IA Phase current in phase A
V1AB Voltage difference between phase A and B (B lagging A)
V1ABM Memorized voltage difference between phase A and B (B lagging A)
IAB Current difference between phase A and B (B lagging A)
The default settings for
AngDir
and
AngNegRes
are 15 (= -15) and 115 degrees respectively (see
figure 112) and they should not be changed unless system studies show the necessity.
If one sets
DirEvalType
to
Comparator
(which is recommended when using the mho characteristic)
then the directional lines are computed by means of a comparator-type calculation, meaning that
the directional lines are based on mho-circles (of infinite radius). The default setting value
Impedance
otherwise means that the directional lines are implemented based on an impedance
calculation equivalent to the one used for the quadrilateral impedance characteristics.
When
Directional impedance element for mho characteristic
(ZDMRDIR) is used
together with
Fullscheme distance protection, mho characteristic
(ZMHPDIS) the
following settings for parameter
DirEvalType
is vital:
• alternative
Comparator
is strongly recommended
• alternative
Imp/Comp
should generally not be used
• alternative
Impedance
should not be used. This altenative is intended for use
together with Distance protection zone, quadrilateral characteristic
(ZMQPDIS)
X
R
-AngDir
AngNegRes
Zset reach point
-Zs
en06000416_ansi.vsd
ANSI06000416 V1 EN-US
Figure 112: Setting angles for discrimination of forward fault
The reverse directional characteristic is equal to the forward characteristic rotated by 180
degrees.
The code built up for release of the measuring fault loops is as follows: STDIRCND = AN*1 + BN*2 +
CN*4 + AB*8 + BC*16 + CA*32
Example: If only ANpickup, the value is 1, if pickup in AN and CN are detected, the value is 1+4=5.
1MRK 502 066-UUS B Section 7
Impedance protection
239
Technical manual
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