1.
The injection is made to the faultless generator and the measured complex impedance is
stored.
2.
A known resistance is connected between the generator neutral point (see Figure
) and
earth.
The injection is made to the generator and the measured complex impedance is stored.
3.
The generator neutral point (see Figure
) is directly short-circuited to the earth. The
injection is made to the generator and the measured complex impedance is stored.
The sequence of the calibration steps is driven by ICT and it is shown in the figure below. The
connection of the calibration resistance and short circuit is shown here for the case with
injection in the generator neutral point through the neutral point VT and generator grounding
through primary resistor.
+
U
inj
-
R
N
C
stat
+
U
inj
-
R
N
C
stat
+
U
inj
-
R
N
C
stat
R
test
Step 1
Step 2
Step 3
I
inj
I
inj
I
inj
a
b
a
b
a
b
IEC11000044-1-en.vsd
GUID-9E470F57-D670-430C-BD27-CBF11AF92D1E V1 EN-US
Figure 19: Different steps at calibration measurements
There are other generator grounding methods and injection alternatives; the injection can be
performed through:
•
LV winding of a distribution transformer (DT) located at the stator neutral point
•
Open delta winding of a three-phase VT set located at generator terminals
•
Open delta winding of a three-phase grounding transformer (GT) located at generator
terminals
Whatever injection alternative is used, the neutral point of the generator must be accessible in
order to connect the calibration resistance (step 2) and short circuit (step 3) during the
calibration.
Commissioning
The generator can be in several operating conditions, for example:
•
Generator stand still
•
Generator running up, not synchronized to the network (circuit breaker open)
•
Generator normal operation (circuit breaker closed)
Other operating conditions can be identified.
Different operating conditions of the machine may require different reference impedances.
Section 7
1MRK 502 067-UEN B
Calibrating injection based 100% stator earth fault protection
64
Commissioning manual
