A primer on pilot protection with digital relays

The paper summarizes carrier aided distance protection schemes that have been used successfully for a very long time. Each scheme, their communication requirements have been discussed as well as their application conditions. It is noted that with the introduction of digital technology the capabilities of distance relays and their performance has been greatly improved and now we can access a lot of data from the relay concerning its decisions, measurements, local or remote inputs within a few milliseconds as well as data from other relays in the same substation and remote relays via digital communication techniques.