Siemens 7SJ85 - Page 309

Broken-delta winding (for
example, grounding trans-
former in generator protection)
V
rated sec
= 500 V
The voltage input of the device is designed for a continuous operation,
using 230 V max. Therefore, the voltage on the broken-delta winding (500
V) is reduced to a 5:2 ratio, using an Ohmic divider. In order to calculate the
matching factor, the secondary voltage of 200 V will be applied.
Calculate the Matching ratio Vph / VN parameter as follows:
[fo_bsp2, 1, en_US]
Set Matching ratio Vph / VN = 0.866.
Interpretation of the result:
The zero-sequence voltage calculated from the phase-to-ground voltage is 57.73 V (= 100V/√3). The meas-
ured residual voltage is 200 V. The calculated adaptation factor is 0.866. The measured residual voltage is
converted to a zero-sequence voltage inside the device:
[fo_umrechnung2, 2, en_US]
i
i
NOTE
During the ground-fault test, the set adaptation factor can be checked by comparing the operational meas-
ured values. The operational measured values contain the calculated zero-sequence voltage V
0 sec
and the
measured residual voltage V
N sec
. Proceed with the compilation as follows:
The Matching ratio Vph / VN parameter is significant for the following functions:
•
Overvoltage protection with zero-sequence voltage/residual voltage
•
Measured-value supervision
•
Scaling of the faulty and measured values
Parameter: VT connection
•
Default setting (_:8911:104) VT connection = 3 ph-to-gnd volt. + VN
The parameter VT connection shows the connection type of the voltage transformer for the 3-phase
voltage measuring point. The parameter can be found in the DIGSI 5 project tree under Name of the device
→ Settings → Power system → Measuring point V 3-phase. You cannot change the connection type of the
voltage transformer in the power-system data.
You can change the connection type of the voltage transformer only under measuring point routing in
DIGSI 5. Under Name of the device → Measuring-points routing → Voltage measuring points, select the
desired connection type under Connection type. The following types of connections are possible:
•
3 ph-to-gnd volt. + VN
•
3 ph-to-gnd voltages
•
3 ph-to-ph volt. + VN
•
3 ph-to-ph voltages
•
2 ph-to-ph volt. + VN
Protection and Automation Functions
6.1 Power-System Data
SIPROTEC 5, Overcurrent Protection, Manual 309
C53000-G5040-C017-8, Edition 07.2017