Functions
2.6 Negative Sequence Protection 46
SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A5, Release date 11.2012
121
Settable Dropout Times
Pickup stabilization for the definite-time tripping characteristic 46-1, 46-2 can be accomplished by means of set-
table dropout times. This facility is used in power systems with possible intermittent faults. Used together with
electromechanical relays, it allows different dropout responses to be adjusted and a time grading of numerical
and electromechanical relays to be implemented.
2.6.2 Inverse Time Characteristic 46-TOC
The inverse time Element is dependent on the ordered device version. It operates with IEC or ANSI character-
istic tripping curves. The curves and associated formulas are given in the Technical Data. When programming
the inverse time Curve also definite time elements 46-2 PICKUP and 46-1 PICKUP are available (see a fore-
going paragraph).
Pickup and Tripping
The negative sequence current I2 is compared to the setting value 46-TOC PICKUP. When the negative se-
quence current exceeds 1.1 times the setting value, a pickup annunciation is generated. The tripping time is
calculated from the negative sequence current according to the Curve selected. When tripping time is reached,
a tripping command is issued. The characteristic curve is illustrated in the following Figure.
Figure 2-34 Inverse time characteristic for negative sequence protection
Dropout for IEC Curves
The Element drops out when the negative sequence current decreases to approx. 95% of the pickup setting.
The time delay resets immediately to be ready for another pickup operation.
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