particular installation alarm sensitivity of up to 50 kΩ may be reached at steady state operating
condition of the machine.
Note that it is possible to connect two REG670 in parallel to the REX060 injection unit in order to
obtain redundant measurement in two separate IEDs. However, at commissioning both REG670
IEDs must be connected during calibration procedure.
7.14.8.4 General measurement of ground fault impedance
GUID-8447C1E8-575F-481C-81FF-28B120F13DA7 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
229:
EQUATION2500 V1 EN-US
An equivalent circuit for the measured impedance is shown in figure 225.
+
U
inj
-
I
inj
Z
shunt
R
f
Zseries
IEC11000003-2-en.vsd
Z
Bare
Z
Measured
IEC11000003 V1 EN-US
Figure 229: 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 232.
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 other factors to achieve
impedance values related to the primary system. The factor
k2
[Ω] will compensate for the series
impedance Z
series
.
Section 7 1MRK 502 066-UUS B
Impedance protection
426
Technical manual
To Next Page
Loading...
