ABB Modures LZ92-1 - Page 16

Reverse reach
The effective forwards (XA) and reverse (XB) reaches can be entered in the
diagram of Fig. 3. 2. The ratio XB/XA is set on PCB 3 by inserting the
appropriate value for resistor Wi4 from 0.26 to 3.91 (Z./0.26/ to /Z.3.91/
in the ordering code, see Fig. 9.26).
Extreme forwards reaches
Values of XB/X greater than 1 are of consequence when an extreme forwards
reach is needefr. This is achieved by reversing the primary current connec-
tions to the distance relay and then reversing the measuring direction of
the distance unit (using switch Sb on PCB 8, order number HESG 439 686,
respectively switch I~ on the front of PCB 8, HESG 440 718). The forwards
reach then corresponds to the frontplate setting multiplied by the set
ratio XB/XA.
The pick-up criterion in the diagram of Fig. 3.2 is no longer determined by
U,1 ..L u;, but instead by <f (~, lJi) = 108°. The change is made with the aid
of the soldered link LB3 on PCB 3 (see Fig. 9.26).
The reach for earth faults corresponds to the frontplate setting providing
the k factor for the starting units matches that of the line (k = k L).
The s<Earter k is set using resistor Wi5 on PCB 2 in KZ91 or K~~l-1 ~see
0
Fig. 9.25).
The above changes may be used singly or in conjunction with each other!
3.3 k factor for the distance measuring system
-0
14
The compensation of the zero-sequence impedance is calculated from the positive-
sequence impedance ZL and zero-sequence impedance Z of the line or cable.
oL
1
3
This zero-sequence compensation factor k is set on the front of the EW91
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(according to HESG 438 454) as follows:
EW91 code K.0: Only the magnitude of (lk I> is set.
This is generally all t.ha~ is necessary in the case of overhead
lines (thumbwheel switch 'Pk set to zero).
0
EW91 code K.1: Both the magnitude Clk I) and phase-angle ('Pk ) are set, which
is of consequence abov~ all in cable systems.
0