ABB REG670 - Page 191

where
U L1L2
EQUATION1790 V2
EN
is the voltage vector difference between phases L1 and L2
I L1L2
EQUATION1791 V2
EN
is the current vector difference between phases L1 and L2
ZPP is the positive sequence impedance setting for phase-to-phase fault
U
pol
is the polarizing voltage
The polarized voltage consists of 100% memorized positive sequence voltage
(UL1L2 for phase L1 to L2 fault). The memorized voltage will prevent collapse of the
Mho circle for close in faults.
Operation occurs if 90≤β≤270
ZPPI 2L1L •
L1L2
comp U=U
ß
IL1L2·X
IL1L2·R
-
ZPPI
2L1L
•
2L1LU
polU
en07000109.vsd
IEC07000109 V1 EN
Figure 66: Simplified mho characteristic and vector diagram for phase L1-to-L2
fault
Offset Mho
The characteristic for offset mho is a circle where two points on the circle are the
setting parameters ZPP and ZRevPP. The vector ZPP in the impedance plane has the
settable angle AngZPP and the angle for ZRevPP is AngZPP+180°.
1MRK502052-UEN B Section 7
Impedance protection
185
Technical manual