The MHOR04 is a well-established, high-speed protection relay for feeders. 

This high-speed protection for feeders is based on the Merz-Price circulating current system. It is suitable for the majority of plain feeders and provides a single-phase current for comparison over a pilot circuit. 

Merz-Price circulating system, single-phase current 
MHOR04 is based on the Merz-Price circulating current system. It is operational over privately owned two-core pilots with a relatively high core resistance (up to 1000O loop) level and a low intercore insulation level

MHOR04, which features a unit protection scheme with no time or current grading problems, even on ring circuits, can be used to protect the majority of plain feeders. The three line currents are united to provide a single-phase current for comparison over a pilot circuit.

High speed operations with superior through fault stability
MHOR04 operates at high speed, providing a through fault stability that is 50 times greater than the relay rating. With four output contacts, MHOR04 pilot circuits number up to 1000O 2.5µF.