Theory Of Operation - ABB RET650 Technical Manual

1MRK 504 135-UEN A
7.2.6.4
Technical manual
IEC10000176 V2 EN
Figure 57: Mho, offset mho characteristic for Zone 1 with setting parameters
Z1Fwd, Z1Rev and ImpedanceAng
The three impedance zones can be time delayed individually by setting the parameter
tZx (where x is 1-3 depending on selected zone). For instantaneous operation set the
parameter tZx to 0.00 s for the particular zone. To enable the zone, the operation mode
for the zone, OpModeZx (where x is 1-3 depending on selected zone), has to be set to
On.
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 failure
function.

Theory of operation

The mho algorithm is based on the phase comparison of a operating phasor and a
polarizing phasor. When the operating phasor leads the polarizing phasor by more
than 90 degrees, the function operates and gives a trip output.
Impedance protection
X
ImpedanceAng
IEC10000176-2-en.vsd
Section 7
R
135