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# MCQ's Power System Protection Fundamentals Assessment

This Power System Course aims to teach you the fundamentals of power system protection, it makes the tedious and complex calculations done in power system studies easy for you to understand. If you think you have a good understanding of Power System Protection, challenge yourself and take our quiz.

Question 1 of 80

# Q.1 What is the function of relay?

A

Detects abnormal condition

B

Breaks the circuit

C

Both

Question 2 of 80

A

Protection CT

B

Measurement CT

C

Both can be used

Question 3 of 80

A

Reliability

B

Selectivity

C

Sensitivity

D

New Choice

Question 4 of 80

A

Speed

B

Reliability

C

Sensitivity

Question 5 of 80

A

Speed

B

Reliability

C

Sensitivity

Question 6 of 80

# Q.6 Which relay should be used in a ring system?

A

Differential relay

B

Directional relay

C

Distance relay

Question 7 of 80

# Q.7 To detect the fault in a transmission line, which relay is the most suitable?

A

Differential relay

B

Directional relay

C

Distance relay

Question 8 of 80

# Q.8 Which one is the trip setting for directional relay?

A

Only high current

B

Low current setting and direction

C

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?

A

Current setting

B

Time setting

C

Curve setting

Question 10 of 80

# Q.10 Which type of system does not require a directional relay?

A

B

Parallel system

C

Ring main system

Question 11 of 80

# Q.11 In which condition the distance relay will not work?

A

High impedance fault

B

When fault is at the edge of protection region

C

Both ‘a’ and ‘b’

Question 12 of 80

# Q.12 With which components of power system, reverse power relay can be used?

A

Generators connected in parallel

B

Transmission lines

C

Motors

Question 13 of 80

# Q.13 Which relay has the smallest protection region?

A

Over current relay

B

Distance relay

C

Differential relay

Question 14 of 80

# Q.14 At both terminals, in which parameter differential relay detects the change?

A

Magnitude of current

B

Phase of current

C

Both

Question 15 of 80

# Q.15 If a breaker fails to isolate the fault, which breaker should operate next?

A

Upstream breaker

B

Downstream breaker

C

Breaker present on the same bus

Question 16 of 80

# Q.16 Why do we need to coordinate the protection devices?

A

To limit the area affected by fault

B

To protect equipment

C

No particular reason

Question 17 of 80

# Q.17 For proper coordination of protection devices. Upstream breaker should be of

A

Equal rating as of the downstream breaker

B

Lower rating than the downstream breaker

C

Higher rating than the downstream breaker

Question 18 of 80

# Q.18 The reference for breaker sizing should be

A

Upstream breakers

B

Downstream breakers

C

Both

Question 19 of 80

# Q.19 Why can’t we use definite time relays for protection of power system?

A

Upstream breaker needs quick trip time

B

Downstream breaker needs quick trip time

C

Both

Question 20 of 80

# Q.20 What is the relation between current and time in definite time relay?

A

Inverse

B

Direct

C

None

Question 21 of 80

# Q.21 Why do we need inverse time relay?

A

It isolates the fault instantly

B

It maintains coordination along with adjusting the trip time according to fault current

C

None

Question 22 of 80

# Q.22 What type of relay has inverse relation between current and time?

A

Definite Time Relay

B

Instantaneous Relay

C

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?

A

To incorporate the timing of downstream breaker

B

Because fault current increases towards upstream

C

Both

Question 24 of 80

# Q.24 Which parameter shifts the trip time curve on x-axis.

A

Time

B

Current

C

Voltage

Question 25 of 80

# Q.25 Time of trip shifts the trip time curve on?

A

X-axis

B

Y-axis

C

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?

A

To make the system reliable

B

To prevent power outage of a greater region

C

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?

A

Because they do not occur in all three line

B

Because they give rise to unequal currents in lines

C

Because they are grounded

Question 28 of 80

# Q.29 A symmetrical fault should have?

A

Equal phase

B

Equal increment in current value

C

Both

Question 29 of 80

# Q.30 Why do we use per unit system in fault calculations?

A

To bring the system on a single value, based on a single base

B

To eliminate differences in values of parameters in different zones of system

C

No reason in specific

Question 30 of 80

# Q.31 What is the cause the negative sequence current in power system?

A

Ground current

B

Unbalanced current

C

Flow of current in opposite direction

Question 31 of 80

# Q.32 Zero sequence current can be prevented

A

When the system has no ground connection

B

When the system has shunt reactors

C

Can never be prevented

Question 32 of 80

# Q.33 Do per unit values have any units?

A

Same as normal values

B

There are other units

C

No units

Question 33 of 80

# Q.34 How many bases do we need to proceed with the calculations?

A

All

B

At least one

C

At least two

Question 34 of 80

# Q.35 Which parameter should have same base value in all zones?

A

Power

B

Voltage

C

Current

Question 35 of 80

# Q.36 Generator only feeds

A

Positive sequence current

B

Negative sequence current

C

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?

A

Because it has no ground

B

Because it does not let zero sequence current flow through it

C

Both

Question 37 of 80

# Q.38 Which connection of transformer allows the zero-sequence current to flow?

A

Wye connection with solid grounding

B

Wye connection with reactance grounding

C

Both a & b

Question 38 of 80

# Q.39 Why do we only have positive sequence current in a three phase to ground fault?

A

Because it has ground

B

Because it is symmetrical fault

C

Because it is unsymmetrical fault

Question 39 of 80

# Q.40 Which matrix is used to calculate phase current or voltage values?

A

Transpose matrix

B

Transformation matrix

C

Linear matrix

Question 40 of 80

# Q.41 What is the relation between sequence currents in case of single line to ground fault?

A

All sequence currents have equal magnitude

B

Zero sequence has different magnitude

C

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?

A

All sequence networks are in parallel

B

All sequence networks are in series

C

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?

A

Because the voltage of phase with no fault is zero

B

To maintain the phase balance

C

Both a & b

Question 43 of 80

# Q.44 What are the values of voltages in case of single line to ground fault?

A

Same volts for unfaulted phases

B

Zero volts for faulted phase

C

Both

Question 44 of 80

# Q.45 Why do we only have positive and negative sequence in line-to-line fault?

A

Because the phases are short circuited and current circulates

B

The fault is not grounded

C

No specific reason

Question 45 of 80

# Q.46 Fault current in both the lines in a line-to-line fault have

A

Same magnitude, opposite phase

B

Same magnitude, same phase

C

Different magnitude, same phase

Question 46 of 80

# Q.47 How are the sequence networks connected in case of line-to-line fault?

A

All in parallel

B

All in series

C

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?

A

Because of a closed path.

B

Because both the currents have same magnitude but are in opposite direction

C

None

Question 48 of 80

# Q.49 What would be the value of voltage on lines with line-to-line fault?

A

Double the original value

B

Half the original value

C

No change

Question 49 of 80

# Q.50 How are the sequence networks connected in case of double line to ground fault?

A

All in parallel

B

All in series

C

Positive and negative in parallel

Question 50 of 80

# Q.51 Fault current in both the phases in a double line to ground fault have

A

Same magnitude, different phase

B

Same magnitude, same phase

C

Different magnitude, same phase

Question 51 of 80

# Q.52 In double line to ground fault, the sequence voltages are such that

A

All are equal

B

All are unequal

C

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?

A

The formula

B

Base value of power

C

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?

A

When transformer connections are delta-wye

B

When transformer connections are wye-wye

C

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?

A

B

Because negative sequence rotates in opposite direction

C

None

Question 55 of 80

# Q.56 Which quantities do not change by changing the zone in the system?

A

Base power

B

Both a & c

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?

A

Multiplying ‘j’

B

Multiplying ‘a’

C

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

A

Positive sequence current

B

Negative sequence current

C

Zero sequence current

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?

A

Because of nature of fault

B

Because of transformer connections

C

None

Question 59 of 80

# Q.60 Why is the zero-sequence current nonexistent in line-to-line fault?

A

Because it is unsymmetrical

B

Because there is no ground

C

Both

Question 60 of 80

# Q.61 Why are  all the line voltages on HV side differently effected in case of line-to-line fault?

A

Because of nature of fault

B

Because of transformer connections

C

None

Question 61 of 80

# Q.62 In a given waveform, which parameters can be used to identify the type of fault?

A

Current and voltage waveforms

B

Sequence current waveforms

C

Both

Question 62 of 80

# Q.63 How do we identify the type of fault by using sequence currents?

A

By identifying which sequence currents are present and their magnitude

B

By identifying which sequence currents are present and their phase

C

Both

Question 63 of 80

# Q.64 Which relay parameters can be identified by the given fault waveform?

A

Pick up current

B

Time of operation

C

Curve slope

Question 64 of 80

# Q.65 Can we identify the type of relay from the fault analysis waveform?

A

Yes, in all cases

B

No, it cannot be identified

C

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?

A

120 degrees

B

180 degrees

C

90 degrees

Question 66 of 80

# Q.67 Why are the fault currents not symmetrical in case of double line to ground fault?

A

Because of the ground

B

Because it has zero sequence current

C

Fault currents are symmetrical

Question 67 of 80

# Q.68 How can we identify the positive sequence network from the given sequence network diagrams?

A

By identifying a source

B

By identifying an open circuit due to transformer connection

C

Have no source

Question 68 of 80

# Q.69 What type of transformer connections can help us in identifying the zero-sequence network?

A

Delta-wye

B

Delta-delta

C

Both a & b

Question 69 of 80

# Q.70 Why do we need symmetrical components?

A

To calculate balanced faults

B

To calculate unbalanced faults

C

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?

A

Equal magnitude

B

Equal phase angle

C

Both

Question 71 of 80

# Q.72 Which sequence should be followed by phasors in order to assure symmetry?

A

ABC

B

ACB

C

Both

Question 72 of 80

# Q.73 What is the difference between ABC system and ACB system?

A

Phase sequence

B

Phasor magnitudes

C

Phase angles

Question 73 of 80

# Q.74 How many symmetrical components are generated from a single set of unbalanced phasors?

A

1

B

3

C

6

Question 74 of 80

# Q.75 What is the sequence of symmetrical components when the unbalanced phasors have ACB phase sequence?

A

Positive= ACB; Negative=ACB; Zero=none

B

Positive= ACB; Negative=ABC; Zero=none

C

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

A balanced set of phasors

B

The original unbalanced set of phasors

C

A different set of phasors

Question 76 of 80

# Q.77 How many symmetrical components are generated from a single set of balanced phasors?

A

1

B

3

C

6

Question 77 of 80

# Q.78 Why do we need ‘a’ operator?

A

To define all phasors in terms of one

B

It is present in the formula

C

No particular reason

Question 78 of 80

# Q.79 Is the ‘a’ operator sequence specific? (different for ABC and ACB phase sequence?)

A

Yes, in all cases

B

Yes, in some cases

C

No

Question 79 of 80

# Q.80 What is the benefit of using ‘a’ operator?

A

Decreases number of variables

B

Reduces equation complexity

C

Both

Question 80 of 80

# Q.81 How can we find symmetrical components from System phasors?

A

Iₛᵧₘₘₑₜᵣᵢ꜀ₐₗ = A * Iₛᵧₛₜₑₘ

B

Iₛᵧₘₘₑₜᵣᵢ꜀ₐₗ = A⁻¹ * Iₛᵧₛₜₑₘ

C

Iₛᵧₘₘₑₜᵣᵢ꜀ₐₗ = Iₛᵧₛₜₑₘ / A