Three-Phase Faults - ABB Relion 670 Series Technical Reference Manual

Section 6
Impedance protection
6.10.2.3
332
In the same way as the condition for phase-to-ground fault, there are current conditions
that have to be fulfilled in order to release the phase-to-phase loop. Those are
according to equation 30
<
3 0 I 3 0 I Enable PG _
EQUATION1814-ANSI V1 EN
<
3 0 I 3 0 I BLK _ PP
EQUATION1815-ANSI V1 EN
where:
3I0Enable_PG is the minimum operation current for forward ground measuring loops,
3I0BLK_PP
is 3I limit for blocking phase-to-phase measuring loop and
0
Iphmax is maximal magnitude of the phase currents.

Three-phase faults

The operation conditions for three-phase faults are the same as for phase-to-phase
fault, that is equation 29, equation
of the function.
However, the reach is expanded by a factor 2/√3 (approximately 1.1547) in all
directions. At the same time the characteristic is rotated 30 degrees, counter-clockwise.
The characteristic is shown in figure 104.
or equation 31.
30 and equation
1MRK505222-UUS C
31 are used to release the operation
Technical reference manual
(Equation 70)
(Equation 71)