Distance relays are generally

Distance relays are primarily used for the protection of transmission lines in power systems.

They operate based on the ratio of voltage to current (i.e., impedance) seen at the relay location. When a fault occurs, the impedance between the relay and the fault point drops. The relay measures this drop and operates if the impedance falls within a preset value.

Impedance relays are designed to detect this change in impedance and hence are best suited for distance protection.

Split-phase relays are used for other specialized protection schemes and are not suitable for distance protection.

Reactance relays are a type of distance relay, but they are more sensitive to resistive faults and are mainly used in specific conditions like high resistance ground faults. They are not as commonly used for general distance protection as impedance relays.

Therefore, impedance relays are the standard and most widely used type of distance relays.