WorksheetsPower System RASL Activity 6
Total questions: 40
Worksheet time: 20mins
which of these are symmetrical fault
L-G
L-L-G
L-L
L-L-L
The component which provides a signal to circuit breaker under the fault condition:
Isolator
Fuse
Relay
CT
The correct statement about Buchholz relay
It can only be used with largely sized alternators
It is installed with largely sized transformers which have no conservator tank
It can detect incipient faults
It should never be used with oil immersed transformers
Buchholz relay is used to protect:
ALTERNATOR
INDUCTION MOTOR
SYNCHRONOUS MOTOR
TRANSFORMER
____________________ is/are an instantaneous relay/s:
PMMC type
Shaded pole type
Both of these
None of these
Plug setting multiplier is defined as the ratio of:
Fault current in relay coil x Pick up current
Fault current in relay coil / Pick up current
Fault current in relay coil x Transformer secondary turns
Fault current in relay coil / Transformer secondary turns
High-speed circuit breakers result in:
Increased stability of power systems
decreased stability of power systems
The basic purpose of a relay is to:
Detect the fault
Remove the fault
Trip the circuit
All of these
In Electrical power protection schemes ______________ transformer is used:
VT
CAPACITIVE VOLTAGE TRANFORMER
Both of these
None of these
The equipment which has lowest chances of fault occurrence:
Alternator
Transformer
Switchgear
Induction motors
A definite time relay is ___________ the amount of current:
Dependent on
Independent of
The extent of damage and injuries caused due to a shock depends on:
Amount of current
Path of the current
Time for which current flows
All of these
Backup protection is installed to:
Increase the protection reliability of the system
To increase the speed of protection system
Both of these
None of these
station type LA can discharge current of
>100kA
<100kA and >65kA
<65kA
none
In which part of the power system has lowest voltage?
Generation
Distribution
Transmission
Grid
Transmission line usually have highest voltage in the components of power system.
True
False
How will you calculate the Per unit value?
Base value/Actual value
Actual value/Per unit value
Per unit value/Actual value
Actual value/Base value
Base impedance of the power system is given as:
(Base kV)2/Base MVA
(Base kV)/Base MVA
Base MVA/(Base kV)2
None of these
A generator is rated of of 10 MVA, and 33 kV. The base impedance will be
2089 ohm
100 ohm
1089 ohm
4089 ohm
The unit for base impedance is in .......... ohm
True
False
Use of high speed circuit breaker will actually increase the system stability.
False
True
Which one of the following device is used for improving the power factor of the system:
Synchronous Phase Modifier
Shunt Reactor
Series Reactor
Asynchronous Generator
In a transmission line system, the feeders act as input to _________
a) distributors
b) service mains
c) transformer sub stations
d) all of the mentioned
Which sequence this ?
Positive sequence
Negative sequence
Zero sequence
All
The operator a^2 is
-0.5+j0.866
-0.5-j0.866
-1+j0.5
-1-j0.5
If a positive sequence current passes through a transformer and its phase shift is 30 degrees, the negative sequence current flowing through the transformer will have a phase shift of
30 deg
-30deg
120 deg
-120 deg
The zero sequence impedances of an ideal star-delta connected transformer (star-grounded)
looking from star side is zero and looking from delta side is infinite
looking from star side is zero and looking from delta side is also zero
looking from star side is infinite and looking from delta side is zero
looking from star side is infinite and looking from delta side is zero
What is the value of zero sequence impedance in line to line faults?
Z0 = 1
Z0 = ∞
Z0 = 3 Zn
Z0 = 0
Which among these is the connection diagram for line to line faults?
only a
only b
only c
only d
What is the expression for fault current in line to line fault?
If = √3 * (Ea / Z1 + Z2)
If = 3 * (Ea / Z1 + Z2)
If = √3 * (Ea / Z1 + Z2 + Z0)
If = 3 * (Ea / Z1 + Z2 + Z0)
What are the terminal conditions in case of SLG fault, if the fault occurs in the phase A?
Vb = 0, Ia = 0, Ic = 0
Va = 0, Ib = 0, Ic = 0
Va = 0, Ia = 0, Ic = 0
Vb = 0, Ia = 0, Ib = 0
What percentage of faults occurring is single line to ground fault?
50 %
60 %
35 %
70 %
What are the types of unsymmetrical faults?
Single line to ground fault
Double line to ground fault
Line to line fault
All of these
Positive, negative and zero sequence impedances of line are 2,2 and 5 pu respectively. Find self and mutual impedances respectively?
1 and 3 pu
3 and 1 pu
2 and 2 pu
2 and 5 pu
A transmission line has self and mutual impedances are 0.8 and 0 pu respectively. Find the positive, negative and zero sequence impedances respectively?
0.6, 0.8 and 1.2 pu
0.6, 0.6 and 1.2 pu
0.6, 0.6 and 0.6 pu
0.8, 0.8 and 0.8 pu
For symmetrical network, the neutral current is
zero
infinity
maximum
any of the above
The positive, negative and zero sequence impedances of a transmission line are 0.5,0.5 and 1.1 pu respectively. The self (Zs) and mutual (Zm) impedances of the line will be given by
Zs = 0.7 pu, Zm =0.2 pu
Zs = 0.5 pu, Zm =0.6 pu
Zs = 0.6 pu, Zm =0.5 pu
Zs = 0.2 pu, Zm =0.7 pu
If all the sequence voltages at the fault point in a power system are equal, then the fault point is a
LLL
LL
LG
LLG
The zero sequence current of a generator for line to ground fault is j3 pu. Then the current through the neutral during the fault is
j3 pu
j1 pu
j9 pu
j6 pu
Which of the following statement is/are true?Zn
The neutral grounding impedance Zn appears as 3Zn in zero sequence equivalent circuit
The neutral grounding impedance Zn appears as Zn in zero sequence equivalent circuit
both 1 and 2
nether 1 nor 2
