If you think you have a good understanding of Power System Protection Fundamentals, challenge yourself and take our quiz.
Best of Luck.!!
Question 1 of 80
Q.1 What is the function of relay?
Detects abnormal condition
Breaks the circuit
Both
Question 2 of 80
Q.2 What type of CT is used in relay circuits?
Protection CT
Measurement CT
Both can be used
Question 3 of 80
Q.3 If a system encounters a fault near its distribution side but the relay at generation side trips, which factor of relay design needs to be configured?
Reliability
Selectivity
Sensitivity
New Choice
Question 4 of 80
Q.4 If the current in the system rises due to increase in load but the relay trips considering it as fault, which factor needs to be adjusted?
Speed
Question 5 of 80
Q.5 The factor of relay design which says that relay should trip before causing damage to any equipment is:
Question 6 of 80
Q.6 Which relay should be used in a ring system?
Differential relay
Directional relay
Distance relay
Question 7 of 80
Q.7 To detect the fault in a transmission line, which relay is the most suitable?
Question 8 of 80
Q.8 Which one is the trip setting for directional relay?
Only high current
Low current setting and direction
High current setting and direction
Question 9 of 80
Q.9 Which additional setting do we need in an inverse time relay as compared to definite time relay?
Current setting
Time setting
Curve setting
Question 10 of 80
Q.10 Which type of system does not require a directional relay?
Radial system
Parallel system
Ring main system
Question 11 of 80
Q.11 In which condition the distance relay will not work?
High impedance fault
When fault is at the edge of protection region
Both ‘a’ and ‘b’
Question 12 of 80
Q.12 With which components of power system, reverse power relay can be used?
Generators connected in parallel
Transmission lines
Motors
Question 13 of 80
Q.13 Which relay has the smallest protection region?
Over current relay
Question 14 of 80
Q.14 At both terminals, in which parameter differential relay detects the change?
Magnitude of current
Phase of current
Question 15 of 80
Q.15 If a breaker fails to isolate the fault, which breaker should operate next?
Upstream breaker
Downstream breaker
Breaker present on the same bus
Question 16 of 80
Q.16 Why do we need to coordinate the protection devices?
To limit the area affected by fault
To protect equipment
No particular reason
Question 17 of 80
Q.17 For proper coordination of protection devices. Upstream breaker should be of
Equal rating as of the downstream breaker
Lower rating than the downstream breaker
Higher rating than the downstream breaker
Question 18 of 80
Q.18 The reference for breaker sizing should be
Upstream breakers
Downstream breakers
Question 19 of 80
Q.19 Why can’t we use definite time relays for protection of power system?
Upstream breaker needs quick trip time
Downstream breaker needs quick trip time
Question 20 of 80
Q.20 What is the relation between current and time in definite time relay?
Inverse
Direct
None
Question 21 of 80
Q.21 Why do we need inverse time relay?
It isolates the fault instantly
It maintains coordination along with adjusting the trip time according to fault current
Question 22 of 80
Q.22 What type of relay has inverse relation between current and time?
Definite Time Relay
Instantaneous Relay
Inverse Time Relay
Question 23 of 80
Q.23 Why is the upstream beakers curve set for higher current and time values as compare to the downstream breaker?
To incorporate the timing of downstream breaker
Because fault current increases towards upstream
Question 24 of 80
Q.24 Which parameter shifts the trip time curve on x-axis.
Time
Current
Voltage
Question 25 of 80
Q.25 Time of trip shifts the trip time curve on?
X-axis
Y-axis
No change
Question 26 of 80
Q.26 Why do we need different trip time for breakers present in different regions even for extremely high fault current values?
To make the system reliable
To prevent power outage of a greater region
To allow downstream region to isolate the fault first
Question 27 of 80
Q.28 Why are single line to ground and double line to ground faults categorized as unbalanced faults?
Because they do not occur in all three line
Because they give rise to unequal currents in lines
Because they are grounded
Question 28 of 80
Q.29 A symmetrical fault should have?
Equal phase
Equal increment in current value
Question 29 of 80
Q.30 Why do we use per unit system in fault calculations?
To bring the system on a single value, based on a single base
To eliminate differences in values of parameters in different zones of system
No reason in specific
Question 30 of 80
Q.31 What is the cause the negative sequence current in power system?
Ground current
Unbalanced current
Flow of current in opposite direction
Question 31 of 80
Q.32 Zero sequence current can be prevented
When the system has no ground connection
When the system has shunt reactors
Can never be prevented
Question 32 of 80
Q.33 Do per unit values have any units?
Same as normal values
There are other units
No units
Question 33 of 80
Q.34 How many bases do we need to proceed with the calculations?
All
At least one
At least two
Question 34 of 80
Q.35 Which parameter should have same base value in all zones?
Power
Question 35 of 80
Q.36 Generator only feeds
Positive sequence current
Negative sequence current
Zero sequence current
Question 36 of 80
Q.37 Why do we represent delta side of transformer as open circuit in case of zero sequence network?
Because it has no ground
Because it does not let zero sequence current flow through it
Question 37 of 80
Q.38 Which connection of transformer allows the zero-sequence current to flow?
Wye connection with solid grounding
Wye connection with reactance grounding
Both a & b
Question 38 of 80
Q.39 Why do we only have positive sequence current in a three phase to ground fault?
Because it has ground
Because it is symmetrical fault
Because it is unsymmetrical fault
Question 39 of 80
Q.40 Which matrix is used to calculate phase current or voltage values?
Transpose matrix
Transformation matrix
Linear matrix
Question 40 of 80
Q.41 What is the relation between sequence currents in case of single line to ground fault?
All sequence currents have equal magnitude
Zero sequence has different magnitude
All sequence currents have different magnitudes
Question 41 of 80
Q.42 How are the sequence networks (positive, negative and zero) modelled in a sequence circuit in case of a single line to ground fault?
All sequence networks are in parallel
All sequence networks are in series
Positive and negative sequence networks are in parallel
Question 42 of 80
Q.43 Why are the voltages in unfaulted lines are out of phase in case of single line to ground fault?
Because the voltage of phase with no fault is zero
To maintain the phase balance
Question 43 of 80
Q.44 What are the values of voltages in case of single line to ground fault?
Same volts for unfaulted phases
Zero volts for faulted phase
Question 44 of 80
Q.45 Why do we only have positive and negative sequence in line-to-line fault?
Because the phases are short circuited and current circulates
The fault is not grounded
No specific reason
Question 45 of 80
Q.46 Fault current in both the lines in a line-to-line fault have
Same magnitude, opposite phase
Same magnitude, same phase
Different magnitude, same phase
Question 46 of 80
Q.47 How are the sequence networks connected in case of line-to-line fault?
All in parallel
All in series
Positive and negative in parallel
Question 47 of 80
Q.48 Why are positive and negative sequence modelled in parallel in a line-to-line fault?
Because of a closed path.
Because both the currents have same magnitude but are in opposite direction
Question 48 of 80
Q.49 What would be the value of voltage on lines with line-to-line fault?
Double the original value
Half the original value
Question 49 of 80
Q.50 How are the sequence networks connected in case of double line to ground fault?
Question 50 of 80
Q.51 Fault current in both the phases in a double line to ground fault have
Same magnitude, different phase
Question 51 of 80
Q.52 In double line to ground fault, the sequence voltages are such that
All are equal
All are unequal
Only two are equal
Question 52 of 80
Q.53 To account for the change in magnitude of voltage from LV side to HV side, which parameter is changed?
The formula
Base value of power
Base value of voltage
Question 53 of 80
Q.54 In which case do we have to incorporate phase change in voltage when moving from LV side to HV side?
When transformer connections are delta-wye
When transformer connections are wye-wye
When transformer connections are delta-delta
Question 54 of 80
Q.55 Why do we have the negative sequence Infront or ahead of a reference point, when the positive sequence is behind that reference point?
Because negative sequence leads
Because negative sequence rotates in opposite direction
Question 55 of 80
Q.56 Which quantities do not change by changing the zone in the system?
Base power
Both a & c
Per unit values
Question 56 of 80
Q.57 How do we account for the phase change in positive sequence current when moving from LV side to HV side?
Multiplying ‘j’
Multiplying ‘a’
Depends on transformer connection
Question 57 of 80
Q.58 By moving from LV side to HV side, we multiply by 1<-30° in case of
Question 58 of 80
Q.59 Why do we observe a voltage depression in one of the unfaulted phases on HV side in case of delta connection?
Because of nature of fault
Because of transformer connections
Question 59 of 80
Q.60 Why is the zero-sequence current nonexistent in line-to-line fault?
Because it is unsymmetrical
Because there is no ground
Question 60 of 80
Q.61 Why are all the line voltages on HV side differently effected in case of line-to-line fault?
Question 61 of 80
Q.62 In a given waveform, which parameters can be used to identify the type of fault?
Current and voltage waveforms
Sequence current waveforms
Question 62 of 80
Q.63 How do we identify the type of fault by using sequence currents?
By identifying which sequence currents are present and their magnitude
By identifying which sequence currents are present and their phase
Question 63 of 80
Q.64 Which relay parameters can be identified by the given fault waveform?
Pick up current
Time of operation
Curve slope
Question 64 of 80
Q.65 Can we identify the type of relay from the fault analysis waveform?
Yes, in all cases
No, it cannot be identified
Yes, but it depends on the given case
Question 65 of 80
Q.66 What is the phase difference between line currents of the faulted phases in case of line-to-line fault?
120 degrees
180 degrees
90 degrees
Question 66 of 80
Q.67 Why are the fault currents not symmetrical in case of double line to ground fault?
Because of the ground
Because it has zero sequence current
Fault currents are symmetrical
Question 67 of 80
Q.68 How can we identify the positive sequence network from the given sequence network diagrams?
By identifying a source
By identifying an open circuit due to transformer connection
Have no source
Question 68 of 80
Q.69 What type of transformer connections can help us in identifying the zero-sequence network?
Delta-wye
Delta-delta
Question 69 of 80
Q.70 Why do we need symmetrical components?
To calculate balanced faults
To calculate unbalanced faults
To calculate bolted faults
Question 70 of 80
Q.71 Which conditions should be verified in order to find out whether a set of phasors is symmetrical or not?
Equal magnitude
Equal phase angle
Question 71 of 80
Q.72 Which sequence should be followed by phasors in order to assure symmetry?
ABC
ACB
Question 72 of 80
Q.73 What is the difference between ABC system and ACB system?
Phase sequence
Phasor magnitudes
Phase angles
Question 73 of 80
Q.74 How many symmetrical components are generated from a single set of unbalanced phasors?
1
3
6
Question 74 of 80
Q.75 What is the sequence of symmetrical components when the unbalanced phasors have ACB phase sequence?
Positive= ACB; Negative=ACB; Zero=none
Positive= ACB; Negative=ABC; Zero=none
Positive= ABC; Negative=ACB; Zero=none
Question 75 of 80
Q.76 What would be the resultant when we add all three symmetrical components respectively?
A balanced set of phasors
The original unbalanced set of phasors
A different set of phasors
Question 76 of 80
Q.77 How many symmetrical components are generated from a single set of balanced phasors?
Question 77 of 80
Q.78 Why do we need ‘a’ operator?
To define all phasors in terms of one
It is present in the formula
Question 78 of 80
Q.79 Is the ‘a’ operator sequence specific? (different for ABC and ACB phase sequence?)
Yes, in some cases
No
Question 79 of 80
Q.80 What is the benefit of using ‘a’ operator?
Decreases number of variables
Reduces equation complexity
Question 80 of 80
Q.81 How can we find symmetrical components from System phasors?
Iₛᵧₘₘₑₜᵣᵢ꜀ₐₗ = A * Iₛᵧₛₜₑₘ
Iₛᵧₘₘₑₜᵣᵢ꜀ₐₗ = A⁻¹ * Iₛᵧₛₜₑₘ
Iₛᵧₘₘₑₜᵣᵢ꜀ₐₗ = Iₛᵧₛₜₑₘ / A