The injection unit REX060 is connected to the generator and to IED as shown in figure
7.8.9.3
General measurement of earth fault impedance
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
Inj
Inj
bare
U
Z
I
=
EQUATION2500 V1 EN
An equivalent circuit for the measured impedance is shown in figure
+
U
inj
-
I
inj
Z
shunt
R
f
Z
series
IEC11000003-2-en.vsd
Z
Bare
Z
Measured
IEC11000003 V1 EN
Figure 128:
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
For definition of
k1
and
k2
The factors
k1
and
k2
[Ω] are derived from measurements during commissioning,
where calibration to known fault resistance will be used to convert the measurement
to true primary impedance. The factor
k1
will compensate for transformer ratio and
Section 7
1MRK502052-UEN B
Impedance protection
288
Technical manual
Summary of Contents for Relion REG670
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