV C
A busbar is rated by:
a) Current only b) Voltage only c) Current, voltage and frequency
d) Current, voltage, frequency and short circuit current D
In a substation current transformers are used to:
a) Measuring purpose b) Protection purpose connecting to relays
c) Both (a) and (b) d) None of the above C
Step potential and Touch potential is associated with:
a) High voltage transmission
b) Earthing of the substation
c) Voltage rise in the substation
d) Communication systems B
It is the minimum clearance required between the live conductors and maintenance operators
limit:
a) Ground clearance b) Phase clearance c) Sectional clearance
d) None of the above C
When is the Ferranti effect on long overhead lines experienced?
a) The lines are lightly loaded
b) The lines are heavily loaded
c) The lines are fully loaded
d) The power factor is unity A
What is the surge impedance loading of a lossless 400kV, 3 phase, 50Hz overhead line of
average of surge impedance of 400 ohms?

3. a) 400MW
b) 400 X (3)1/2
MW
c) 400 / (3)1/2
d) 400 KW A
In a 7/30 ACSR conductor why is grease put between steel and aluminium conductors?
a) To reduce corrosion by electrolytic action between zinc (galvanising agent on steel) and
aluminium
b) To reduce friction between the strands
c) To reduce leakage of current from the aluminium strands to steel strands
d) To eliminate air pockets A
A travelling wave due to lightning with an incident voltage V travels through the overhead
line of surge impedance of 400 ohms and enters a cable of surge impedance of 40 ohms.
What is the voltage entering the cable at the junction
a) V/11
b) 4V/11
c) 2V/11
d) V C
Bundled Conductors are used for EHV transmission lines primarily for reducing
a) Corona Loss b) Surge Impedance of the line
c) Voltage drop across the line d) I2
R loss A
If the traveling wave which is traveling along the loss free line which doesnot undergone any
reflection after it reached the end, then the end of the line is:
a) Short circuited b) Open Circuited c) Terminated with inductor
d) Terminated in to a resistance which is equal to the Surge Impedance of the line C
A travelling wave 400/1/50 means crest value of:
a) 400kV with rise time of 1/50 s
b) 400kV with rise time 1 s and fall time 50 s
c) 400kV with rise time 1 miro sec with fall time 50 micro sec
d) 400MV with rise time 1 micro sec and fall time 50 micro sec C
Consider the following statements:
Surge Impedance loading of a transmission line can be increased by
1. Increasing its voltage level
2. Addition of lumped inductance in parallel
3. Addition of lumped capacitance in series
4. Reducing the length of the line
of the following statements
a) 1 and 3 are correct b) 1 and 4 are correct c) 2 and 4 are correct
d) 3 and 4 are correct A
Transmission efficiency of transmission line increases with the:
a) Decrease in power factor and voltage
b) Increases in power factor and voltage
c) Increase in power factor and decrease in voltage
d) Increase in the voltage but decrease in the power factor B
Constant power locus of transmission line at particular sending end and receiving end voltage
is:
a) A straight line b) A circle c) A parabola d) An ellipse B

4. Relay contacts are normally made up of:
a) Silver contacts b) Copper contacts c) Aluminium contacts
d) Lead contacts A
The most efficient torque-producing actuating structure for induction type relays is:
a)Shaded pole structure b) Watt-hour meter structure
c) Induction cup structure d) Single induction cup structure C
Impedance relays can be used for:
a) Phase faults only
b) Earth faults only
c) Both earth and phase faults
d) None of the above C
Sparking between the contacts can be reduced by inserting:
a) A capacitor in parallel with the contacts
b) A capacitor in series with the contacts
c) A resistor in the line
d) A reactor in the line A
The contact resistance is least affected by:
a) Shape of the contact faces
b) Ambient temperature
c) Mechanical forces applied
d) Amount of surface commutation B
The arc voltage produced in an ac circuit breaker is always:
a) In phase with the arc current
b) Lagging the arc current by 90 deg
c) Leading the arc current by 90 deg
d) In phase opposition with the arc current A
Breaking capacity of the circuit breaker is usually expressed in:
a) MVA b) MW c) Kilo-amperes d) kV A
Which of the following circuit breakers produce least arc energy:
a) Plain oil b) Minimum oil c) Air blast d) Air break C
Arc chutes are used in:
a) Oil circuit breaker b) Vacuum circuit breakers
c) SF6 circuit breakers d) Air blast circuit breakers D
A thermal protection switch is used to provide protection against:
a) Over load b) Temperature c) Short circuit
d) Over voltage A
Mho relay have an R-X characteristics depicted by:
a) A straight line passing through origin
b) A straight line parallel to X-axis
c) A straight line parallel to R-axis
d) A circle passing through the origin D
Any winding of a power transformer develops short circuit owing to:
a) Loose connections b) Insulation failure
c) Impulse voltage d) Mechanical vibration C

5. The relay used for the feeder protection is:
a) Under-voltage relay b) Translay relay
c) Thermal relay d) Buchholz relay B
The relay best suited for phase fault relaying for medium transmission lines is:
a) Mho relay
b) Reactance relay
c) Impedance relay
d) None of the above C
For ground fault, which of the relay is preferred:
a) Plain impedance relay b) Directional relay
c) Reactance relay d) Over-current relay C
The short circuit current of an alternator, in case of line to line fault depends on its:
a) Short circuit resistance b) Transient reactance
c) Synchronous reactance d) None of the above C
Solid earthing is provided for the voltage below:
a) 100 kV b) 600 V c) 11 kV d) 66 kV B
A lightning arrester connected between the line and earth in a power system
a) Protects the terminal equipment against travelling surges
b) Protects the terminal equipment against lightning strokes
c) Suppresses the high frequency oscillations in the line
d) Reflects back the travelling waves approaching it A
Thermal relays are used for the protection of motors against over-current owing to:
a) Short circuit b) Heavy loads c) Earth fault d) All the above B
Buchholz relay is:
a) Located in the conservator tank
b) Located in the transformer tank itself
c) Connected in the pipe connecting main tank of transformer and conservator
d) Installed in the circuit breaker C
Isolators are used for disconnecting a circuit when:
a) Line is energised
b) Line is on full load
c) Line carries no current
d) Can be operated under any condition C
Under-voltage relay is mostly used for:
a) Transformer protection b) Bus-bar protection
c) Motor protection d) Feeder protection C
Earth fault relays are:
a) Directional relay b) Non-directional relay c) Short operate time relay
d) Under voltage relay A
Differential relays are used for the protection of equipments against:
a) Internal faults b) Over-current c) Reverse current d) Reverse power A
Admittance relay is:
a) Non-directional relay b) Directional relay c) Differential relay
d) None of the above B

6. The torque developed in Induction type relay is:
a) Directly proportional to the current
b) Directly proportional to the square of the current
c) Directly proportional to square root of the current
d) Inversely proportional to the current B
Buchholz relay is a:
a) Oil actuating relay b) Current actuating relay c) Gas actuating relay
d) Oil temperature-actuating relay C
The relay with inverse time characteristics will operate within:
a) 10 msec b) 5 to 10 sec c) 10 to 20 sec d) above 25 sec B
The operation speed of a relay depends on:
a) Rate of flux buildup b) Armature core air gap c) Spring tension
d) All the above D
Which of the following relays has inherent directional characteristics:
a) Mho relay b) Impedance relay c) Reactance relay d) Distance relay A
The rating of the Transformer __ when the supply frequency is increased:
a) Remains unchanged b) Increases c) Decreases d) None of the above B
Distortion of the whole core and subsequent damage to the coil insulation due to intense eddy
currents may be caused due to the failure of:
a) Insulation of the winding
b) Insulation between the laminations
c) Insulation between the core and damping bolts
d) Both (a) and (b) D
Booster transformer should never:
a) Have fuse in the HV winding
b) Be left open circuited
c) Be left closed circuited
d) None of the above C
In a transformer, with closed magnetic coupling between primary and secondary __ will
improve:
a) Efficiency
b) All day efficiency
c) Regulation
d) None of the above C
Zero sequence currents can flow from a line into a transformer bank if the windings are:
a) Grounded star/delta
b) Delta/star
c) Star/Star grounded
d) Delta/Delta C
An auto transformer is preferred over an ordinary two winding transformer due to:
a) Safety of operation
b) Availability of taps on secondary
c) Copper savings
d) All the above C

7. The harmonic currents in a power transformer does not cause increase in:
a) Secondary voltage
b) Core loss
c) Copper loss
d) Magnetic interference with protective relays A
In conversion of 3-phase to 2-phase supply with T connection, the transformation ratio of the
teaser will be__ times to that of main transformer:
a) 1.732
b) 1.15
c) 0.866
d) Unity C
Two transformers of identical voltages but different capacities are operated in parallel, for
satisfactory load sharing:
a) Impedances should be equal
b) Per unit impedance must be equal
c) per unit impedance and X/R ratio must be equal
d) Impedance and X/R ratio must be equal C
A shell type transformer is commonly used as it has:
a) Two magnetic paths
b) Reduced magnetic flux leakage
c) Reduced copper loss
d) Both (a) and (b) D
The color of fresh dielectric oil used in the transformer is:
a) Dark brown
b) Pale yellow
c) Pale pink
d) White grey B
The thickness of transformer core laminations is:
a) 3mm to 5mm
b) 0.35mm to 0.5mm
c) 30mm to 50 mm
d) 0.035mm to 0.05mm B
For transformers employing CRGO, the area of the yoke is taken __ of the core:
a) 80 to 85%
b) 115 to 125%
c) Equal to
d) Half B
The core used in high frequency transformer is __ core:
a) Aluminium
b) Ferrite
c) Carbon
d) Iron B
In order to reduce the hysteresis loss:
a) Core may be laminated
b) Silica steel may be used as the core
c) Core may be constructed with magnetic materials such as ALNICO
d) Core may be impregnated with varnish D

8. Which of the following will improve the mutual coupling between primary and secondary
circuits:
a) Transformer oil of high breakdown voltage
b) High reluctance magnetic core
c) Winding material of high resistivity
d) Low reluctance magnetic core D
The magnetic properties of silicon steel crystal are best along the:
a) Cube diagonals
b) Cube edges
c) Surface diagnals
d) None of the above B
Transformer core is made of:
a) Silicon sheet steel
b) Chromel steel
c) Low carbon steel
d) High content silicon steel A
Which of the following statements associated with the Buchholz relay is not true:
a) It is a voltage sensitive device
b) It is used only on oil cooled transformers
c) It is not provided on transformers of the rating below 500kVA
d) Its operating time is of the order of 0.1 seconds A
With stepping in construction of the transformer core:
a) Core losses are reduced
b) Copper losses are saved
c) Mechanical strength of the core is improved
d) Both (a) and (b) D
A distribution transformer is required to supply:
a) Variable load between no load to full load
b) Constant part full load throughout the day
c) Constant full load through out the day
d) Variable load between no load to full load at a fixed power factor A
In a Delta -Delta connection, if one of the transformer winding is open, the capacity will
reduce to:
a) 66.67%
b) 57.74%
c) 50%
d) 33.33% B
A 3-phase transformer over a bank of 3-single phase transformers of equal rating, has the
advantage of:
a) Low cost
b) Less weight
c) Occupation of less space
d) All the above D
In which of the transformer, the tertiary winding is used:
a) Star-delta
b) Delta-delta
c) Star-star
d) Delta-star C

9. The magnetizing current in a transformer is rich in:
a) 3rd harmonic
b) 5th harmonic
c) 7th harmonic
d) 11th harmonic A
Scott connections are used for:
a) Single phase to three phase transformation
b) Three phase to single phase transformation
c) Three phase to two phase transformation
d) Any of the above C
For successful parallel operation of two single phase transformers, the most essential
condition is that their:
a) Percentage impedances are equal
b) Polarities are properly connected
c) Turn-ratios are exactly equal
d) kVA ratings are equal B
Maximum transient currents flow through the transformer winding when when it is switched
on with its secondary winding ___ circuited and when the input voltage wave passing through
the __ value
a) Open, zero
b) Short, zero
c) Open, maximum
d) Short, maximum A
Tappings of a transformer are provided:
a) At the phase end of the LV side
b) At the phase end of the HV side
c) At the neutral end of the HV side
d) At the middle of the HV side D
The excessive temperature rise in the Transformer causes maximum damage to:
a) Winding insulation
b) Core laminations
c) Copper wining
d) Dielectric strength of the oil A
Which of the following 3-phase connection of a transformer causes interference with
the neighboring communication lines:
a) Delta-star
b) Star-delta
c) Star-star
d) Delta-star C
Power transformers are provided with additional cooling arrangement in order to:
a) Increase the power rating
b) Increase insulation life
c) Lower operating temperature
d) All the above D
A Distribution transformer is selected on the basis of:
a) Voltage regulation

10. b) Efficiency
c) All day efficiency
d) All the above C
The winding used in 3-phase shell type transformer is __ type:
a) Circular
b) Cylindrical
c) Sandwitch
d) Rectangular C
Five limb core construction is preferred over three limb construction as in this type of
construction:
a) Hysteresis loss is reduced
b) Eddy current loss is reduced
c) Magnetic reluctance of the three phases can be balanced
d) Copper losses can be reduced C
The most common method of cooling employed in power transformer is:
a) Oil natural
b) Natural cooling
c) Air cooling
d) Air-blast cooling A
In large power transformer, best utilization of available core space can be made by
employing __ cross section
a) Rectangular
b) Square
c) Stepped
d) None of the above C
The distribution transformer is designed with minimum possible core losses. This is
because:
a) The primary of the distribution transformer is energized for all 24 hours
b) Iron losses will cause undue heating
c) Iron losses may cause damage to the insulation
d) All the above A
Which of the following transformer connection will give highest secondary voltage:
a) Delta primary, delta secondary
b) Delta primary, star secondary
c) Star primary, delta secondary
d) Star primary, star secondary B
The chemical used in the breather is:
a) Sodium chloride
b) Silica sand
c) Silica gel
d) Copper silicate gel C
Major insulation in a transformer is the insulation between the:
a) LV wining and core
b) LV winding and HV winding
c) Turns of the windings
d) Both (a) and (b) D

11. Low voltage winding is placed next to the core in the case of concentric windings as
__ is reduced:
a) Hysteresis loss
b) Leakage fluxes
c) Eddy current loss
d) Insulation requirement D
The transformer oil should have:
a) High volatility
b) High viscosity
c) High dielectric strength
d) All the above C
The Transformer core laminations are insulated from each other by:
a) Paper
b) Thin varnish coating
c) Mica strip
d) All the above can be used for insulation B
For minimum weight of the transformer, the iron weight should be __ the weight of
the copper:
a) More than
b) Equal to
c) Less than
d) None of the above B
The iron loss in a 100 kVA transformer is 1 kW and the full load copper losses are 2 kW, then
the maximum efficiency occurs at a load of:
a) 141.4 kva
b) 70.7 kva
c) 50 kva
d) 70.7 kw
In a transformer, iron core is provided in order to:
a) Reduce the magnetic path reluctance
b) Reduce eddy current and hysteresis losses
c) providing the coupling between primary and secondary winding
d) Increase the magnetizing current
The transformer efficiency under heavy loads is comparitively low due to:
a) Large increase in copper losses
b) Drop in the power factor drastically
c) Both (a) and (b)
d) None of the above
In a transformer:
a) Both open circuit (O.C) and short circuit (S.C) tests are conducted on LV side
b) open circuit (O.C) test is conducted on LV side and Short Circuit (S.C) test is conducted on
HV side
c) open circuit (O.C) test is conducted on HV side and Short Circuit (S.C) test is conducted on
LV side
d) Both open circuit (O.C) test and Short Circuit (S.C) test are conducted on HV side

12. The size of the transformer core depends on the:
a) Frequency
b) Permissible flux density in the core
c) Area of the core
d) All the above
Distribution transformers are designed to have maximum efficiency at:
a) At full load
b) Half load
c) No load
d) At almost 80% of the laod
The use of high flux density in the design of the transformer:
a) Reduces the eddy current losses
b) Reduces the weigh per kva output
c) Reduces the copper loss
d) Distorts the sinusoidal wave shape phenomenon
Natural air cooling is used for the transformers of the rating upto:
a) 100 kva
b) 500 kva
c) 5-10 kva
d) 1 MVA
Positive regulation of the transformer is indication of ___ load
a) Inductive
b) Capacitive
c) Either inductive or capacitive
d) Resistive
A transformer is supplying pure resistive (unity power factor) load. The power factor of the
transformer will be:
a) about 0.95 (lead)
b) about 0.95 (lag)
c) unity
d) 0.8
During short circuit the core losses are negligible because:
a) The voltage applied across the high voltage side is fraction of the rated volage
b) The current on the low voltage side is very small
c) the power factor is almost zero
d) Iron becomes saturated
The open circuit test of the transformer gives information related to:
a) magnetizing current
b) core loss
c) both magnetizing current and core loss
d) None of the above
If the thickness of the laminations used in the transformer core are increased. Then which
losses will increase:

13. a) eddy current
b) hysteresis
c) copper loss
d) both a and b
The losses which vary with variation in the load are:
a) Hysteresis loss
b) copper losses
c) eddy current losses
d) All the above
The desirable properties of transformer core are:
a) Low permeability and low hysteresis loss
b) High permeability and low hysteresis loss
c) Low permeability and high hysteresis loss
d) High permeability and high hysteresis loss
The all day efficiency of the transformer is applicable to:
a) Power transformer
b) Distribution transformer
c) Auto transformer
d) Only (a) and (b)
The joints of the transformer core lamination are staggered so as to:
a) Avoid continuous gap causing increase in the magnetising current
b) To increase the mechanical strenght of the core
c) Avoid undue humming noise
d) All the above
In order to reduce hysteresis loss:
a) Core may be laminated
b) Silicon steel may be used as the core material
c) Core may be constructed with any permanent magnetic material
d) Core may be impregnated with varnish
Silicon content in iron laminations is kept within 5% as it:
a) Increases the hysteresis loss
b) Increase the hysteresis loss
c) Makes the material brittle
d) Reduces the curie point
Conservator is employed to:
a) Takes care about the expansion and contraction of oil
b) Provides fresh air for increasing cooling effect
c) Stores extra oil in case of emergency
d) Provides fresh air for increasing cooling effectively
Multi step core is used in a transformer to:
a) Increase the output
b) Decrease the cost of the core material

14. c) Decrease the cost of the cooper
d) increase the efficiency
In a power transformer:
a) Primary winding is always wound with many windings of thin wire
b) Secondary windings are always wound with lesser number of turns of thin wire
c) Low voltage winding is always wound with lesser number of turns of thicker wire
d) High voltage winding is always wound with larger number of turns of thicker wire
Grain oriented laminated sheet steel in transformer reduces:
a) Copper loss
b) Eddy current loss
c) Hysteresis loss
d) Both b and c
The hum in a transformer is mainly attributed to:
a) Variations in the load
b) Mechanical vibrations
c) Magentostriction
d) both b and c
The thickness of the transformer core laminations is:
a) 3 mm to 5 mm
b) 0.35 mm to 0.5 mm
c) 30 mm to 50 mm
d) 0.035 mm to 0.05 mm
The all day efficiency of the distribution transformer is defined as the ratio of:
a) Power output to power input in kw during the whole day
b) Energy output to energy input in kwh during the whole day
c) kva output to kva input during whole day
d) kvah output to kvah input during the whole day
If the supply frequency of the transformer is doubled:
a) Hysteresis loss also doubles
b) eddy current loss also doubles
c) iron loss doubles
d) copper loss double
Open circuit test in the transformer is performed with:
a) Rated transformer voltage
b) Rated transformer current
c) direct current
d) High frequency supply
The mutual flux in a loaded transformer can be varied by:
a) Primary current
b) Load Impedance
c)Secondary current
d) Reluctance of the magnetic path

15. In a transformer __ decreases with increase in the leakage flux
a) Primary induced emf
b) Secondary Induced emf
c) Secondary terminal voltage
d) none of the above
The power factor of the power transformer on no load will be about:
a) unity
b) 0.75
c) 0.5
d) 0.35
The flux in the transformer core:
a) Increases with increase in load
b) Decreases with increase in load
c) Remain constant
d)It depends on the type of load (inductive or capacitive)
In a transformer circuit mode, the core loss is represented as a
a) Series resistance
b) Series inductance
c) Shunt resistance
d) Shunt inductance
The transformer has zero regulation at:
a) Zero power factor
b) unity power factor
c) lagging power factor
d) leading power factor
The value of the flux involved in the emf equation for a transformer is:
a) Instantaneous
b) Maximum
c) Average
d) rms
In a transformer operating at constant voltage if the input frequency increases, the
core loss:
a) Increases
b) Decreases
c) Remain constant
d) Increases as square of the frequency
If the dc voltage is applied instead of ac voltage to the primary side of a transformer:
a) Secondary side will burn
b) Primary side will burn
c) Secondary voltage will be equal to primary voltage
d) No secondary voltage is induced
The flux created by the current flowing through the primary winding induces emf in:
a) Primary winding only
b) Secondary winding only

16. c) both primary and secondary winding
d) None of the above
The emf induced in the primary
a) is in phase with the flux
b) lags behind the flux by 90
c) leads the flux by 90
d) it is in phase opposition to that of the flux
Total emf induced in the primary winding is due to:
a) mutual flux only
b) leakage flux only
c) both mutual flux and leakage flux
d) mutual flux minus leakage flux
The power factor of the transformer on no load is poor due to
a) Magnetising reactance of the transformer
b) Open-circuited secondary
c) Low primary winding resistance
d) Low no load current A
The no load current of the transformer lags behind the applied voltage by:
a)90o
b)0
c)75o
d) 135o
A