Siemens 7SC80 Manual page 209

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 2-58
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
Ferraris- disk, and the time response is adapted. This ensures a proper simulation of the temperature rise of
the protected object even for extremely fluctuating unbalanced load values. Reset begins as soon as 90 % of
the setting value is reached, in accordance with the dropout curve of the selected characteristic. In the range
between the dropout value (95 % of the pickup value) and 90 % of the setting value, the incrementing and
decrementing process is in idle state.
Disk emulation offers advantages when the behavior of the negative sequence protection must be coordi-
nated with other relays in the system based on electromagnetic measuring principles.
Logic
The following figure shows the logic diagram for the negative sequence protection function. The protection
may be blocked via a binary input. This resets pickup and time elements and clears measured values.
SIPROTEC Compact, 7SC80, Manual
E50417-G1140-C486-A8, Edition 07.2017
Inverse time characteristic for negative sequence protection
Functions
2.9 Negative Sequence Protection 46
209