Siemens siprotec SJ62 User Manual page 273

2 Functions
Settings
Renaming Messag-
es, Checking Allo-
cations
Additional Informa-
tion
271
The pickup thresholds, delay times and dropout ratios of the flexible protection func-
tion are set in the DIGSI „Settings" dialog box.
The function's pickup threshold is set in parameter P.U. THRESHOLD. The TRIP
delay time is set in parameter T TRIP DELAY. Both setting values must be selected
to suit the required application.
The pickup may be delayed via parameter T PICKUP DELAY. This parameter is
usually set to zero for protective applications (default) since a protective function is
desired to pick up as soon as possible. A setting other than zero may be useful if it is
not desired that a fault log is opened each time the pickup threshold is briefly violated.
This is the case, for example, with line protection, or if the function is used not for pro-
tection but for monitoring purposes.
When setting small power thresholds, it must be observed that a power calculation re-
quires at least a current of 0.03 I
rents.
Dropout of the pickup condition can be delayed in parameter T DROPOUT DELAY. This
setting, too, is set to zero by default. A setting other than zero may be useful if the
device interacts with electro-mechanical devices whose dropout times are significantly
longer than those of the numerical protection device (see also section 2.2). When
using the dropout delay time, it is recommended to set it shorter than the TRIP delay
time to avoid "race conditions" of the two times.
In parameter BLK.by Vol.Loss, the user can specify whether a function, whose
measured quantity is based on a voltage measurement (voltage measured quantities,
P forward, P reverse, Q forward, Q reverse and power factor), is blocked in the event
of a measuring voltage failure (setting Yes) or not (setting No).
The function's dropout ratio can be set in parameter DROPOUT RATIO. The standard
dropout ratio of protective functions is 0.95 (default). When using the function as
power protection, the dropout ratio should be set to at least 0.9. The same applies
when using the symmetrical components of current and voltage. If the dropout ratio is
reduced, it is recommended to test pickup of the function for any signs of "chattering".
Moreover, it is important that no dropout ratio is configured for the measured values of
frequency (f) and frequency change (df/dt) since it employs a fixed dropout difference.
After setting a flexible function, the following additional steps are necessary:
• Open the Configuration Matrix in DIGSI.
• Rename the neutral message texts to suit the application.
• Check configurations for contacts and in operating and fault buffers or set according
to the requirements.
The following additional note must be observed:
• Since the power factor is not capable of distinguishing between capacitive and in-
ductive, the sign of the reactive power may be used as an additional criterion by
means of CFC.
. The power calculation is blocked for smaller cur-
Nom
SIPROTEC 4, 7SJ62/63/64 Handbuch
C53000-G1140-C147-A, Edition 07.2015