Siemens 7SC80 Manual page 80

Functions
2.2 Overcurrent Protection 50, 51, 50N, 51N
[Lo_51N-1, 1, en_US]
Figure 2-14
If parameter 1313 MANUAL CLOSE is set to 51N-1 instant., 51N-2 instant., 51N-3 instant.,
51N-4 instant., and manual close detection is used, a pickup causes instantaneous tripping even if the
element is blocked via a binary input.
The same applies to 79 AR 51N-1 inst., 79 AR 51N-2 inst., 79 AR 51N-3 inst., 79 AR 51N-4 inst..
Dropout Behavior
For the ANSI or IEC characteristics, you can select whether an element drops out instantaneously after a
threshold has been undershot or whether dropout is performed by means of disk emulation. "Instantaneous"
means that the picked-up element drops out when 95 % of the pickup value is undershot. For a new pickup,
the time delay 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. Reset begins as soon as 90 % of the setting value is undershot,
in accordance to the dropout curve of the selected characteristic. In the range between the dropout value (95
80
Logic Diagram of the 51N-1 Inverse Time Overcurrent Protection for Ground
SIPROTEC Compact, 7SC80, Manual
E50417-G1140-C486-A8, Edition 07.2017