Capacitor-bank tap voltage as phase-to-phase voltage:
(it equals a phase-to-ground voltage of 13.28 kV)
23 kV
Voltage matching factors are set as: 345 kV/23 kV = 15
The voltage measuring points must be set as indicated in the figure:
Busbar transformer, rated primary voltage: 345 kV
Busbar transformer, rated secondary voltage: 110 V
Transformer to tap the voltage, rated primary voltage: 22 kV
Transformer to tap the voltage, rated secondary voltage: 110 V
Under normal operation, these settings result in a differential voltage of approximately 0 V and in the primary
and secondary measured voltage values as indicated in the 7.7.3.1 Description.
NOTE
The sound secondary tap voltage must not be smaller than 1 V. Otherwise the function cannot work prop-
erly. Fulfill this condition by applying an appropriate voltage transformer for the tap voltage. Siemens
recommends applying a tap voltage transformer which provides under normal operation a secondary
voltage in the area of the rated secondary voltage.
EXAMPLE
In the grounded system:
Ratio of the capacitor-bank busbar voltage to the tap voltage (matching
factor k):
400 kV/400 V = 1000
Busbar transformer, rated primary voltage: 400 kV
Busbar transformer, rated secondary voltage: 100 V
To ensure an optimal tap-voltage measurement, the following transformer ratio is recommended:
Transformer to tap the voltage, rated primary voltage: 400 V
Transformer to tap the voltage, rated secondary voltage: 100 V
Capacitor Bank Protection
7.7 Voltage Differential Protection for Capacitors
SIPROTEC 5, Overcurrent Protection, Manual 1039
C53000-G5040-C017-8, Edition 07.2017
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