What type of relays are typically found on both ends of a long transmission line?

What type of relays are typically found on both ends of a long transmission line?

• A. 11 Distance relays
• B. 21 Distance or 67 Directional Overcurrent relays
• C. 51 Overcurrent relays
• D. 27 Undervoltage relays

Answer: (B)

Distance relays are commonly used on both ends of a long transmission line to provide protection against faults. They measure the impedance of the line to determine the distance to a fault and can operate based on how far along the line a fault occurs. This functionality is crucial for long lines, as the distance to the fault can significantly influence the fault's characteristics and the protective action required. In addition to distance relays, 67 Directional Overcurrent relays are included in this choice because they provide an additional layer of protection by detecting overcurrent conditions in a specific direction. This capability is particularly important in transmission systems where current can flow from multiple sources, as it ensures that the relay will only operate for faults in the intended direction of power flow. Unlike the other options, which focus on different aspects of electrical protection (like overcurrent or undervoltage), the selected answer addresses the essential need for both distance measurement and directional protection in managing the specifics of faults on long transmission lines. This is critical for effective system operation and preventing widespread outages.

Distance relays are commonly used on both ends of a long transmission line to provide protection against faults. They measure the impedance of the line to determine the distance to a fault and can operate based on how far along the line a fault occurs. This functionality is crucial for long lines, as the distance to the fault can significantly influence the fault's characteristics and the protective action required.

In addition to distance relays, 67 Directional Overcurrent relays are included in this choice because they provide an additional layer of protection by detecting overcurrent conditions in a specific direction. This capability is particularly important in transmission systems where current can flow from multiple sources, as it ensures that the relay will only operate for faults in the intended direction of power flow.

Unlike the other options, which focus on different aspects of electrical protection (like overcurrent or undervoltage), the selected answer addresses the essential need for both distance measurement and directional protection in managing the specifics of faults on long transmission lines. This is critical for effective system operation and preventing widespread outages.