During the three steps described above a check is made that there are sufficient changes in
the measured impedance in order to guarantee that there is no primary fault from the
beginning or other problems due to the installation or calibration procedure.
The sequence of the calibration session follows a scheme shown in the tool.
•
Calibration sequence 1: The injection must be activated and the rotor must be left with no
impedance connected. The ICT now makes consecutive measurements until the statistical
error reaches an acceptable value. This is graphically shown in a diagram. The user stops
the sequence by acceptance of the measurement. The result is stored for later
calculations.
•
Calibration sequence 2: A known resistor is connected between the rotor winding and
earth. The value of the resistance is the input to ICT. The ICT now makes consecutive
measurements until the statistical error reaches an acceptable value. This is graphically
shown in a diagram. The user stops the sequence by acceptance of the measurement. The
result is stored for later calculations.
•
Calibration sequence 3: The generator rotor winding is now directly connected to earth.
The ICT now makes consecutive measurements until the statistical error reaches an
acceptable value. This is graphically shown in a diagram. The user stops the sequence by
acceptance of the measurement. The result is stored for later calculations.
The sequence of the calibration steps is driven by ICT and it is shown in the figure below.
DC
AC
C
rot
REX
061
I
inj
DC
AC
C
rot
REX
061
I
inj
DC
AC
C
rot
REX
061
I
inj
R
Test
IEC11000205-1-en.vsd
Step 1
Step 2
Step 3
IEC11000205 V1 EN-US
Figure 9:
Different steps at calibration measurements
After the three steps ICT calculates the complex factors
k1 and k2. The reference impedance
RefR1 + jRefX1 is also calculated. After this the values are downloaded to the parameter setting
in PCM600. From PCM600 the settings are downloaded to IED.
Now the reference impedance is derived for one operational state. It might be necessary to
make measurements to derive reference impedance for other operational cases. For
information on this, see Commissioning below.
Commissioning
Different operating conditions of the machine may require different reference impedances.
If a particular operating condition of the generator requires a second reference impedance,
the Commissioning tab of ICT is used to define and save the second reference.
If more than one reference impedance are to be used, there must be a logic configured to
detect when the generator is in such condition and change the reference.
Monitoring
The Monitoring tab of ICT offers the possibility to monitor several quantities during tests as
well as in normal operating condition in order to evaluate the behavior of the protection
function. It can help in the identification of the operating conditions, where a change of
reference impedance is required.
Section 6
1MRK 502 067-UEN B
Calibrating injection based sensitive rotor earth fault protection
52
Commissioning manual
