List Of Switchgear Protection Objective Questions
1.Fault diverters are basically
fuses
relays
fast switches
circuit breakers
ANSWER : : fast switches
2.Relays can be designed to respond to changes in
resistance, reactance or impedance
voltage and current
light intensity & temperature
all above
ANSWER : : all above
3.On which of the following routine tests are conducted ?
Oil circuit breakers
Air blast circuit breakers
Minimum oil circuit breakers
All of the above
ANSWER : : All of the above
4.Circuit breakers are essentially
current carrying contacts called electrodes
arc extinguishers
circuits to break the system
transformers to isolate the two systems
ANSWER : : current carrying contacts called electrodes
5.Magnetic circuit breaker has ______ trip action.
delayed
instantaneous
both of the above
none of the above
ANSWER : : instantaneous
6.A differential relay measures the vector difference between
two currents
two voltages
two or more similar electrical quan�tities
none of the above
ANSWER : : two or more similar electrical quan�tities
7.A thermal protection switch can protect against
short-circuit
temperature
overload
over voltage
ANSWER : : overload
8.Thermal overload relays are used to protect the motor against over current due to
short-circuits
heavy loads
grounds
all of the above
ANSWER : : heavy loads
9.The arcing contacts in a circuit breaker are made of
copper tungsten alloy
porcelain
electrolytic copper
aluminium alloy
ANSWER : : copper tungsten alloy
10.An efficient and a well designed protective relaying should have
good selectivity and reliability
economy and simplicity
high speed and selectivity
all of the above
ANSWER : : all of the above
11.SF6 gas
is yellow in colour
is lighter than air
is nontoxic
has pungent small
ANSWER : : is nontoxic
12.Circuit breakers usually operate under
transient state of short-circuit current
sub-transient state of short-circuit current
steady state of short-circuit current
after D.C. component has ceased
ANSWER : : transient state of short-circuit current
13.D.C. shunt relays are made of
few turns of thin wire
few turns of thick wire
many turns of thin wire
many turns of thick wire
ANSWER : : many turns of thin wire
14.Burden of a protective relay is the power
required to operate the circuit breaker
absorbed by the circuit of relay
developed by the relay circuit
none of the above
ANSWER : : absorbed by the circuit of relay
15.In order that current should flow without causing excessive heating or voltage drop, the relay contacts should
have low contact resistance
be clean and smooth
be of sufficient size and proper shape
have all above properties
16.Thermal circuit breaker has
delayed trip action
instantaneous trip action
both of the above
none of the above
ANSWER : : delayed trip action
17.Which of the following medium is employed for extinction of arc in air circuit breaker ?
Water
Oil
Air
SF6
ANSWER : : Air
18.Air blast circuit breaker is used for
over currents
short duty
intermittant duty
repeated duty
ANSWER : : repeated duty
19.The current zero interruption, in oil and air blast circuit breakers, is achieved by
lengthening of the gap
cooling and blast effect
both (a) and (b)
deionizing the oil with forced air
ANSWER : : both (a) and (b)
20.The relay operating speed depends upon
the spring tension
the rate of flux built up
armature core air gap
all of the above
ANSWER : : all of the above
21.Directional relays are based on flow of
power
current
voltage wave
all of the above
ANSWER : : power
22.Arc in a circuit behaves as
a capackive reactance
an inductive reactance
a resistance increasing with voltage rise across the arc
a resistance decreasing with voltage rise across the arc
ANSWER : : a resistance decreasing with voltage rise across the arc
23.Overload relays are of…… type.
induction
solid state
thermal & electromagnetic
all above
ANSWER : : all above
24.With which of the following, a circuit breaker must be equipped for remote operation ?
Inverse time trip
Time-delay trip
Shunt trip
None of the above
ANSWER : : Shunt trip
25.H.R.C. fuses provide best protection against
overload
reverse current
open-circuits
short-circuits
ANSWER : : short-circuits
26.Resistance grounding is used for voltage between
33kVto66kV
HkVto33kV
3.3kVandllkV
none of the above
ANSWER : : 3.3kVandllkV
27.The contacts of high voltage switches used in power system are submerged in oil. The main purpose of the oil is to
lubricate the contacts
insulate the contacts from switch body
extinguish the arc
all of the above
ANSWER : : extinguish the arc
28.The voltage appearing across the contacts after opening of the circuit breaker is called______voltage.
recovery
surge
operating
arc
ANSWER : : recovery
29.For the protection of power station buildings against direct strokes the requirements are
interception
interception and conduction
interception, conduction and dis-sipation
interception, conduction, dissipation and reflection
ANSWER : : interception, conduction and dis-sipation
30.Large internal faults are protected by
merz price percentage differential protection
mho and ohm relays
horn gaps and temperature relays
earth fault and positive sequence relays
ANSWER : : merz price percentage differential protection
31.Ionization in circuit breaker is facilitated by
high temperature
increase of mean free path
increasing field strength
all of the above
ANSWER : : all of the above
32.The ground wire should not be smaller than No ______ copper.
2
4
6
10
ANSWER : : 10
33.The interaction between a transmission line and communication line js minimized by
transposing transmission as well as communication lines
increasing the height of the trans-mission line tower
increasing the distance between the two lines
all of the above
ANSWER : : all of the above
34.Overheating of relay contacts or contact born out is due to
slow making and breaking of load circuit contacts
foreign matter on the contact surface
too low contact pressure
all of the above
ANSWER : : all of the above
35.In a circuit breaker the basic problem is to
maintain the arc
extinguish the arc
transmit large power
emit the ionizing electrons
ANSWER : : transmit large power
36.The time of closing the cycle, in modern circuit breakers is
0.003 sec
0.001 sec
0.01 sec
0.10 sec
ANSWER : : 0.003 sec
37.Shunt capacitance is neglected while considering
short transmission line
medium transmission line
long transmission line
medium and long transmission lines
ANSWER : : short transmission line
38.The arc voltage produced in A.C. circuit breaker is always
in phase with the arc current
lagging the arc current by 90″
leading the arc current by 90�
none of the above
ANSWER : : in phase with the arc current
39.The delay fuses are used for the protection of ________ .
motors
power outlet circuits
fluorescent lamps
light circuits
ANSWER : : motors
40.When a transmission line is energized, the wave that propagates on it is
current wave only
voltage wave only
both (a) and (b)
power factor wave only
ANSWER : : both (a) and (b)
41.Insulation resistance of high voltage circuit breakers is more than
1 mega ohms
10 mega ohms
100 mega ohms
500 mega ohms
ANSWER : : 100 mega ohms
42.Wave trap is used to trap waves of
power frequencies
higher frequencies entering genera�tor or transformer units
either of the above
none of the above
ANSWER : : higher frequencies entering genera�tor or transformer units
43.Interruption of large currents by relay requires
arc suppressing blow out coils
wide separation of the opened contacts
high speed opening of contacts
all of the above
ANSWER : : all of the above
44.The reflection co-efficient at the open circuited end of a transmission line.
zero
infinity
unity
none of the above
ANSWER : : unity
45.Which of the following is the least expensive protection for overcurrent is low voltage system ?
Rewireable fuse
Isolator
Oil circuit breaker
Air break circuit breaker
ANSWER : : Rewireable fuse
46.To protect most of the electrical equipment handling low power, the types of relays used are
thermocouple
electronic and bimetallic
both (a) and (b)
none of the above
ANSWER : : both (a) and (b)
47.Protective relays are devices that detect abnormal conditions in electrical circuits by measuring
current during abnormal condition
voltage during abnormal condition
constantly the electrical quantities which differ during normal and abnormal conditions
none of the above
ANSWER : : constantly the electrical quantities which differ during normal and abnormal conditions
48.Ungrounded neutral transmission system is not recommended because of system
insulation being overstressed due to pver voltages
insulation overstress may lead to failure and subsequent phase to phase faults
being inadequately protected against ground fault
all of the above
ANSWER : : all of the above
49.Distance relays are generally
split-phase relays
reactance relays
impedance relays
none of the above
ANSWER : : none of the above
50.Which of the following parameter can be neglected for a short line ?
Inductance
Capacitance
Resistance
Reactance
ANSWER : : Capacitance
51.Discrimination between main and back up protection is provided by the use of relays which are
fact
sensitive
slow
none of the above
ANSWER : : slow
52.The short circuit in any winding of the transformer is the result of
mechanical vibration
insulation failure
loose connection
impulse voltage
ANSWER : : impulse voltage
53.The relay with inverse time characteristic will operate within
1.5 sec
5 to 10 sec
5 to 20 sec
20 to 30 sec
ANSWER : : 5 to 10 sec
54.Which of the following circuit breakers has high reliability and minimum maintenance ?
Air blast circuit breakers
Circuit breaker with SF6 gas
Vacuum circuit breakers
Oil circuit breakers
ANSWER : : Circuit breaker with SF6 gas
55.Arc in a circuit breaker is interrupted at
zero current
maximum current
minimum voltage
maximum voltage
ANSWER : : zero current
56.For which of the following protection from negative sequence currents is provided ?
Generators
Motors
Transmission line
Transformers
ANSWER : : Generators
57.Which of the following statements is incorrect ?
Lightning arrestors are used before the switchgear
Shunt reactors are used as compensation reactors
The peak short current is (1.8 xV2) times the A.C. component
The MVA at fault is equal to base MVA divided by per unit equivalent fault reactance
ANSWER : : Lightning arrestors are used before the switchgear
59.A.C. network analyser is used to solve problems of
load flow
load flow and short-circuit
load flow and stability
load flow, short-circuit and stability
ANSWER : : load flow, short-circuit and stability
60.What will be the reflection co-efficient of the wave of load connected to transmission line if surge impedance of the line is equal to load ?
Zero
Unity
Infinity
None of the above
ANSWER : : Zero
61.Which of the following devices will receive voltage surge first travelling on the transmission line ?
Lightning arresters
Relays
Step-down transformer
Switchgear
ANSWER : : Lightning arresters
62.Which of the following statements is incorrect?
Station batteries are used to operate relay only
The lightning arresters are basically surge diverters
An impedance relay has maximum fault current when fault occurs near the relay
A high speed relay has an operation of 1 to 2 cycles
ANSWER : : Station batteries are used to operate relay only
63.To reduce short circuit fault currents are used.
reactors
resistors
capacitors
none of the above
ANSWER : : reactors
64.Induction cup relay is operated due to changes in
current
voltage
impedance
all of the above
ANSWER : : all of the above
65.The single phasing relays are used for the protection of
single phase motors only
two phase motors only
two single phase motors running in parallel
three phase motors
ANSWER : : three phase motors
66.Series reactors should have
low resistance
high resistance
low impedance
high impedance
ANSWER : : low resistance
67.For cost and safety, the outdoor substa tions are installed for voltages above
11 kV
33 kV
60kV
110kV
ANSWER : : 33 kV
68.For which of the following ratings of the transformer differential protection is recommended ?
above 30 kVA.
equal to and above 5 MVA
equal to and above 25 MVA
none of the above
ANSWER : : equal to and above 5 MVA
69.A _______ is used to measure the stator % winding temperature of the generator.
thermocouple
pyrometer
resistance thermometer
thermometer
ANSWER : : resistance thermometer
70.An isolator is installed
to operate the relay of circuit breaker
as a substitute for circuit breaker
always independent of the position of circuit breaker
generally on both sides of a circuit breaker
ANSWER : : generally on both sides of a circuit breaker
71.Admittance relay is _______ relay.
impedance
directional
non-directional
none of the above
ANSWER : : directional
72.On which of the following effects of electric current a fuse operates ?
Photoelectric effect
Electrostatic effect
Heating effect
Magnetic effect
ANSWER : : Heating effect
73.The steady state stability of the power system can be increased by
connecting lines in parallel
connecting lines in series
using machines of high impedance
reducing the excitation of machines
ANSWER : : connecting lines in parallel
74.The material used for fuse must have
low melting point and high specific resistance
low melting point and -low specific resistance
high melting point and low specific resistance
low melting point and any specific resistance
ANSWER : : low melting point and high specific resistance
75.A fuse in a motor circuit provides protection against
overload
short-circuit and overload
open circuit, short-circuit and overload
none of the above
ANSWER : : short-circuit and overload
76.The fuse rating is expressed in terms of
current
voltage
VAR
kVA
ANSWER : : current
77.H.R.C. fuse, as compared to a rewirable fuse, has
no ageing effect
high speed of operation
high rupturing capacity
all of the above
ANSWER : : all of the above
78.A fuse is connected
in series with circuit
in parallel with circuit
either in series or in parallel with circuit
none of the above
ANSWER : : in series with circuit
79.By which of the following methods major portion of the heat generated in a H.R.C. fuse is dissipated ?
Radiation
Convection
Conduction
All of the above
ANSWER : : Conduction
80.Series capacitors are used to
compensate for line inductive reactance
compensate for line capacitive reactance
improve line voltage
none of the above
ANSWER : : compensate for line inductive reactance
81.Overfluxing protection is recommended for
distribution transformer
generator transformer of the power plant
auto-transformer of the power plant
station transformer of the power plant
ANSWER : : generator transformer of the power plant
82.Air blast circuit breakers for 400 kV power system are designed to operate in
100 micro-second
50 milli-second
0.5 sec
0.1 sec
ANSWER : : 50 milli-second
83.If the fault occurs near the impedance relay, the VII ratio will be
constant for all distances
lower than that of if fault occurs away from the relay
higher than that of if fault occurs away from the relay
none of the above
ANSWER : : lower than that of if fault occurs away from the relay
84.The inductive interference between power and communication line can be minimized by
transposition of the power line
transposition of the communication line
both (a) and (b)
increasing the distance between the conductors
ANSWER : : both (a) and (b)
85.A fuse is never inserted in
neutral wire
negative of D.C. circuit
positive of D.C. circuit
phase dine
ANSWER : : neutral wire
86.The torque produced in induction type relay (shaded pole structure) is
inversely proportional to the current
inversely proportional to the square of the current
proportional to the current
proportional to square of the current
ANSWER : : inversely proportional to the square of the current
88.A switchgear is device used for
interrupting an electrical circuit
switching an electrical circuit 111.
switching and controlling an electri�cal circuit
switching, controlling and protect�ing the electrical circuit and equipment
ANSWER : : switching, controlling and protect�ing the electrical circuit and equipment
89.The power loss is an important factor for the design of
transmission line
motor
generator
feeder
ANSWER : : transmission line
90.Over voltage protection is recommended for
hydro-electric generators
steam turbine generators
gas turbine generators
all of the above
ANSWER : : all of the above
91.The fuse wire, in D.C. circuits, is inserted in
negative circuit only
positive circuit only
both (a) and (b)
either (a) or (b)
ANSWER : : both (a) and (b)
92.Oil switches are employed for
low currents circuits
low voltages circuits
high voltages and large currents circuits
all circuits
ANSWER : : high voltages and large currents circuits
93.Protection by fuses is generally not used beyond
20 A
50 A
100 A
200 A
ANSWER : : 100 A
94.The fuse blows off by
burning
arcing
melting
none of the above
ANSWER : : melting
95.In a single bus-bar system there will be complete shut down when
fault occurs on the bus itself
fault occurs on neutral line
two or more faults occur simultaneously
fault occurs with respect to earthing
ANSWER : : fault occurs on the bus itself
96.The information to the circuit breaker under fault conditions is provided by
relay
rewirable fuse
H.R.C. only
all of the above
ANSWER : : relay
97.To limit short-circuit current in a power system are used.
earth wires
isolators
H.R.C. fuses
reactors
ANSWER : : reactors
98.A balanced 3-phase system consists of
zero sequence currents only
positive sequence currents only
negative and zero sequence currents
zero, negative and positive sequence currents
ANSWER : : positive sequence currents only