Relays And System Protection Quiz

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What do you understand by relays and system protection? Are you ready to take this relays and system protection quiz that we have designed? A protection relay is known as a smart device that is helpful in receiving inputs, comparing them to set points, and providing some outputs. These inputs can be current, voltage, resistance, or even temperature. So, let's see if you understand relays and system protection well enough or not.

• 1.

The number of pilot wires required for protecting 3-phase transmission lines using the Translay method of protection is:

• A.

6

• B.

4

• C.

3

• D.

2

D. 2
Explanation
The Translay method of protection for 3-phase transmission lines requires 2 pilot wires. This method uses a differential relay scheme where the currents in the pilot wires are compared to detect any fault in the transmission line. By comparing the currents, the relay can determine if there is a fault and initiate the necessary protection actions. Therefore, only 2 pilot wires are needed for this method of protection.

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• 2.

A Mho relay is a:

• A.

Voltage restrained directional relay

• B.

Voltage controlled over current relay

• C.

Directional restrained over current relay

• D.

Directional restrained over voltage relay

A. Voltage restrained directional relay
Explanation
A Mho relay is a voltage restrained directional relay. This means that it operates based on the voltage across the relay terminals and is restrained by the voltage level. It also has directional capabilities, meaning it can detect the direction of the fault current flow. This type of relay is commonly used in power systems to protect transmission lines and generators, as it can accurately detect faults and provide directional information for quick and effective fault clearing.

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• 3.

If the time operation of a relay for unity TMS is 10 sec, what is the time of operation for 0.5 TMS:

• A.

20

• B.

5

• C.

10

• D.

None

B. 5
Explanation
The time of operation for 0.5 TMS would be half of the time of operation for unity TMS. Since the time of operation for unity TMS is 10 seconds, the time of operation for 0.5 TMS would be 5 seconds.

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• 4.

The Buckholtz relay protects  a transformer from:

• A.

All types of internal faults

• B.

A turn to turn fault

• C.

Winding to Winding Fault

• D.

None

A. All types of internal faults
Explanation
The Buckholtz relay is a protective device used to safeguard transformers from various internal faults. It is designed to detect faults such as turn-to-turn faults, winding-to-winding faults, and other types of internal faults. By monitoring the flow of current and voltage within the transformer, the Buckholtz relay can quickly identify any abnormal conditions and initiate the necessary protective actions to prevent further damage to the transformer. Therefore, the Buckholtz relay provides protection against all types of internal faults in a transformer.

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• 5.

The purpose of a differential relay on a transformer is to

• A.

Protect against external faults

• B.

Protect against internal faults

• C.

Protect against overvoltage

• D.

Protect against under current

B. Protect against internal faults
Explanation
A differential relay on a transformer is designed to protect against internal faults. This means that it monitors the current flowing into and out of the transformer and compares the two values. If there is a significant difference between the incoming and outgoing current, it indicates a fault within the transformer. The differential relay then operates to isolate the faulty section and prevent further damage to the transformer. This type of protection is crucial in ensuring the safe and efficient operation of the transformer.

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• 6.

B.
• 7.

A type of relay in which the time of relaying varies directly as the distance of the fault from the station

• A.

Distance Relay

• B.

Differential Relay

• C.

Overcurrent

• D.

Pilot

A. Distance Relay
Explanation
A distance relay is a type of relay that operates based on the distance of the fault from the station. The time it takes for the relay to activate is directly proportional to the distance of the fault. This means that the farther the fault is from the station, the longer it takes for the relay to respond. Distance relays are commonly used in power systems to protect transmission lines and detect faults. They provide accurate and reliable protection by considering the distance of the fault, allowing for timely and appropriate actions to be taken to prevent damage to the system.

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• 8.

Which of the following types of relays are used to protect transformers and generators?

• A.

Directional overcurrent Relays

• B.

Differential Relay

• C.

Thermal Relays

• D.

Single Pole Relays

B. Differential Relay
Explanation
Differential relays are used to protect transformers and generators because they compare the current entering and leaving the equipment. If there is a difference in the current, it indicates a fault or an abnormal condition, and the relay will trip to isolate the equipment from the fault. This helps to prevent damage to the transformers and generators and ensures their safe operation.

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• 9.

What is not a protected equipment in a substation?

• A.

Shunt Equipment Protection

• B.

Bus Protection

• C.

Transformer Protection

• D.

Circuit Breaker Failure Protection

• E.

Under frequency Load Shedding

• F.

Variable condeser

F. Variable condeser
Explanation
A variable condenser is not a protected equipment in a substation. The other options listed - Shunt Equipment Protection, Bus Protection, Transformer Protection, Circuit Breaker Failure Protection, and Under frequency Load Shedding - are all examples of protective measures or equipment used in a substation to ensure the safe and efficient operation of the electrical system. However, a variable condenser is not typically used for protection purposes in a substation.

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• 10.

A type of relaying which is responsive to the direction of the flow of power and line impedance is normally designed as

• A.

Distance relaying

• B.

Pilot protection

• C.

Power relaying

• D.

Differential relaying/protection

A. Distance relaying
Explanation
Distance relaying is a type of protective relaying that is designed to respond to the direction of power flow and line impedance. It measures the impedance of the transmission line and compares it to a pre-set distance characteristic. If the impedance exceeds the set value, it indicates a fault and the relay operates to isolate the faulty section. This type of relaying is commonly used in power systems to protect transmission lines from faults and ensure reliable power delivery.

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• 11.

Reactance relay is normally preferred for protection against:

• A.

Earth faults only

• B.

Phase Faults only

• C.

3 phase to ground faults

• D.

Single phase ground faults

A. Earth faults only
Explanation
Reactance relay is normally preferred for protection against earth faults only. This is because reactance relays are designed to detect faults that occur between a phase conductor and the earth. These relays measure the reactance of the system and can quickly detect any changes in this reactance caused by an earth fault. They are not designed to detect phase faults, 3 phase to ground faults, or single phase ground faults. Therefore, reactance relays are specifically used for protection against earth faults only.

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• 12.

An overhead line with series compensation is protected using:

• A.

Impedance Relay

• B.

Reactance relay

• C.

Mho relay

• D.

None of the above

D. None of the above
• 13.

Distance Relays may be directional or non-directional

• A.

True

• B.

False

A. True
Explanation
Distance relays are protective devices used in power systems to detect and respond to faults or abnormal conditions. They are designed to measure the impedance or distance between the relay location and the fault point. Directional distance relays are capable of determining the direction of the fault based on the phase angle of the measured impedance. On the other hand, non-directional distance relays do not consider the fault direction and only rely on the magnitude of the impedance. Therefore, it is true that distance relays may be either directional or non-directional depending on their design and application.

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• 14.

This value is the determinant as to how long a short circuit will remain on a circuit, if uninterrupted by an overcurrent protective device.

• A.

Time of fault

• B.

At what point did the fault occur

• C.

X/R

• D.

Single or 3 phase

C. X/R
Explanation
The X/R ratio is the correct answer because it determines how long a short circuit will last on a circuit if there is no overcurrent protective device to interrupt it. The X/R ratio is a measure of the reactance (X) to resistance (R) in the circuit, and a higher X/R ratio indicates a longer duration of the short circuit.

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• 15.

Used to provide high speed tripping for end zone faults (beyond Zone 1's reach).

• A.

Directional Over Current

• B.

Distance Relay

• C.

Pilot Schemes

• D.

Out-of-Step Relaying

C. Pilot Schemes
Explanation
Pilot schemes are used to provide high speed tripping for end zone faults that are beyond Zone 1's reach. These schemes involve the use of communication channels to exchange information between relays located in different zones. By coordinating the operation of these relays, pilot schemes ensure that faults outside of Zone 1 are detected and cleared quickly, improving the overall reliability and efficiency of the protection system.

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• 16.

In the short circuit analysis, the rate of decay of fault current depends on:

• A.

L/R ratio

• B.

Single or 3 phase

• C.

At what point did the fault occur

• D.

Time of fault relative to the volatge

A. L/R ratio
Explanation
The rate of decay of fault current in short circuit analysis depends on the L/R ratio. The L/R ratio represents the ratio of inductance (L) to resistance (R) in the circuit. A higher L/R ratio indicates a higher inductance relative to resistance, which results in a slower decay of fault current. Conversely, a lower L/R ratio indicates a lower inductance relative to resistance, leading to a faster decay of fault current. Therefore, the L/R ratio is a crucial factor in determining the rate of decay of fault current in short circuit analysis.

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• 17.

Used to provide communication channel between the line sections of a terminal to determine if fault is internal or external

• A.

Directional Over Current

• B.

Distance Relay

• C.

Pilot Schemes

• D.

Out-of-Step Relaying

C. Pilot Schemes
Explanation
Pilot schemes are used to provide a communication channel between the line sections of a terminal to determine if a fault is internal or external. This means that pilot schemes enable the detection and localization of faults in a power system by exchanging information between different sections of the system. By analyzing the data received from the pilot schemes, it is possible to identify whether the fault is occurring within the system or if it is external, helping to improve the reliability and efficiency of the power transmission network.

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• 18.

If the fault current is 2000 amps, the relay setting is 50% and the C.T. is 400/5, then the plug setting multiplier should be:

• A.

25 amps

• B.

15 amps

• C.

50 amps

• D.

None of the above

D. None of the above
Explanation
The plug setting multiplier is calculated by dividing the relay setting by the product of the fault current and the current transformer ratio. In this case, the fault current is 2000 amps and the C.T. ratio is 400/5. Therefore, the product of the fault current and the C.T. ratio is 2000 * (400/5) = 160,000. Since the relay setting is 50%, the plug setting multiplier should be 0.5 / 160,000 = 0.000003125. None of the given options (25 amps, 15 amps, 50 amps) match this value, so the correct answer is "None of the above".

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• 19.

In this protection scheme the relay at one end detects a fault, it is turned on to signal the other end of the line that a fault has occurred.

• A.

Transfer Tripping

• B.

Directional Comparison

• C.

Phase Comparison

• D.

Pilot-Wire

A. Transfer Tripping
Explanation
Transfer tripping is a protection scheme where a relay at one end of a line detects a fault and sends a signal to the other end of the line to trip the circuit. This scheme ensures that the faulted section of the line is isolated quickly and efficiently, preventing further damage to the system. By transferring the tripping signal from one end to the other, the scheme allows for fast fault detection and isolation, improving the overall reliability and safety of the power system.

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• 20.

Faults within the protection zone are called?

• A.

Internal faults

• B.

External faults

• C.

Line Faults

• D.

Bus Faults

A. Internal faults
Explanation
Internal faults refer to faults that occur within the protection zone, which is the area covered by the protective devices. These faults can occur within the electrical equipment, such as transformers, generators, or transmission lines. When an internal fault occurs, the protective devices are designed to detect and isolate the fault, preventing further damage to the equipment and ensuring the safety of the system.

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• 21.

Magnitude of the short circuit depends least based on what?

• A.

Circuit reactance

• B.

Capacity of the generator

• C.

Synchronous Reactance

• D.

Circuit Resistor

C. Synchronous Reactance
Explanation
The magnitude of the short circuit depends least on the synchronous reactance. Short circuit refers to a low-resistance connection between two points in an electric circuit. The synchronous reactance is the imaginary component of the synchronous impedance, which represents the opposition to the flow of current due to the magnetic field in a synchronous machine. However, the magnitude of the short circuit is primarily influenced by the circuit reactance, circuit resistor, and capacity of the generator.

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• 22.

Faults outside the protection zone are called?

• A.

Internal faults

• B.

External faults

• C.

Line Faults

• D.

Bus Faults

B. External faults
Explanation
External faults are faults that occur outside the protection zone. These faults can be caused by factors such as lightning strikes, vegetation contact, or equipment failure in the transmission or distribution system. When these faults occur, the protection system is designed to detect and isolate them to prevent further damage to the system. Therefore, external faults are the correct answer to this question.

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• 23.

In this protection scheme over-current fault detecting relays are used to compare the relative phase angles of the currents at the to terminals.

• A.

Transfer Tripping

• B.

Directional Comparison

• C.

Phase Comparison

• D.

Pilot-Wire

C. Phase Comparison
Explanation
In this protection scheme, over-current fault detecting relays are used to compare the relative phase angles of the currents at the two terminals. This means that the protection system is designed to detect faults by comparing the phase angles of the currents. By comparing the phase angles, the system can determine if there is a fault and take appropriate action to protect the system. This method is known as phase comparison and is commonly used in protection schemes to detect faults and prevent damage to the electrical system.

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• 24.

What is not a possible zone of protection in a power system?

• A.

Bus Bars

• B.

Lines

• C.

Capacitor or reactor banks

• D.

Utilization equipment

• E.

High pass filters

• F.

Generators

• G.

Transformers

E. High pass filters
Explanation
High pass filters are not a possible zone of protection in a power system. In a power system, zones of protection are designed to detect and isolate faults or abnormal conditions to prevent damage to equipment and ensure the safety and reliability of the system. Bus bars, lines, capacitor or reactor banks, utilization equipment, generators, and transformers are all components that can be protected within the power system. However, high pass filters are not typically used as a zone of protection in power systems.

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• 25.

In this protection scheme the magnitude and phase angle of the current flowing at each end of the line determine whether an internal fault exists.

• A.

Transfer Tripping

• B.

Directional Comparison

• C.

Phase Comparison

• D.

Pilot-Wire

D. Pilot-Wire
Explanation
In a pilot-wire protection scheme, the magnitude and phase angle of the current flowing at each end of the line are used to determine if there is an internal fault. This means that the pilot-wire protection system relies on comparing the current measurements at both ends of the line to identify any discrepancies in magnitude or phase angle, which would indicate the presence of a fault. Therefore, the correct answer is Pilot-Wire.

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• 26.

How many protection zones are possible in a power system?

• A.

7

• B.

6

• C.

5

• D.

4

B. 6
Explanation
In a power system, protection zones are created to ensure the safety and reliability of the system. These zones are established to isolate faults and protect equipment. The number of protection zones depends on the complexity and size of the power system. It is possible to have six protection zones in a power system, each serving a specific area or equipment. These zones help in detecting and responding to faults, minimizing damage and ensuring the smooth operation of the system.

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• 27.

Which of the following is the most severe fault?

• A.

Three phase fault

• B.

Single line to ground

• C.

Double line to ground fault

• D.

Earth ground interrupt

A. Three phase fault
Explanation
A three phase fault is the most severe fault among the given options. This type of fault occurs when all three phases of a power system come into contact with each other or with the ground. It results in a large amount of current flowing through the system, causing significant damage to equipment and potentially leading to power outages. Compared to single line to ground and double line to ground faults, a three phase fault involves a higher magnitude of fault current and poses a greater risk to the stability and reliability of the power system.

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• 28.

What component is not normally used in the protection of a power system?

• A.

Current Transformers (CTs)

• B.

Variable Reactors

• C.

Voltage Transformers (PTs)

• D.

Coupling Capacitance Volatge Transformers (CCVTs)

B. Variable Reactors
Explanation
Variable reactors are not normally used in the protection of a power system. Variable reactors are primarily used for controlling the flow of reactive power in a power system, rather than for protection purposes. In contrast, current transformers (CTs), voltage transformers (PTs), and coupling capacitance voltage transformers (CCVTs) are commonly used in power system protection. CTs are used to measure and monitor the current flowing through power system components, PTs are used to measure and monitor the voltage levels, and CCVTs are used for voltage measurement and protection in high voltage systems.

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• 29.

C.
• 30.

In adjacent overlapping zones in the DWP 500-kv systems, what component or device is normally overlapped?

• A.

Relay

• B.

Transformer

• C.

Disconnect

• D.

Circuit Breaker

D. Circuit Breaker
Explanation
In adjacent overlapping zones in the DWP 500-kv systems, circuit breakers are normally overlapped. Circuit breakers are essential devices that protect electrical systems from damage caused by excessive current. In overlapping zones, multiple circuit breakers are installed to ensure that if one circuit breaker fails, the adjacent one can provide backup protection. This overlapping arrangement helps to maintain the reliability and stability of the electrical system by minimizing the risk of power outages and equipment damage.

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• 31.

D.
• 32.

The ratio of reset to pickup for an induction cup relay is approx:

• A.

0.99

• B.

1.01

• C.

0.75

• D.

None

A. 0.99
Explanation
The ratio of reset to pickup for an induction cup relay is approximately 0.99. This means that the relay will reset at a slightly lower value than the pickup value. In other words, the relay will activate or pick up at a certain threshold, and it will reset or deactivate at a slightly lower threshold. This ratio allows for a small hysteresis or difference between the activation and deactivation points, which can help to prevent rapid cycling or chattering of the relay in response to small fluctuations in the input signal.

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• 33.

E.
• 34.

In this protection scheme the relays at each line terminal determine the direction of the fault current and compare their individual results over the pilot or communication channel.

• A.

Transfer Tripping

• B.

Directional Comparison

• C.

Phase Comparison

• D.

Pilot-Wire

B. Directional Comparison
Explanation
Directional comparison is a protection scheme where the relays at each line terminal analyze the direction of the fault current and compare their individual results over the pilot or communication channel. This scheme is used to determine the direction of the fault and selectively trip the appropriate circuit breakers to isolate the faulted section of the power system. By comparing the directional information from multiple relays, this scheme allows for reliable fault detection and selective tripping, minimizing the impact on the rest of the power system.

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• 35.

F.
• 36.

Mho relay is normally used for the protection of:

• A.

Long transmission lines

• B.

Medium length lines

• C.

Short length lines

• D.

No length criterion

A. Long transmission lines
Explanation
Mho relay is normally used for the protection of long transmission lines. This is because long transmission lines are more susceptible to faults and require more precise and sensitive protection mechanisms. Mho relays are distance relays that operate based on the impedance measured at a specific distance from the relay location. They are able to accurately detect faults and provide reliable protection for long transmission lines.

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• 37.

For protection of parallel feeders fed from one end the relays required are:

• A.

Non-directional relays at the source end and directional relays at the load end

• B.

Non-directional relays at both ends

• C.

Directional relays at the source and non-directional relays at the load end

• D.

Directional relays at both ends

A. Non-directional relays at the source end and directional relays at the load end
Explanation
For the protection of parallel feeders fed from one end, it is necessary to have non-directional relays at the source end and directional relays at the load end. Non-directional relays at the source end are used to detect any faults occurring on the parallel feeders, regardless of the direction of the fault current. On the other hand, directional relays at the load end are used to detect faults occurring on the parallel feeders in the direction away from the source. This combination ensures that faults at both ends of the parallel feeders can be detected and isolated effectively.

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• 38.

If the phase angle of the voltage col of a directional relay is 50' the maximum torque angle of the relay is:

• A.

130

• B.

100

• C.

25

• D.

None of the above

D. None of the above

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• Current Version
• Sep 02, 2023
Quiz Edited by
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• Sep 11, 2013
Quiz Created by
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