ABB Relion 670 series, Техническое руководство

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7.8.7.4 Directional element
GUID-24431EEC-5037-41CD-BC4A-7AC196F158F3 v4
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.
15°< 120°
I
arg
PolA
A
V
- <
ANSIEQUATION15059 V1 EN-US
(Equation 82)
V
15°< 120°
I
arg
PolAB
AB
- <
ANSIEQUATION15060 V1 EN-US
(Equation 83)
Where:
V
PolA
is the polarizing voltage for phase A.
I
A
is the phase current in phase A.
V
PolAB
is the polarizing voltage difference between phase A and B (B lagging A).
I
AB
is the current difference between phase A and B (B lagging A).
The corresponding reverse directional sectors range from 165 to -60 degrees.
Since the polarizing voltage is also used for the Mho distance characteristics, the magnitude of
the voltage is just as interesting as the phase. If there are symmetrical conditions and the
measured per phase positive sequence voltage magnitude is above 75% of the base voltage
before the fault, the pre-fault magnitude will be memorized and used as long as there is a fault.
The phase angle however will only be memorized (locked) for 75 ms at a time, not to lose
synchronism with the real system voltage.
Should the positive sequence voltage drop below 2% of the base voltage, it will be considered
invalid. In this situation, directional signals and pickups from Mho elements will be sealed-in and
kept static as long as there is a fault.
For ZMFCPDIS, when option SeriesComp is chosen for OperationSC, the voltages of faulty phases
will be discarded in order not to affect the polarizing voltage with voltage reversal.
7.8.7.5 Fuse failure
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The ZMFPDIS function has to be blocked by an additional function like the Fuse failure supervision
(FUFSPVC) or an equivalent external device. Typically, the binary input VTSZ is used for this
purpose.
1MRK 502 066-UUS B Section 7
Impedance protection
305
Technical manual