HVE MCQ

1. Multiple Choice Questions
Unit
no
(a) (b) (c ) (d) Answer
1 For electric stress control,followingequation
▼2 .φ = - ρ/ ε0 of
Poisson's
equation
Laplace's
equation
Guass
theorem
Charge density (b)
2 Which theory explains the mechanismfor
breakdown under different conditions?
Townsend
theory
Streamer
theory
Clump
theory
Only (a) and (b) (d)
2 Corona results in improvement
in power
factor
increased
capacitive
reactanceof
transmission
lines
radio
interference
better
regulation
(c )
2 Inelastic collisionsarethosein which internal
changes in energy take placewithin an atom or a
molecule at the expenses of total kinetic energy
of the collidingparticle.Suitableexamplefor
inelastic collisionsis/are
Ionization Attachment Excitation All of these (d)
2 The Townsend mechanismexplains the
phenomenon of breakdown Only at low
pressure
Only at high
pressure
Only at very
high
pressure
Only bat very
low pressure
(a)
3 For applicationsin power cables,the dielectrics
most commonly used is
Mineral oil Polyolefins Benzene Diphenyl (b)
2 Intrinsicbreakdown occurs in time of the order
of
10-5 s 105 s 10-8 s 108 s (c )
2 Within dielectric,an electron startingfrom the
cathode will drifttowards the anode and during
this motion
Gains energy
from the
field and
loses during
collision
Gains energy
duringboth
motion and
collision
Loses energy
duringboth
motion and
collision
Loses energy
from the field
and gains
duringcollision
(a)
2 By comparingTownsend’s theory and Paschen’s
criteria followingcharacteristic isobtained.
pdmin = 0.84
and Vmin =
311
pdmin = 0.79
and Vmin = 320
pdmin = 0.89
and Vmin =
325
pdmin = 0.74
and Vmin = 320
(c )
In characteristicassumeA = 12, B = 365 and ɤ =
0.02 for air.What is the valueof pdmin and Vmin ?
2 In an experiment in a certain gas itwas found
that the steady state
current is 5.5 x 10-8 A at 8 kV at a distanceof 0.4
cm between the plane electrodes.
Keeping the field constantand reducing the
distanceto 0.1 cm results in a current of 5.5 x
6.776
collisions/ cm
7.676
collisions/ cm
6.767
collisions/ m
7.467
collisions/ m
(b)

2. 10-9 A. Whatis the Townsend's primary
ionization coefficientα.
2 The corona inception and breakdown voltages of
the sphere-planearrangement are shown in Fig.
Find out the correct statement.
at small
spacing
(region I),the
field is
uniform, and
the
breakdown
voltage
mainly
depends on
spacing.
at fairly large
spacings
(region II),the
field is non-
uniform, and
the
breakdown
voltage
depends both
on the sphere
diameter and
the spacing
at large
spacings
(region III),
the field is
non-uniform,
and the
breakdown
is
preceded by
corona and is
controlled
only by the
spacing.The
corona
inception
voltage
mainly
depends on
the sphere
diameter
(a) , (b) & (c
) are
correct
(d)
2 The statistical timelegdepends on Amount of
the
preionization
present in
between the
gap
Size of the
gap
Amount of
over voltages
applied to
the gap
All of these (d)
2 For Sulpher Hexa Floridewhich statement is
incorrect?
It is stored in
a steel
cylinder
It can be used
much above
14 KG/CM2 to
avoid
liquidification
Dielectric
strength is 2
to 3 times
than Air
Capability to
absorb more
number of
electrons
(b)
1 Dielectric material has a highly curved surface,
two dimensional field and non-uniformfield, for
electric stress analysis which method gives
accurateresult?
Charge
Simulation
Method
Finite
Difference
Method
Finite
Element
Method
All of these (c )
3 In Solid dielectric breakdown ,the spreadingof
spark channels duringtracking,in theform of
the branches is called
Bunching Treeing sparking Treeing &
sparking
(b)
3 The temperature limitfor class ‘F’insulation is 155°C 120°C 130°C 165°C (a)
1 The voltage which produces the loss of dielectric
strength of insulation is known as
Withstand
voltage
Disruptive
discharge
voltage
Flashover
voltage
Impulsevoltage (b)
2 Formative time lagdepends on the mechanism
of the avalanchegrowth in gap. The formative
time lagis usually
Much shorter
than the
statistical
time lag
Much greater
than the
statistical
time lag
Equal to the
statistical
time lag
None of these (a)
2 For the high voltage conductors at high
pressures,if the voltage is positivethen the
corona appears as a
Reddish
glowing
spots
Uniform
greenish
spots
Uniform
bluish white
sheath
None of these (c )
3 The increasein liquid hydrostatic pressure Increases the
breakdown
strength
Decreases the
breakdown
Does not
affect the
breakdown
None of these (a)

3. strength strength
3 In caseof solid particles presentin the liquid and
in caseof presence of only gas bubbles in liquids,
the direction of force is towards
Areas of
minimum
stress,areas
of maximum
stress
Areas of
minimum
stress,areas
of minimum
stress
Areas of
maximum
stress,areas
of minimum
stress
Areas of
maximum
stress,areas of
maximum
stress
(c )
3 Accordingto the Stressed Oil Volume theory,
the breakdown strength is
Directly
proportional
to the
stressed oil
volume
Directly
proportional
to the square
of the
stressed oil
volume
Inversely
proportional
to the
stressed oil
volume
Inversely
proportional to
the squareroot
of stressed oil
volume
(c )
3
Accordingto the Bubble theory, once a bubble
is formed, itwill elongate in the direction of
electric field under the influenceof electrostatic
forces. Duringelongation the volume of bubbles
Remains
constant
Increases
Decreases
None of these
(a)
2 The essential condition for the Paschen's lawto
be valid is that
humidity
must be low.
temperature
must be
constant
voltage must
be DC
voltage must
be AC
(b)
3 Electro-mechanical breakdown of solid insulating
materials occurs dueto
electrical
stresses
produced by
the voltage
fluctuations.
mechanical
stresses
produced by
the electrical
field
magnetic
bum
vibrations (b)
3 Long term deterioration and breakdown occurs
in solid dielectric
Thermal
phenomenon
Surface
discharges
Internal
discharges
Treeing
phenomenon
(c )
3 The parameters that affect the breakdown
strength of liquid is
Pressure,
temperature,
suspended
particals,
dissolved
impurities
Hydrostatic
Pressure,
temperature,
dielectric
constant
Pressure,
temperature,
suspended
particals
Hydrostatic
Pressure,
temperature,
dielectric
constant,
dissolved
impurities
(a)
3 In which type of breakdown, an avalanche of
electrons is formed? Defect
Breakdown
Intrinsic
Breakdown
Thermal
Breakdown
Electrochemical
Breakdown
(b)
4 A Tesla coil is a cascaded
transformer
coreless
transformer
high
frequency
resonant
transformer
low impedance
transformer
(c )
4 Van de Graaff generators areuseful for Very high
voltage and
low current
applications
Very high
voltage and
high current
applications
Constant
high voltage
and current
applications
High voltage
pulses only
(a)

4. 4 The voltage doubler circuitis suitablefor the
voltage up to
2V 4V 6V 8V (b)
4 In Van de Graaff generators, the shape of high
voltage electrode is nearly spherical.Which of
the followingstatement is incorrect?
Minimize
high surface
field
gradients
Avoid Corona Increasethe
length of
electrode
MinimizeLocal
discharges
( C)
4 A generating voltmeter is a Constant
capacitor
electrostatic
voltage
generator
Variable
capacitor
electrostatic
voltage
generator
Variable
inductor
electrostatic
voltage
generator
Constant
inductor
electrostatic
voltage
generator
(b)
4 Series capacitancevoltmeters were used with
cascadetransformers for measuringrms values
up to
100 kV 500 kV 800 kV 1000 kV (d)
4 The disadvantages of resonanttransformers is Additional
variable
chokes
Pure sine
wave output
No high
power arcing
No repeated
flashovers
(a)
4 In a multistageimpulsegenerator, for producing
very high voltages,a bank of capacitors is
Charged in
parallel and
then
discharged in
series
Charged in
series and
then
discharged in
parallel
Charged in
parallel and
then
discharged in
parallel only
Charged in
series and then
discharged in
series only
(a)
4 In largeimpulsegenerators, the spark gaps are
generally
Sphere gaps Hemispherical
gaps
Square gaps Either (a) or (b) (d)