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Stage with Inverse-Time Characteristic Curve
6.17.5
6.17.5.1
Description
Logic of a Stage
[lo_NSP_Inverse, 1, en_US]
Figure 6-155
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
SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017
Logic Diagram of the Negative-Sequence Protection with Inverse-Time Characteristic Curve
Protection and Automation Functions
6.17 Negative-Sequence Protection
639
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