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Figure 2-5
The device can fully function only if the secondary voltage that results from the nominal voltage on the primary
side lies within a certain range. If the primary nominal voltage at the voltage inputs causes a too small or too
high voltage, the function of the device will be blocked. This plausibility check is run each time the device starts
up based on the configured parameter values for the primary nominal voltage and the configured capacitance
values.
Note
The settings for the primary nominal voltage and the settings of the capacitance values must lead to a voltage
between 34 V and 140 V on the secondary side (voltage inputs of the device) with nominal voltage on the
primary side. Since the input voltages are phase-to-Ground voltages, the operational range for the input volt-
ages is hence 34 V / √3 to 140 V / √3 .
If this condition is not satisfied for at least one of the three voltage inputs, the device will generate the messages
„Device Failure" and 10036 „Capac.Par.Fail." after startup.
Note
Used bushing capacities have to be available exclusively to the connected 7Sx80. Connecting a parallel port,
e.g. on a capacitive voltage measuring device, at the same bushing capacities is not allowed.
Internal Normalization of the Measured Voltages
The capacitance values for the three voltage inputs will usually not be absolutely identical. From this we can
conclude that voltages identical on the primary side are mapped differently at the voltage inputs. The measured
voltages are normalized by the device so that the three phase-to-Ground voltages can still be linked by calcu-
lation (e.g. to calculate the phase-to-phase voltages of the positive sequence system and of the negative se-
quence system etc.). This normalization has the effect that the primary nominal voltage in the device leads to
voltage values that correspond to the configured secondary nominal voltage (parameter 203 Vnom
SECONDARY) even though the real voltages at the input terminals are different.
The setting of parameter 203 Vnom SECONDARY should be roughly equivalent to the voltage at the terminals
of the protection device at primary nominal voltage. If capacitive voltage measurement is selected, a setting
range of 34 V to 140 V is sufficient for this parameter.
SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A5, Release date 11.2012
Capacitive voltage measurement
Functions
2.1 General
45
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