The MFAC relay works as a high impedance unit protection device, with settings determined by a series of resistors. The resistors are chosen on a seven-way plug bridge. This supplied high-speed differential protection for distinct types of power system plants along with reactors, generators, busbars, motors and the unique windings of power transformers. Supplying high-speed differential protection, this is rapid and safe because of its simple electromechanical construction. MFAC34, contained of the three elements, supply both phase and earth fault protection. Wide settings range with a simple, robust design assuring high stability with through faults, its benefit from a simple application strategy.