Inverse Time Overcurrent Protection 51V (Voltage-Controlled/Voltage-Restraint) - Siemens 7SC80 Manual

% of the pickup value) and 90 % of the setting value, the incrementing and the decrementing processes are in
idle state.
Disk emulation offers advantages when the overcurrent relay elements must be coordinated with conven-
tional electromechanical overcurrent relays located towards the source.
For recloser characteristic curves, an element drops out immediately after the value has fallen below a
threshold.
Minimum Operating Time
The minimum operating time defines the minimum interval for tripping the inverse element. When an inverse
element picks up, an individual time 51-1 Min O. T, 51-2 Min O. T, 51-3 Min O. T, 51-4 Min O.
T, 51N-1 Min O. T, 51N-2 Min O. T, 51N-3 Min O. T, 51N-4 Min O. T starts. The inverse element
can only trip after the minimum operating time elapses.
Inverse Time Overcurrent Protection 51V (Voltage-Controlled/Voltage-
2.2.6
Restraint)
Undervoltage Consideration
The inverse time overcurrent protection is provided with an undervoltage detection that can be disabled
(address 1223 VOLT. INFLUENCE). This function can influence overcurrent detection by means of two
different methods:
•
Voltage controlled: If a set voltage threshold is undershot, the overcurrent element is released.
•
Voltage restraint:The pickup threshold of the overcurrent element depends on the voltage magnitude. A
lower voltage decreases the current pickup value (see
to 0.25, a linear, directly proportional dependence is realized, and therefore the following applies:
[spannungsabhaengigkeit-des-anregewertes, 1, en_US]
Figure 2-15
NOTE
i
i
In the overcurrent protection 51 which is enabled with 51V voltage restraint option, the 51 PICKUP value
must be set to be higher than 0.05 I
The 51 PICKUP value is decreased proportional to the voltage decrease. Consequently, for constant current I
the Ι/ 51 PICKUP ratio is increased and the tripping time is reduced. Compared with the standard curves repre-
sented in Section "Technical Data", the tripping curve shifts to the left side as the voltage decreases.
SIPROTEC Compact, 7SC80, Manual
E50417-G1140-C486-A8, Edition 07.2017
Voltage influence of the pickup value
.
Nom
2.2 Overcurrent Protection 50, 51, 50N, 51N
Figure 2-15). In the range between V/V
Functions
= 1.00
Nom
81