ABB Relion 670 series, Technical Reference Manual

Page: 338 / 1232

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 or equation 31 .
3 0 3 0 _ I I Enable PG
<
EQUATION1814-ANSI V1 EN
(Equation 70)
3 0 3 0 _ I I BLK PP
<
EQUATION1815-ANSI V1 EN
(Equation 71)
where:
3I0Enable_PG is the minimum operation current for forward ground measuring loops,
3I0BLK_PP
is 3I
0
limit for blocking phase-to-phase measuring loop and
Iphmax is maximal magnitude of the phase currents.
6.10.2.3 Three-phase faults
The operation conditions for three-phase faults are the same as for phase-to-phase
fault, that is equation
29 , equation 30 and equation 31 are used to release the operation
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 .
Section 6
1MRK505222-UUS C
Impedance protection
332
Technical reference manual