Siemens 7SJ82 Manual page 778

Protection and Automation Functions
6.34 Underfrequency Load Shedding
The following figure shows 2 application scenarios of protection devices with the Underfrequency load shed-
ding function.
[dw_UFLS_positive power direction, 1, en_US]
Figure 6-217
Dotted arrow: Standard forward direction of the protection functionality
Solid arrow:
The standard forward direction of the protection functionality is from the busbar to the protected object which
is the transformer for device 1 or the feeder for device 2. The standard forward direction of the protection
functionality is configured via the (_:8881:116) Neutr.point in dir.of ref.obj parameter of the
measuring point I-3ph (see chapter
(I-3ph)). For the load-shedding function, the positive active-power flow direction can differ from the standard
forward direction of the protection functionality, such as for device 1. To adapt the function to this condition,
the Positive power direction parameter is used. With the Positive power direction parameter,
you can set the positive active-power flow direction either to the same as or to the inverse of the standard
forward direction.
•
For device 1, set the Positive power direction parameter to inv. to CT neu.pnt sett..
Then, the positive active-power flow direction of the power criterion is opposite to the standard forward
direction of the protection functionality. Consequently, the Underfrequency load shedding function
sheds the medium-voltage busbar when the positive power-flow direction is from the high-voltage
busbar to the medium-voltage busbar.
•
For device 2, set the Positive power direction parameter to acc. to CT neu.pnt sett..
Then, the positive active-power flow direction of the power criterion is the same as the standard forward
direction of the protection functionality. Consequently, the Underfrequency load shedding function
sheds the feeder when the positive power-flow direction is from the medium-voltage busbar to the
feeder.
778
Application Scenarios
Positive active-power flow direction
6.1.4 Application and Setting Notes for Measuring Point Current 3-Phase
SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017