The 2V73 relay provides high speed differential protection for various items of power system plant including generators, busbars, motors & the individual windings of power transformers. The 2V73 is also suitable for restricted earth fault applications. The relay measuring element is basically an attracted armature unit of simple & rugged construction powered from a bridge rectifier. Each phase of the relay can be set from 25 to 325V AC in 50V steps by using the front panel mounted selector switches. A capacitor is connected in series with the operating coil to make the relay insensitive to the DC component of fault current. The setting can thus be calculated in terms of RMS AC quantities without regard for the degree of offsets produced by the point on wave at which the fault occurs. An inductor connected in series with the capacitor forms a resonant circuit tuned to the relays rated frequency.