ABB RELION 670 Series Technical Manual page 349

1MRK 502 066-UUS B
Phase-to-phase-ground faults (also called double ground faults) will practically always activate
phase-to-phase zone measurements. This is a substantial difference compared to the previous
phase selection function in the 500- and 600-series (that is, FDPSPDIS). Measurement in two
phase-to-ground loops at the same time is associated with so-called simultaneous faults: two
ground faults at the same time, one each on the two circuits of a double line, or when the zero
sequence current is relatively high due to a source with low Z0/Z1 ratio.In fact, in these situations
zone measurement will be released both for the related phase-to-ground loops and the phase-to-
phase loop simultaneously. On the other hand, simultaneous faults closer to the remote bus will
gradually take on the properties of a phase-to-phase-ground fault and the function will eventually
use phase-to-phase zone measurements also here.
In cases where the fault current infeed is more or less completely lack of zero sequence nature (all
phase currents in phase), the measurement will be performed in the phase-to-ground loops only
for a phase-to-phase-ground fault.
However, should it be desirable to use phase-to-ground (and only phase-to-ground) zone
measurement for phase-to-phase-ground faults, the setting
excessive default value to the level above which phase-to-ground measurement should be
activated.
7.9.7.4 Directional element
Several criteria are employed when making the directional decision. The basis is provided by
comparing a positive sequence based polarizing voltage with phase currents. For extra security,
especially in making a very fast decision, this method is complemented with an equivalent
comparison where, instead of the phase current, the change in phase current is used. Moreover, a
basic negative sequence directional evaluation is taken into account as a reliable reference during
high load condition. Finally, zero sequence directional evaluation is used whenever there is more or
less exclusive zero sequence in-feed.
Fundamentally, the directional sectors that represent forward direction, one per measuring loop,
are defined by the following equations.
V
PolA
arg
-
15°<
I
ANSIEQUATION15059 V1 EN-US
V
PolAB
arg
-
15°<
I
ANSIEQUATION15060 V1 EN-US
Where:
V
PolA
I
A
V
PolAB
I
AB
The corresponding reverse directional sectors range from 165 to -60 degrees.
Technical manual
<
120°
A
<
120°
AB
is the polarizing voltage for phase A.
is the phase current in phase A.
is the polarizing voltage difference between phase A and B (B lagging A).
is the current difference between phase A and B (B lagging A).
Impedance protection
INReleasePE can be lowered from its
GUID-24431EEC-5037-41CD-BC4A-7AC196F158F3 v4
Section 7
(Equation 95)
(Equation 96)
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