The current measurement of the function is based on two alternative measurement
modes, "DFT" and "Peak-To-Peak". The measurement mode is selected using the
Measurement mode
setting.
If the current magnitude is below 0.02 · I
N
, where I
N
is the nominal phase current,
the impedance value is not evaluated and the maximum impedance value (99.999
pu) is shown in the Monitored data view.
The calculated impedances are converted to a pu impedance as the
operating characteristics are defined using the
Polar reach
setting in
%Zb.
The calculated phase-phase impedance amplitudes Z_AMPL_AB, Z_AMPL_BC and
Z_AMPL_CA are available as pu values in the Monitored data view.
Underimpedance detection
The operating characteristic is an origin-centric circle on the impedance plane. The
origin-centric circular characteristic is defined using the
Polar reach
setting. If the
calculated impedance value enters the circle in the impedance plane, the module
sends an enabling signal to start the Timer.
Figure 571: Origin-centric circular operating characteristics
Separate zones with an offset-mho characteristic can be designed using multiple
instances of the UZPDIS function with
Offset enable
setting and parameterized
with
Offset
and
Displacement
setting values as shown in Figure
Figure 572
.
Offset
is
the distance of the top of the circle from R-axis. If the sign of the
Offset
is positive,
the top of the circle is above the R-axis and if it is negative, the top of the circle
will be below the R-axis.
Displacement
is the distance by which the center of the
circle is displaced from the X-axis. If the sign of the
Displacement
setting is positive,
1MRS759142 F
Protection functions
REX640
Technical Manual
1029
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