The injection unit REX060 is connected to the generator and to IED as shown in figure 214.
7.13.8.3 General measurement of ground fault impedance
GUID-545BFD9B-BB9F-434C-AD03-B83F5DFC4811 v2
From the REX060 the injected voltage and current are delivered as AC voltages to IED. The injected
voltage and current is measured and analyzed in the protection function software within IED. The
measured injected voltage and current are first processed by means of special filtering so that the
signals are referred to the injected frequency only.
The bare complex impedance is, see fig 217:
EQUATION2500-ANSI V1 EN-US
An equivalent circuit for the measured impedance is shown in figure 217.
+
V
inj
-
I
inj
Z
shunt
R
f
Zseries
Z
bare
Z
Measured
ANSI11000003_1_en.vsd
ANSI11000003 V1 EN-US
Figure 217: Equivalent of the impedance measurement
In non-faulted operation R
f
is very large. A “healthy” impedance is calculated as:
1 2
Measured bare
Z k Z k= × +
EQUATION2501 V1 EN-US
The calculation of Z
measured
by Z
bare
,
k1
and
k2
is graphically shown in figure 218
The factors
k1
and
k2
[Ω] are derived during the calibration measurements under commissioning;
their values are calculated on the basis of measurements performed when known calibration
resistances are connected. The factor
k1
compensates for transformer ratio and other factors to
achieve impedance values related to the primary system. The factor
k2
[Ω] compensates for the
series impedance Z
series
The factors
k1
and
k2
are applied to the bare impedance Z
bare
, calculated from the measured
voltage and current, in order to convert it into the primary impedance Z
measured
. As support for the
calibration, the Injection Commissioning Tool must be used. This tool is an integrated part of the
PCM600 tool.
In connection to this calibration, the first reference impedance is also derived.
Section 7 1MRK 502 066-UUS B
Impedance protection
404
Technical manual
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