It is important that calibration steps (Step 1, Step 2 and Step 3) are
performed in the proper order. If not, the calibration might fail. If readings
are not stable during the step, a warning to repeat the step may be
suggested; the step shall be repeat in order to avoid that the calibration
fails.
4.
When the statistical error of the performed continuous measurements reaches an
acceptable value, the indicator bar reaches the stability region (turned green) and it is
allowed to select the Submit button.
Clicking the Submit button, the result is stored for later calculations. ICT automatically
shifts to the second calibration sub tab, Step2: Measurement 2.
Stability region
indicator bar
IEC11000047-1-en.vsd
GUID-3C7F0567-2367-46E4-9606-FCFC7408DAA0 V1 EN-US
Figure 22: ICT calibration tab 1 including the stability region indicator bar
5.
Connect a calibration resistance
Rcal between the neutral point of the generator and
ground; the value of the calibration resistance can be selected on the basis of the
impedance to ground of the stator:
2
stat
cal
stat
Z
R
Z
≤
≤ ⋅
IECEQUATION17022 V2 EN-US
The stator impedance to ground can be estimated by one of the below quantities:
•
The total impedance to ground of the stator windings at the injection frequency:
1
1
stat
stat
N
Z
j C
R
ω
=
+
IECEQUATION17023 V1 EN-US
where,
R
N
is the primary grounding resistor
C
stat
is the total capacitance to ground of all three stator windings and of equipment
connected to the terminal of the generator
•
The total impedance to ground of the stator windings at the injection frequency
taking into account the equivalent resistance R
N
, eq of the grounding resistor
transferred to the primary side of the grounding transformer:
1MRK 502 067-UEN B
Section 7
Calibrating injection based 100% stator earth fault protection
67
Commissioning manual
