Zone 1 relays look at what percent of a line?

Zone 1 relays are designed to detect faults on transmission lines and typically cover a predetermined distance to ensure timely operation. Specifically, Zone 1 relays are set to operate for 90% of the line length. This setting helps to adequately clear faults close to the relay while minimizing the chance of unnecessary tripping for external faults. By monitoring up to 90% of the line, these relays can quickly react to incidents within their designated zone, ensuring the reliability of the transmission system.

The other percentages provided do not align with the conventional settings used for Zone 1 relays. For instance, covering more than 100% could risk tripping when the fault is outside the intended line, leading to a nuisance trip scenario. Therefore, the correct response accurately reflects the operational philosophy and reliability objectives of Zone 1 protection schemes.