Siemens 7SR51 - Page 184

Parameter: 46DT-n Setting
•
Default setting: 0.1 x I
n
(0.1 I
rated
)
The operate level depends on the respective application. A threshold value of 10 % is a practicable value
for fault indications of electrical machines.
Parameter: 46DT-n Delay (DTL)
•
Default setting: 0.02 s
The setting of the operate delay depends on the application. Grading with other devices in the power-
system must be considered.
For motors, the time depends on the permissible withstand time for the set unbalanced load.
Parameter: 46IT-n Setting
•
Default setting: 0.25 x I
n
(0.25 I
rated
)
The operate level depends on the respective application. A threshold value of 10 % is a practicable value
for fault detection for different applications.
Parameter: 46-IT-n Char
•
Default setting: IEC-NI
Selects the operating characteristic curve required for the specific application.
Parameter: Time Mult (IEC/ANSI)
•
Default setting: 1
The set value for the time multiplier is derived from the time-grading study of the electrical network or
protected plant.
Settings Example
Backup Protection with a 3-Winding Transformer
The function Negative Sequence Overcurrent Protection can be used to provide a transformer sensitive backup
protection on the supply side as it will detect low 1-phase and 2-phase short circuit currents. Also on the low-
voltage side, 1-phase short circuits can be used, which do not create a zero-sequence system in the current on
the upper-voltage side (for example in vector group Dyn).
The following example explains the achieved sensitivity.
[sc_Function46SettingsExample, 1, --_--]
Figure 5-9 1-Phase and 2-Phase Short Circuit on Transformer
Protection and Automation Functions
5.7 46 Negative-Sequence Overcurrent Protection
184 Reyrolle 7SR5, Overcurrent Protection Device, Device Manual
C53000-G7040-C014-1, Edition 11.2019