ABB Relion 650 Series Technical Manual page 115

1MRK 506 326-UUS B
The activation of input signal BLKZ can be made by external fuse failure function or from the loss
of voltage check in the Mho supervision logic (ZSMGAPC). In both cases the output BLKZ in the
Mho supervision logic shall be connected to the input BLKZ in the Mho distance function block
(ZMOPDIS, 21)
5.3.6.4 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.
Phase-to-phase fault
Mho
The plain mho circle has the characteristic as in figure 58. The condition for deriving the angle β is
according to equation 13.
(
β =
arg
EQUATION1789-ANSI-650 V1 EN-US
where
V
AB
V1 EN-US EQUATION1790-ANSI
I
AB
EQUATION1791-ANSI V1 EN-US
Z
V
pol
The polarized voltage consists of 100% memorized positive sequence voltage (VAB for phase A to
B fault). The memorized voltage will prevent collapse of the mho circle for close in faults.
Operation occurs if 90≤β≤270
Line distance protection REL650
Technical manual
( )
)
V I Z V
− ⋅ −
arg
AB AB pol
is the voltage vector difference between phases A and B
is the current vector difference between phases A and B
is the positive sequence impedance setting for fault
is the polarizing voltage
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Section 5
Impedance protection
SEMOD154224-46 v3
SEMOD154224-240 v2
SEMOD154224-217 v4
(Equation 13)
109