faculty of degree engineering - 083 - dr. subhash technical

Faculty of Degree Engineering - 083 Department of EC / Electrical Engineering -09

MCQ AND SHORT QUESTION BANK

Dr. Subhash Technical Campus- The Jewel of Junagadh

Subject: - POWER SYSTEM - 1 Subject code: - 3140914

Chapter 1. Conventional generation, load curves and tariffs

1.Fill in the blanks by inserting appropriate words/figures :

(i) The major heat loss in a steam power station occurs in........

(ii) The thermal efficiency of a steam power station is about........

(iii) Cooling towers are used where........

(iv) The running cost of medium power stations is about..............paisa per unit.

(v) In a hydro-electric plant, spillways are used........

(vi) The running cost of a hydro-electric plant is about............paise per unit.

(vii) For high head hydro-electric plants, the turbine used is ........

(viii) Francis and Kaplan turbines are used for.............heads.

(ix) Surge tank is provided for the protection of........

(x) Of all the plants, minimum quantity of fuel is required in.......plant.

2. Pick up the correct words from the brackets and fill in the blanks:

(i)The cost of fuel transportation is minimum in...........plant.

A. steam power,

B. hydro-electric,

C. nuclear power




(ii)The cheapest plant in operation and maintenance is............plant.

A. diesel power

B. hydro-electric

C. steam power

(iii)Economizers are used to heat ........

A. air

B. feed water

C. steam

(iv)The running cost of a nuclear power plant is about ........ paise per unit.

A. 20

B. 48

C. 64

(v)Diesel power plants are used as ........ plants.

A. base load

B. standby

(vi)India’s first nuclear power plant was built at

A. Tarapur

B. Rana Partap Sagar

C. Kalpakkam

(vii)The most simple and clean plant is ........ plant

A. steam power

B. hydro-electric

C. nuclear power




(viii)The first nuclear power plant in the world was commissioned in

A. U.S.A

B. U.S.S.R

C. England

(ix)Gas turbine power plant is ........ efficient than steam power plant

A. more

B. less

(x)Draft tube is used in........ Turbines.

A. impulse

B. reaction

ans

1.(i) Condenser, about 53% (ii) 28% (iii) water is not available in sufficient quantity (iv) 15 (v)

to discharge surplus water on the downstream side of dam (vi) 5 (vii) pelton wheel (viii)

medium and low (ix) penstock (x) nuclear power.

2.(i) Hydro-electric (ii) hydro-electric (iii) feed water (iv) 20 (v) standby (vi) Tarapur (vii)

hydro-electric (viii) U.S.S.R. in 1954 (ix) more (x) reaction.

Thermal power plant mcq

1. In steam power plant which of the following component needs more maintenance:

a) Condenser

b) Boiler

c) Turbine

d) Coal carrying system

B




2. The pH value of the water used in boiler is:

a) unity

b) 7

c)slightly less than seven

d) slightly more than seven

D

3. For the flue gas flow, tick the correct sequence:

a) Boiler-Air preheater- economizer- ID fan- Chimney

b) Boiler- ID fan -Air preheater- Economizer- Chimney

c) Boiler- Economizer- Air preheater- ID fan- Chimney

d) None of the above

C

4. Hydrogen cooling employed in large thermal power plant alternator:

a) Increases the insulation life

b) Decreases the insulation life

c) Does not effect the insulation life


A

5. Hydrogen cooling is employed in:

a) Turbo Generators only

b) Water wheel Generators only




c) Can b used in both turbo generators and water wheel generators

d) none of the above

A

6. The efficiency of the electro static precipitators will be of the order:

a) 99.6%

b) 90%

c) 85%

d) 80%

A

7. Economizer is normally employed when boiler pressure exceeds:

a) 70 kg/cm2

b) 50 kg/cm2

c) 30 kg/cm2

d) can be used for all pressures

A

8. The sizing of the generator in power plant is based on:

a) Current carrying capacity ratings only

b Insulation strength ratings only

c) Both (a) and (b)


C




9. With out Electro static precipitators:

a) ID fan rating should be increased

b) Economizer rating should be increased

c) Chimney height should be reduced


A

10. In thermal power plants the condenser used is of:

a) surface type

b) jet type

c) can be both surface type and jet type


A

8. The sizing of the generator in power plant is based on:

a) Current carrying capacity ratings only

b Insulation strength ratings only

c) Both (a) and (b)


C

9. With out Electro static precipitators:

a) ID fan rating should be increased

b) Economizer rating should be increased

c) Chimney height should be reduced

C




10. In thermal power plants the condenser used is of:

a) surface type

b) jet type

c) can be both surface type and jet type


A




Chapter 2. Introduction to wind and solar power generation

Solar power generation

1. The function of a solar collector is to convert.......

A.Solar Energy into Electricity

B.Solar Energy radiation

C.Solar Energy thermal energy

D.Solar Energy mechanical energy

2. Most of the solar radiation received on earth surface lies within the range of........

A.0.2 to 0.4 microns

B.0.38 to 0.78 microns

C.0 to 0.38 microns

D.0.5 to 0.8 microns

3. For satellite the source of energy is........

A.Cryogenic storage

B.Battery

C.Solar cell

D.Any of the above

4. Reflecting mirrors used for exploiting solar energy are called........

A.Mantle

B.Ponds

C.Diffusers

D.Heliostats




5. The output of solar cell is of the order of........

A.1 W

B.5 W

C.10 W

D.20 W

6. Flat plate collector absorbs.......

A.Direct radiation only

B.Diffuse radiation only

C.Direct and diffuse both

D.All of the above

7. A pyranometer is used for mesurement of.......

A.Direct radiation only

B.Diffuse radiation only

C.Direct as well as diffuse radiation

D.All of the above

8. Most widely used solar material is........

A.Arsenic

B.Cadmium

C.Silicon

D.Steel

9. Photovoltaic cell or solar cell converts........

A.Thermal energy into electricity

B.Electromagnetic radiation directly into electricity




C.Solar radiation into thermal energy

D.Solar radiation into kinetic energy

10. Temperature attained by a flat-plate collector is of the........

A.Order of about 900C

B.Range of 1000C to 1500C

C.Above 1500C

D.None of the above

11. The voltage of a single solar cell is.......

A.0.2 v

B.0.5 v

C.1.0 v

D.2.0 v

12. Solar cells,for power generation,entail the following major disadvantages........

A.Variable power

B.High cost

C.Lack of availability

D.Large area requirement

13. Thermionic converterutilizes........

A.Thermionic emission effect

B.Peltier effect

C.Seebeck effect

D.None of the above




14. Largest geothermal plant in operation is in........

A.Maxico

B.Italy

C.Russia

D.California

15. Bulb turbines are........turbines

A.Low head

B.High head

C.High speed

D.High pressure

16. How many planets are there in the Solar System?

A: 7

B: 8

C: 9

D: 10

17 What planet is closest to the sun?

A: Mars

B: Mercury

C: Earth

D: Venus

18 What is the second planet from the sun?

A: Mercury

B: Earth




C: Mars

D: Venus

19 What is the third planet from the sun?

A: Earth

B: Mars

C: Jupiter

D: Venus

20 What is the fourth planet from the sun?

A: Earth

B: Mars

C: Venus

D: Jupiter

21 What is the fifth planet from the sun?

A: Saturn

B: Mars

C: Uranus

D: Jupiter

22 What is the seventh planet from the sun?

A: Jupiter

B: Uranus

C: Neptune

D: Pluto

23 What is the sixth planet from the sun?




A: Saturn

B: Mars

C: Jupiter

D: Pluto

ans

1.c 2.a 3.c 4.d 5.a 6.c 7.c 8.c 9.b 10.a 11.c 12.b 13.a 14.b 15.a 16.C 17.b 18.d 19.a 20.b 21.d

22.b 23.a

Wind power generation

1. What does Heating and cooling of the atmosphere generates?

a) Thermo line circulation

b) Radiation currents

c) Convection currents

d) Conduction currents

2. How much is the energy available in the winds over the earth surface is estimated to be?

a) 2.9 X 120 MW

b) 1.6 X 107 MW

c) 1 MW

d) 5MW

3. How much wind power does India hold?

a) 20,000 MW

b) 12,000 MW

c) 140,000 MW




d) 5000 MW

4. What is the main source for the formation of wind?

a) Uneven land

b) Sun

c) Vegetation

d) Seasons

5. Which country created wind mills?

a) Egypt

b) Mongolia

c) Iran

d) Japan

6. “During the day, the air above the land heats up more quickly than the air over water”.

a) True

b) False

7. What happens when the land near the earth’s equator is heated?

a) All the oceans gets heated up

b) Small wind currents are formed

c) Rise in tides

d) Large atmospheric winds are created

8. What type of energy is wind energy?

a) Renewable energy

b) Non-renewable energy

c) Conventional energy




d) Commercial energy

9. What are used to turn wind energy into electrical energy?

a) Turbine

b) Generators

c) Yaw motor

d) Blades

10. What is the diameter of wind turbine blades?

a) 320 feet

b) 220 feet

c) 80 feet

d) 500 feet

11. At what range of speed is the electricity from the wind turbine is generated?

a) 100 – 125 mph

b) 450 – 650 mph

c) 250 – 450 mph

d) 30-35 mph

12. When did the development of wind power in India began?

a) 1965

b) 1954

c) 1990

d) 1985

ans

1.c 2.b 3.a 4.b 5.c 6.a 7.d 8.a 9.a 10.b 11.d 12.c




Chapter 3. Electrical power system

1. The surge impedance of a 110 kV, 3-phase transmission line is 440 ohms. The surge

impedance loading of the line is

b. (110) 2/440 MW

Ans.: (b)

2.The capacitance and inductance per unit length of a 3-phase line, operating at 110 kV are

.01 microfarad and 2.5 mH. The surge impedance of the line is

(a) 50 ohms

(b) 500 ohms

(c) 250 ohms

Ans: (b)

3. A long transmission line is energized at then sending end and is kept open circuited at the

receiving end. The magnitudes of the sending end voltage Vs and of the receiving end

voltage Vr satisfy the following relationship

a. Vs =Vr

b. Vs is greater than Vr

c. Vs is less than Vr

Ans: (c)

4. Voltage regulation of a short transmission line is

a. always positive

b. always negative

c. either positive, negative, or zero




Ans: (c)

5. The capacitance of an overhead line increases with

i. increase in mutual geometric mean distance

ii. Increase in height of conductors above ground

a. Both are true

b. Both are false

c. Only (i) is correct

Ans b

6. Shunt compensation for long EHV lines is primarily resorted to

a. improve voltage profile

b. improve stability

c. reduce fault currents

Ans: (a)

7. Series compensation is primarily resorted to

d. improve voltage profile

e. improve stability

f. reduce fault currents

Ans: (b)

8. Fair weather corona loss may be computed using the empirical formula given by

Peterson. According to Peterson's formula corona loss is proportional to where f and V are

the system frequency and voltage respectively.

(a) f and V2

(b) f 2 and V




Ans: (a)

9. Bundled conductors are used in EHV lines primarily for

a. reducing cost of the line

b. reducing corona loss and radio interference

c. increasing stability limit.

Ans: (b)

10. There are 20 discs in the string of insulators of a 3-phase 400 kV transmission line. String

efficiency is 80 %. The maximum voltage across any disc is

a. 25 kV

Ans: (b)

11. Two or three sheds or petticoats are provided in pin-type insulators in order to increase

a. creepage resistance

b. spark-over voltage(S.O.V)

c. puncture voltage

Ans: (a)

12. Pin -type insulators are use up to

a. 11 kV

b. 33kV

c. 132kV

Ans:(b)




13. Insulators used for transmission line at the dead -end tower are

a. suspension type

b. shackle type

c. strain type

Ans: (c)

14. Economic studies have shown that D.C. transmission is cheaper than a. c transmission

for lengths

a. below 300 km

b. beyond 600 km

c. beyond 1200 km

Ans. b

15.Transmission voltages in the range 230 kV-765 kV are known as

a. High voltage

b Extra High Voltage

c. Ultra High Voltage

Ans. b

16. Which one of the following statements is false?

As the transmission voltage increases,

a. Corona loss decreases

b. Conductor copper loss decreases

c. Cost of insulators, transformers, switches & circuit breakers increases

Ans. C




17. The internal inductance of a solid conductor of radius r and carrying a current I is equal

to

a. 0.5 I * 10-7 H/m

b. 0.5 I * 10-7 exp(-1/4)*r H/m

c. 0.5 * 10-7 H/m

Ans. C

18. Which one of the following statements is not true?

a. The GMD method of finding inductance does not apply to ACSR conductors

b. Current density in ACSR conductors is uniform

c. The GMD between two circular areas, each of different diameters, is equal to the

distance between their centres.

Ans. b

19. Expanded ACSR conductors are used

A To increase the tensile strength of the line

b To reduce corona loss

c. To reduce I2R loss

Ans. b

20. A conductor with 19 strands, each of same diameter and each having an inductance of

L Henries is used for a transmission line. The total inductance of the conductor will be

a.L/19

b. L/361

c. 19L

Ans. A




21. The line to neutral capacitance of single -phase line with conductors of radius 1cm

and spaced 1m apart is equal to

a. 10-9/72 F/m

b. 10-

Ans .a

22. In a double-circuit line with hexagonal spacing ,

a. The phases are balanced, but the conductors of each individual phase are not balanced.

b. The conductors of each individual phase are balanced , but the phases are not balanced

c. The phases, and the conductors of each individual phase are both balanced

Ans. c

23. Which one of the following statements is true?

a. Skin effect at 50 Hz is negligible for larger diameter conductors but becomes appreciable

for smaller conductor.

b. Skin effect at 50 Hz is negligible whatever the diameter of the conductor.

c. Skin effect at 50 Hz is negligible for the smaller diameter conductors but becomes

appreciable for the larger conductor conductor.

Ans. c


a. Resistance of a conductor decreases and the internal inductance increases as the

frequency is increased

B. Resistance and internal inductance of a conductor both increase with increase of

frequency

c. Resistance of a conductor increases and the internal inductance decreases as the

frequency is increased

Ans. c




25. The surge impedance of a double-circuit power transmission line is

a. 40 ohms

b. 200 ohms

c. 400 ohms

d. 800 ohms

Ans. b

26. The surge impedance of a telephone line is

a. 50 ohms

b. 75 ohms

c. 200 ohms

d. 400 ohms

Ans. b

27. Bundle conductors are preferred in EHV transmission lines because

a. It is easy to fabricate thin conductors and combine them to make a bundle

b. Inductance of the line is reduced, and the corona loss, and radio & TV interference is

minimized.

c. Tower height is reduced and hence transmission cost is low.

Ans. b

28. Inductive interference between power & communication lines can be minimized by

a. Increasing the spacing of power line conductors

b. Transposing power line conductors

c. Transposing communication line conductors

d. Either b or c.




Ans. d

29. The percentage regulation of an overhead transmission line can be zero when the

load power factor is

a. Lagging

b. Unity

c. Leading

Ans. C


a. Skin effect increases the resistance of a conductor ,but proximity effect decreases

the resistance

b. Both skin effect and proximity effect increase the resistance of a conductor

c. Both skin effect and proximity effect increase the internal inductance of a conductor

Ans. b

31. A transmission line having parameters A1, B1, C1, D1 is in parallel with another having

parameters A2, B2, C2, D2. The overall " A " parameter of the combination is

a. A1A2 +B1C2

b. (A1B2 +A2B1)/(B1+B2)

c. C1+C2 + (A1-A2)(D2-D1)/(B1+B2)

Ans. B




Chapter4. Power factor improvement of load

Q1. Power factor can be improved by connecting which among these?

a. Static capacitors.

b. Resistors.

c. Synchronous condensers.

d. Both (a) and (c).

ANSWER: d. Both (a) and (c).

Q2. What is the advantage of the static capacitors?

a. Low losses.

b. Easy installation.

c. Lower maintenance.

d. All of the above.

ANSWER: d. All of the above.

Q3. Which among these is the advantage of synchronous condensers?

a. Helps in achieving the stepless control of power factor.

b. The motor windings have a lower thermal stability.

c. The maintenance cost is low.

d. All of the above.

ANSWER: a. Helps in achieving the stepless control of power factor.

Q4. Phase advancers are used for which among the following machines?

a. Transformers

b. Synchronous machines.

c. Induction motors.




d. DC machines.

ANSWER: c. Induction motors.

Q5. What is the main disadvantage of phase advancers?

a. Cannot be used for motors below 200 H.P

b. Produces noise.

c. Can be used where synchronous motor is un admissible.

d. None of these.

ANSWER: a. Cannot be used for motors below 200 H.P

Q6. The most suitable location for the power factor improvement device is

a. Near the electrical appliance which is responsible for the poor power factor.

b. At the sending end.

c. At the receiving end in case of transmission lines.

d. Both (a) and (c).

ANSWER: d. Both (a) and (c).

7. The capacitor preferred for high circuits is

(a) air capacitor

(b) mica capacitor

(c) electrolytic capacitor

(d) none of the above

Ans: b

8. The capacity of capacitor bank used in power factor correction is expressed in terms of

(a) kW

(b) kVA




(c) kVAR

(d) volts

9. In a transformer the voltage regulation will be zero when it operates at

(a) Unity p.f.

(b) Leading p.f.

(c) Lagging p.f.

(d) Zero p.f. leading

ANS B

10. A motor which can conveniently be operated at lagging as well as leading power factors

is the

(a) Squirrel cage induction motor.

(b) Wound rotor induction motor.

(c) Synchronous motor.

(d) DC shunt motor.

ANS: D

11.In a transformer, zero voltage regulation at full load is

(a) Not possible

(b) Possible at unity Power factor load

(c) Possible at leading Power factor load

(d) Possible at lagging Power factor load

ANS C




12. A power factor meter has

A.One current circuit and two pressure circuits

B.One current circuit and one pressure circuit

C.Two current circuits and one pressure circuit

D.None of the above

ANS A

13.The two pressure coils of a single phase power factor meter have

A.The same dimensions and the same number of turns

B.The same dimensions and the but different number of turns

C.The same number of dimension of turns but different dimension

D.None of the above

ANS A

14.In a single phase power factor meter the phase difference between the currents in the

two pressure coils is

A.Exactly 00

B.Approxminately 00

C.Exactly 900

D.Approxminately 900

ANS C




Chapter5. Mechanical features and design of overhead

transmission line

1. Which of the following material is not used for overhead line insulators?

a) Porcelai

b) Glass

c) PVC

d) Steatite

2. Pin type insulator are mostly subjected to which type of mechanical stress?

a) Compressive stress

b) Tensile stress

c) Both tensile and compressive stress

d) Twisting stress

3. Which of the following is the main field of application of pin type insulator?

a) Distribution system

b) Transmission system

c) Transmission and distribution system

d) EHV transmission system

4. Suspension type insulator are subjected to ______________

a) tensile stress

b) compressive stress

c) tensile and compressive stress

d) depends on its use




5. A transmission line consists of 9 discs of suspension insulator in each string. What is the

operating voltage of the transmission line?

a) 11 KV

b) 33 KV

c) 66 KV

d) 132 KV

6. Suspension insulator are made up of _____________

a) glass

b) porcelain

c) steatite

d) epoxy resin

7. Which of the following insulator is similar to pin type insulator?

a) Suspension insulator

b) Post insulator

c) Strain insulator

d) Shackle insulator

8. Which type of insulator is used where there is dead end of the line or there is a corner or

a sharp curve, for high voltage line?

a) Pin type insulator

b) Shackle insulator

c) Strain insulator

d) Stay insulator




9. What is the most common cause of failure of overhead line insulators?

a) Flashover

b) Mechanical stress

c) Porosity of materials

d) Improper vitrification

10. If a string of suspension insulator has three units, each can withstand a maximum 11 KV

and total string can withstand 25.76 KV. What is the string efficiency?

a) 234.1%

b) 46.3%

c) 68.75%

d) 78%

11. Voltage distribution across disc of strings of suspension insulator assembly is ______

a) same for all disks

b) maximum for unit nearest to the line

c) maximum for unit nearest to the tower

d) equal to transmission line voltage rating

ANS

1c. 2.d 3.a 4.a 5.d 6.b 7.b 8.c 9.a 10.d 11.b

12. What should be the minimum insulation resistance of a 11 kV line when tested with a

1000 v Megger?

a. 10 kV

b. 50 kV

c. 33 kV

d. 120 kV




13. Which test(s) is / are conducted after completion of erection of 11 kV line but before

energisation of lines?

a. Conductor continuity tests

b. Earth resistance tests

c. Insulation resistance tests

d. Both (a) & (c)

e. All of these

14.What is the empirical formula employed for the determination of spacing of conductors

in case of aluminium conductors?

a. √S + V / 100

b. √S + 120 / V

c. √S + V / 150

d. √S + V / 1 kV

15.What is the angle between the pole and stay?

a. 30 °

b. 45 °

c. 60 °

d. 10 °

16. What should be the spacing between the two conductors if the working voltage is 11

kV?

a. 76 mm

b. 101 mm

c. 190 mm

d. 250 mm




ANS

12.B 13.E 14.C 15.A 16.B




Chapter 6 Transmission line parameter

1.Fill in the blanks by inserting appropriate words/figures.

(i)The power loss in an overhead transmission line is mainly due to ....................... .

(ii)If the length of a transmission line increases, its inductance is ....................... .

(iii)The d.c. resistance of a line conductor is than its a.c. resistance.

(iv)If capacitance between two conductors of a 3-phase line is 4 microF, then capacitance of

each conductor to neutral is ................... .

(v)If the length of the line is decreased, its capacitance is ..................... .

(vi)Transposition of a 3-phase transmission line helps in ................ .

(vii)A neutral plane is one where is zero.

(viii)In a single phase overhead line, the neutral plane lies at ..................... .

2.Pick up the correct words/figures from brackets and fill in the blanks

(i)If the supply frequency increases, then skin effect is ....................

A. [increases,

B. decreased]

(ii)An overhead transmission line has appreciable inductance because the loop it forms has

..............

X-sectional area.

A. [large,

B. small]

(iii)If the spacing between the conductors is increased, the inductance of the line...........

A. [increases,

B. decreases]




(iv)The skin effect is for stranded conductor than the solid conductor.

A. [less,

B. more]

(v)If the conductor diameter decreases, inductance of the line is ..........

A. [increased,

B. decreased]

ans

1.(i) Line conductor resistance (ii) increased (

inductance and capacitance of the three phases (vii) electric intensity (viii) the centre of the

distance between the conductors

2.(i) increased (ii) large (iii) increases (iv) less (v) increased




Chapter 7 Underground cable

1. Fill in the blanks by inserting appropriate words/figures. (i)The underground system is..........costly than the equivalent overhead line system. (ii)Voltage drop in cable system is less than that of equivalent overhead line because of...........of conductors in a cable. (iii)A metallic sheath is provided over the insulation to protect the cable from.................... . (iv)In single-core cables, armoring is not done in order to avoid................... (v)The most commonly used insulation in high-voltage cables is............ (vi)Belted cables are generally used up to..............kV. (vii)The working voltage level of belted cable is limited to 22 kV because of the............set up in the dielectric. (viii)For voltages beyond 66 kV, solid type cables are unreliable because there is a danger of breakdown of insulation due to the....................... (ix)If the length of a cable increases, its insulation resistance................. (x)Under operating conditions, the maximum stress in a cable is at.................

2.Fill in the blanks by picking up correct words/figures from brackets. (i)For voltages less than 66 kV, a 3-phase cable usually consists of...............

A. 3-core cable B. 3 single-core cables

(ii)If the length of a cable is doubled, its capacitance is

A. doubled B. halved C. quadrupled

(iii) A certain cable has an insulation of relative permittivity 2. If the insulation is replaced by one of relative permittivity 4, then capacitance of cable is .................. doubled halved (iv)The minimum dielectric stress in a cable is at..................

A. conductor surface B. lead sheath




(v)If a cable of homogeneous insulation has maximum stress of 5 kV/mm, then the dielectric strength of insulation should be..................

A. 5-kV/mm B. 2•5 kV/mm C. 3 kV/mm

(vi)In capacitance grading of cables, we use a ............... dielectric.

A. homogeneous B. composite

(vii)For the same safe potential, the size of a graded cable will be.........

A. less B. more

(viii)For operating voltages beyond 66 kV ………….... cables are used. Belted

A. S.L. type B. oil-filled

(ix)Voids in the layers of impregnated paper insulation..............the breakdown voltage of the cable.

A. increase B. decrease

(x)For voltages beyond 66 kV, 3-phase system usually employs..................

A. 3-core cable B. 3 single core cables

1. (i) more (ii) closer spacing (iii) moisture (iv) excessive sheath losses (v) impregnated paper (vi) 11 (vii) tangential stresses (viii) presence of voids (ix) decreases (x) conductor surface 2.(i) 3-core cable (ii) doubled (iii) doubled (iv) lead sheath (v) 5 kV/mm (vi) composite

(vii) less (viii) oil-filled (ix) decrease (x) 3 single-core cables




Chapter 9. Neutral grounding

1.Fill in the blanks by inserting appropriate words/figures : (i)When single line to earth fault occurs on an ungrounded neutral system, the voltages of the healthy phases (other than the faulty phase) rise from their normal phase voltages to ............... . (ii)When single line to earth fault occurs on an ungrounded neutral system, the capacitive current in the two healthy phases rises to............times the normal value. (iii)When single line to earth fault occurs on an ungrounded neutral system, the capacitive fault current becomes.............times the normal per phase capacitive current. (iv)In Peterson coil grounding, inductance L of the coil is related to line to earth capacitance C as.................... (v)When single line to earth fault occurs in solid grounding system, the phase to earth voltage of the remaining two healthy phases remain at ................... .

2.Pick up the correct words/figures from brackets and fill in the blanks. (i)The ungrounded neutral system cannot provide adequate protection against earth faults because the capacitive fault current is ...................

A. Small B. very large

(ii)In Peterson coil grounding, when inductive fault current becomes equal to capacitive current of the system, then ...................

A. (XC = 3XL B. XL = 3XC)

(iii)In voltage transformer grounding of single phase transformer is connected between neutral and earth.

A. (Secondary, B. primary)

(iv)In equipment grounding, the enclosure is connected to ................... wire.

A. (ground B. neutral) C.




(v)he ground wire is coloured ................... .

A. (black B. green)

(vi)The neutral wire is coloured ................... .

A. (black B. green)

(vii)In Peterson coil grounding, the inductance of the coil is ................... .

A. (fixed B. variable)

(viii)In case of earth fault, the ungrounded neutral system....................lead to arcing ground.

A. (does B. does not)

(ix)Grounding transformer is used where neutral ................... available.

A. (is B. is not)

(x)Most of the faults on an overhead system are...............................faults.

A. (phase to earth B. phase to phase)

Ans 1.(i) line (v) normal phase voltage 2.(i) small (ii) XC = 3XL (iii) primary (iv) ground (v) green (vi) black (vii) variable (viii) does (ix) is not (x) phase to earth




Chapter 8. Substation 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 2. 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 3. 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 4. In substation which of the device is a carrier communication device: a) CVT b) Earth conductor c) Wave trap d) Lightning arrestor C 5. 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




6. 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 7. 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 8. Emulsifier protection is associated with: a) Grounding protection b) Dielectric strength protection of cables and conductors c) Lightning protection d) Fire protection D 9. 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 10. 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 11.The preferred Air Force base distribution system is




A. 34.5 kV B. 69 kV C. 3-phase,4wire D. Single-phase, 3-wire

ans C 12. Which of these equipment items is designed to open a circuit automatically under load and then restore the service quickly once the fault has cleared?

A. Fused cutout B. Sectionalizer C. Pole-top switch D. Recloser

D 13.Which of the following items supply control voltage to operate circuit breakers?

A. Batteries B. Signal generators C. Current transformers D. Distribution transformers

A 14. What are the minimum requirements for a substation fence?

A. Two strands of barbed wire above a 6-foot-high fence B. Two strands of barbed wire above a 7-foot-high fence C. Three strands of barbed wire above a 6-foot-high fence D. Three strands of barbed wire above a 7-foot-high fence

D 15. How many feet past the substation fence must the perimeter ground wire extend?

A. 2 B. 5 C. 8 D. 10

A 16. Which is not a major function of an oil circuit breaker?

A. To provide a means of switching under load B. To stabilize current flow during an overload situation C. To protect the system by automatically opening the circuit when a fault occurs D. To minimize damage to a system by openning the circuit when a overload occurs

B 17. What OCB component supplies amperage to the protective relays?

A. Timer ports B. Main contacts




C. Terminal bushings D. Current transformers

D 18. What percent of eletrical system faults are temporary?

A. 25% B. 55% C. 75% D. 95%

D

faculty of degree engineering - 083 - dr. subhash technical

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