Description
Logic of a Stage
[lo_NSP_Inverse, 1, en_US]
Figure 7-185
Logic Diagram of the Negative-Sequence Protection with Inverse-Time Characteristic Curve
Method of Measurement
The fundamental phasors are calculated from the 3-phase phase currents. Based on this, the negative-
sequence system and the positive-sequence system are calculated. Following this, the negative-sequence
current is normalized to the reference current. The selection of the reference current is made in the FB
General.
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 stage picks up, and the inverse-
time characteristic curve is processed. An integrating method of measurement totalizes the weighted time.
The weighted time results from the characteristic curve. For this, the time that is associated with the present
current value is determined from the characteristic curve. Once the weighted time exceeds the value 1, the
stage operates.
When the measured value falls below the pickup value by a factor of 0.95 (0.95 ⋅ 1.1 ⋅ threshold value), the
dropout is started. The pickup is indicated as clearing. You can influence the dropout behavior via setting
parameters. You can select between instantaneous dropout (totalized time is deleted) or dropout according to
the characteristic curve (reduction of totalized time depending on the characteristic curve). The dropout
7.25.7
Protection and Automation Functions
7.25 Negative-Sequence Protection
SIPROTEC 5, High-Voltage Bay Controller, Manual
875
C53000-G5040-C015-9, Edition 11.2017
Содержание 6MD85
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