ImpedanceAngXRZ1FwdZ1RevIEC10000176-2-en.vsdIEC10000176 V2 ENFigure 57: Mho, offset mho characteristic for Zone 1 with setting parametersZ1Fwd, Z1Rev and ImpedanceAngThe three impedance zones can be time delayed individually by setting the parametertZx (where x is 1-3 depending on selected zone). For instantaneous operation set theparameter tZx to 0.00 s for the particular zone. To enable the zone, the operation modefor the zone, OpModeZx (where x is 1-3 depending on selected zone), has to be set toOn.The function are blocked in the following ways:• Activating of input BLOCK blocks the whole function.• Activating of the input BLKZ (fuse failure) blocks all output signals.The activation of input signal BLKZ can be made by external or internal fuse failurefunction.7.2.6.4 Theory of operationThe mho algorithm is based on the phase comparison of a operating phasor and apolarizing phasor. When the operating phasor leads the polarizing phasor by morethan 90 degrees, the function operates and gives a trip output.1MRK 504 135-UEN A Section 7Impedance protection135Technical manual
