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HIGH VOLTAGE

Total questions: 81

Worksheet time: 1hrs 21mins

Name
Class
Date
1.

Enter enrollment Number

4 lines
2.

An experiment method for computing the field distribution is

a)

solution of laplace equation

b)

electrolytic tank method

c)

digital solution

d)

field intensity method

3.

Finite element method used only with

a)

field which are bounded

b)

filed which are unbounded

c)

both bounded and unbounded

d)

high accuracy is not required

4.

Most suitable method to solve electrostatic field problem is

a)

Laplace equation

b)

charge simulation method

c)

finite difference method

d)

resistance analog method

5.

The accuracy obtain in numerical computation of electric field is usually

a)

very high

b)

at very low

c)

5 to 10 %

d)

2 to 5%

6.

Electrical conduction in gases was first studied in 1905 by

a)

Loeb

b)

Maxwell

c)

Townsend

d)

Hertz

7.

An electronegative gas is one in which

a)

positive ions formed along with electrons

b)

gas has inherent negative charge

c)

gas is ionized due to electron bombardment

d)

gas in which electron get attached to from negative ion.

8.

SF6 is a

a)

neutral gas

b)

electronegative gas

c)

ionizes easily to form ions

d)

non attaching gas

9.

Ionization coefficients  α\alpha   γ\gamma  are function of

a)

applied voltage

b)

pressure and temperture

c)

electrical field 

d)

ration of electrical field to pressure

10.

Time lag is dependent upon

a)

time difference between instant of applied voltage and occurrence of breakdown

b)

time difference between instant of applied voltage and occurrence of electrical field

c)

time difference between instant of applied voltage and pressure

d)

all above

11.

streamer mechanism of breakdown explain phenomena of electrical breakdown of

a)

very short spark gaps

b)

very long spark gaps

c)

spark subjected to impulse volatges

d)

very long gaps where filed is non-uniform

12.

Minimum sparking potential of air is about

a)

100V

b)

100KV

c)

325V

d)

325KV

13.

for a 1 cm gap in air at 760 mm pressure and 20C temperture the breakdwon voltge is

a)

24KV

b)

24.5 KV

c)

30.3 KV

d)

30.4 KV

14.

The requirement of gases for insulation purpose is

a)

high dielectric strength the thermal stability

b)

high dielectric strength only

c)

high thermal stability

d)

low thermal stability

15.

The mechanism of a gases for insulation purpose is

a)

partical exchange

b)

clump formation

c)

filed emission

d)

all of above

16.

SF6 has the following property which is not favorable for use in electrical apparatus:

a)

High dielectric strength

b)

low dielectric strength

c)

It is not environmental friendly and causes global warming

d)

None of the above

17.

The breakdown voltage of spark gap for impulse voltage is .................compare to the breakdown voltage of power frequency ac

a)

same

b)

larger

c)

smaller

d)

none of above

18.

Among gases used electrical insulation which gas the highest breakdown strength at atmospheric pressure?

a)

Air

b)

Nitrogen

c)

SF6

d)

Oxygen

19.

Transformer oil is

a)

askeral

b)

silicone oil

c)

polyester

d)

mineral oil

20.

The breakdown strength of mineral oil is about

a)

20 KV/mm

b)

50 KV/mm

c)

3 to 5 KV/mm

d)

120 KV/mm

21.

 tan⁡δ\tan\delta  for liquid insulants at 50 Hz should less than

a)

0.1

b)

0.001

c)

0.0005

d)

 10−610^{-6}  

22.

Dielectric constant of mineral oils is about

a)

1.5 to 2

b)

2.2 to 2.9

c)

1.008

d)

2.2 to 2.4

23.

conduction and breakdown in commercial liquid is affected by

a)

solid partical

b)

vapour or air bubbles

c)

electrode material

d)

all above

24.

stressed oil volume theory is applicable when

a)

small volume of liquid is involved

b)

large volume of liquid is involved

c)

large gap distance is involved

d)

pure liquids are involved

25.

The parameter that effect the breakdown strength of liquid is

a)

pressure temperature dissolved impurities and suspended particles.

b)

dielectric constant

c)

dissolved imputites

d)

hydrostatic pressure

26.

In pure liquid dielectric with increase in hydrostatic pressure the breakdown stress

a)

increase linearly up to some extent and does not change afterward

b)

increases exponentially

c)

decreases

d)

none of above

27.

The intrinsic breakdown stregth of solid dielctric is

a)

50 to 100 kv/mm

b)

500 to 1000 kv/mm

c)

5 to 10 kv/mm

d)

1 to 5 kv/mm

28.

The usual mechanism breakdown in solid dielectric is

a)

intrinsic breakdown

b)

electro mechanical breakdown

c)

thermal breakdown

d)

chemical breakdown

29.

Long term deterioration and breakdown occurs in solid dielectric due to

a)

thermal phenomenon

b)

surface discharge

c)

internal discharge

d)

treeing phenomenon

30.

paper insulation is used in

a)

cable and capacitor

b)

transformer

c)

rotating machine

d)

circuit breaker

31.

Thermal classification of insulating material is done

a)

gases

b)

liquid

c)

solid

d)

composite insulation

32.

Breakdown due to internal discharge develop

a)

in millisecond

b)

in few second

c)

over a long duration of several days

d)

all above

33.

Aging in electrical insulating material under electrical field means

a)

gradual reduction in dielectric strength which may lead to breakdown

b)

decrease in insulation resistance of materials

c)

progressive building up of distributive discharge inside material

d)

all the above

34.

For generator coil insulation the class of insulation used in

a)

class A

b)

class B

c)

class C

d)

class F

35.

The insulation used in high voltage circuit breaker of large power rating is

a)

air

b)

vacuum

c)

SF6

d)

mineral oil

36.

For HV cable insulation the material used are

a)

glass and ceramic

b)

silicone rubber

c)

XLPE

d)

paper-oil insulation

37.

Gas insulation is now a days used in which application

a)

Generator

b)

Motor

c)

Transformer

d)

Circuit Breaker and substation

38.

Resins and varnishes are mainly used for

a)

Transformer coil impregnation

b)

Generator and motor coil impregnation

c)

In cable and capacitor insulation

d)

overhead line insulation

39.

In high voltage switchgear, the insulation used inside breaker is

a)

Epoxy resin

b)

Procelain

c)

Vulcanized

d)

Fiber and resin bonded glass fiber

40.

Synethetic liquid dielectric are mainly used

a)

capacitor and cable insulation as impregnates

b)

In transformer insulation

c)

In circuit breaker

d)

all above

41.

Peak to peak ripple is define as

a)

the difference between average dc voltage and peak value

b)

the difference between maximum and minimum and maximum dc voltage

c)

only dc rms value

d)

None above

42.

In testing with a reasonat transformer the output voltage is

a)

rectangular wave

b)

triangular wave

c)

trapezoidal wave

d)

pure sine wave

43.

Parallel resonant transformer the output voltage is

a)

large test voltage are needed

b)

stable output voltage with high rate of rise voltage is needed

c)

large current is needed

d)

small current is needed

44.

Tesla coil used for

a)

generation of sinusoidal output voltage

b)

generation of very high voltage

c)

generation of rectangular voltage

d)

generation of high frequency ac voltage

45.

Average electrical field is magnitude of electrical field

a)

at mid point between conductors

b)

ratio of potential difference to the distance between conductors

c)

at surface of the lower potential electrode

d)

at surface of the higher potential electrode

46.

The value of charging voltage used in medium size impulse generator is

a)

10 to 50 KV

b)

50 to 100 KV

c)

500 Kv

d)

any value

47.

In an impulse current generator the capacitor connected

a)

series

b)

parallel

c)

connected in parallel while charging and series while discharge

d)

connected in series while charging and parallel while discharge

48.

A trigetron gap is used with

a)

cascade transformer unit

b)

impulse current unit

c)

impulse voltage unit

d)

dc voltage double units

49.

The energy rating of different resistor in impulse generator of medium and large size

a)

less than 1 KJ

b)

10 to 20 KJ

c)

1 to 2 KJ

d)

2 to 5 KJ

50.

voltage stabilizer used for regulating high dc voltage are

a)

series type

b)

shunt type

c)

both series and shunt type

d)

shunt or series or degenerating

51.

A series capacitor voltmeter measure

a)

dc voltge

b)

ac voltage

c)

ac voltage peak value

d)

impulse voltage

52.

Electrostatic voltmeter can measure

a)

only dc voltge

b)

both dc and ac voltage up to high frequency

c)

impulse volatge

d)

none above

53.

A generating voltmeter is used

a)

impulse voltage

b)

ac voltage

c)

dc voltage

d)

high frequency ac voltage

54.

CVT when tuned does not have

a)

ratio error

b)

phase angle error

c)

both ration and phase angle errors

d)

temperature error

55.

sphere gaps are used to measure

a)

dc voltage

b)

ac peak voltage

c)

dc ac peak and impulse voltages

d)

on dc peak voltage

56.

The main factor that effect the spark over voltage of sphere gap are

a)

humidity and waveform

b)

nearby earthed objects and atmospheric condition

c)

diameters of the sphere

d)

gap spacing diameter and waveform

57.

Rogoswski coil and high frequency current transformer have bandwidth of about

a)

100 Khz

b)

10 Mhz

c)

1.0 Mhz

d)

1100 Mhz

58.

with series capacitor voltmeter large error will result when

a)

capacitance is larger

b)

meter used is an electromechanical meter

c)

voltage to be measured non-sinusoidal and contain harmonics

d)

none above

59.

To measure high volatge of peak value for 150 kv suitable sphere gap would be

a)

5 or 10

b)

10 or 15

c)

15 or 25

d)

50 or 100

60.

which instrument measure impulse current of short duration

a)

park tubular shunt

b)

current transformer

c)

hall generator

d)

Faraday ammeter

61.

The electric field developed with in cloud before lighting stroke occurs can be of the order of

a)

0.1 KV/cm

b)

1.0 KV/cm

c)

100 KV/cm

d)

10 KV/cm

62.

The velocity of return or main stroke may be

a)

0.01 C

b)

0.001C

c)

0.1 C

d)

0.8 C

63.

The peak value of lighting stroke currents are of order

a)

100 A

b)

1000 A

c)

10 to 100 kA

d)

0.1 KA

64.

The cumulative probability of 10 kA lighting stroke current is about

a)

0.6

b)

0.2

c)

0.1

d)

0.98

65.

switching overvoltage in power system network in order of

a)

1.5 pu

b)

2.5 to 3.5 pu

c)

10 pu or more

d)

1 pu

66.

The material used in gaps less surge arresters used in hv power system is

a)

graphite

b)

aluminium oxide

c)

zinc oxide

d)

metal oxide

67.

The duration of switching surges in GIS is

a)

milisecond

b)

microsecends

c)

few nanosecond and less than a microsecond

d)

none above

68.

For resistivity and dielectric constant measurement the electrode system used

a)

two electrode

b)

three electrode

c)

four electrode

d)

none of above

69.

The power supply used in resistivity measurement is

a)

110 V

b)

250 V

c)

500 V

d)

500 to 2000 V

70.

Loss of charge method is used to deteime

a)

insulation resistance

b)

dielectric constant

c)

loss factor

d)

rate of charging of capacitor

71.

The equivalent circuit of loosy capacitor is

a)

R-C series circuit

b)

R-R series circuit

c)

R-C parallel circuit

d)

R-L series circuit

72.

Partial discharge magnitude is

a)

quantity of charge measured at the terminals of the specimen

b)

crake in solid material

c)

voltage across solid materials

d)

none above

73.

Fifty percentage flash over voltage is define as

a)

the voltage at which the flash over probability is 0.5

b)

the voltage at which the flash over probability is 0.15

c)

the voltage at which the flash over probability is 0.20

d)

the voltage at which the flash over probability is 0.50

74.

Most important test on isolatros are

a)

voltage withstand test

b)

short circuit test

c)

high current test

d)

temperature rise test

75.

Fault location in an HV cable is done by

a)

voltage withstand test

b)

partial discharge scanning test

c)

life test

d)

impulse test

76.

In impulse test of transformer fault location is usually done

a)

neutral current oscillogram

b)

chopped wave oscillation

c)

observing for noise or smoke

d)

scanning method

77.

Most important test on assert the proper functions of surge divertor is

a)

100 % impulse test

b)

front of wave spark over and residual voltage test

c)

impulse current test

d)

pollution test

78.

The salt-fog test done on insulatros

a)

impulse test

b)

power frequency pollution test

c)

impulse current test

d)

impulse voltage test

79.

C - tan⁡ δ\tan\ \delta  test on bushing is done using

a)

impulse generator

b)

high voltage schering bridg

c)

low voltage schering bridge

d)

resoant transformer

80.

Impulse test of transformer indicates

a)

dielectric strength quantity of insulation and processing

b)

Full wave standard impulse

c)

Chopped wave standard impulse

d)

Half wave standard impulse

81.

The tests which are not performed under power frequency tests is

a)

Partial discharge tests

b)

Momentary withstand test

c)

Visible discharge tests

d)

Full wave withstand tests

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