Settable Dropout Times
Pickup stabilization for the definite-time tripping characteristic 46-1, 46-2 can be accomplished by means of
settable 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.
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 characteristic also definite time elements 46-2 PICKUP and 46-1 PICKUP are available
(see a foregoing paragraph).
Pickup and Tripping
The negative sequence current Ι is compared to the setting value 46-TOC PICKUP. When the negative
sequence 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 characteristic selected. When tripping time is
reached, a tripping command is issued. The characteristic curve is illustrated in the following Figure.
[abhaeng-ausl_charakt-des-schieflastschutzes-260602-kn, 1, en_US]
Figure 2-53 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.
Dropout for ANSI Curves
When using an ANSI curve it can be selected whether the dropout of the element is to occur instantaneously
or whether dropout is to be performed by means of the disk emulation mechanism. „Instantaneous“ means
that the drop out will occur when a 95 % of the pickup value is reached. For a new pickup the time counter
starts at zero.
The disk emulation evokes a dropout process (timer counter is decrementing) which begins after de-energiza-
tion. This process corresponds to the reset of a Ferraris-disk (explaining its denomination "disk emulation"). In
case several faults occur in succession, the "history" is taken into consideration due to the inertia of the
2.7.2
Functions
2.7 Negative Sequence Protection 46
138 SIPROTEC 4, 7SJ62/64, Manual
C53000-G1140-C207-8, Edition 08.2016
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