Siemens 7SJ82 Manual page 362

Protection and Automation Functions
6.4 Voltage-Dependent Overcurrent Protection, Phases
•
Measurement of the fundamental comp.:
This method of measurement processes the sampled current values and filters out the fundamental
component numerically.
•
Measurement of the RMS value:
This method of measurement determines the current amplitude from the sampled values according to
the defining equation of the RMS value. Harmonics are included in the analysis.
Voltage-Dependent Pickup Threshold
The pickup threshold of the overcurrent stage depends on the voltage magnitude. A lower voltage decreases
the current pickup value (see
proportional dependence is realized.
[dwvolpic-220713-01.tif, 1, en_US]
Figure 6-27
With:
V
V
rated
PU sett.
PU(V)
The minimum current pickup threshold value is 0.03 * Irated. This value cannot be decreased any further even
not by voltage-dependent pickup threshold factor.
Decreasing the pickup threshold is carried out phase-selectively. The assignment of voltages to current-
carrying phases is shown in
Table 6-1
Current
I
A
I
B
I
C
Pickup and Dropout Behaviors of the Inverse-Time Characteristic Curve According to IEC and ANSI
When the input variable exceeds the threshold value by a factor of 1.1, the inverse-time characteristic curve is
processed.
362
Figure 6-27). In the range between V/V
Voltage Influence of the Pickup Threshold
= Measured phase-to-phase voltage
= Rated voltage (parameter Rated voltage in the function block General of the protec-
tion function group)
= Pickup threshold setting (parameter address: _11491:3)
= Applied pickup threshold according to the voltage influence
Table 6-1.
Controlling Voltages in Relation to the Fault Current
= 1.00 to 0.25 a linear, directly
rated
Controlling Voltage
V
AB
V
BC
V
CA
SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017