What is the term for relaying that depends on communication between line terminals?

The term that describes relaying which relies on communication between line terminals is piloting relay. This type of relay utilizes external communication systems to provide information about the conditions at different locations along a transmission line. By exchanging data between the terminals, the piloting relay can make more informed decisions about protection and control, enhancing the overall reliability and stability of the electrical grid.

In contrast, block relays are designed to prevent the operation of other relays in certain conditions and typically do not rely on inter-terminal communication. Electrical relays generally operate based on electrical quantities without the need for such communication. Main relays are usually responsible for primary protection functions but again do not typically use inter-terminal communication in the same manner as piloting relays. This distinction highlights the unique role that piloting relays play in the protection of transmission lines through their communicative capabilities.