2 Functions
282
7SA522 Manual
C53000-G1176-C155-3
This protective function also has two stages. The settings of the voltage threshold and
the timer values depend on the type of application. Here no general guidelines can be
established. The stage 8! (address ) is usually set with a high sensitivity and
a longer delay time 78! (address ). The 8!! stage (address ) and
its delay time 78!! (address ) allow you to implement a second stage with
less sensitivity and a shorter delay time.
Similar considerations apply if this voltage stage is used for a different voltage at the
measuring input U
4
.
Since the time delays of the zero sequence voltage stages are very stable due to the
measurement repetition, the sensitivity can be set quite high. This stabilization can be
deactivated at address 8!!6WDELO if a shorter pickup time is required.
This setting is only possible via DIGSI
®
at "Additional Settings". Please keep in mind
that it does not make sense to combine a sensitive setting with a short pickup time.
The drop-off to pick-up ratio 8!!5(6(7 can be set in address . This
setting is only possible via DIGSI
®
at "Additional Settings".
When setting the voltage values please observe the following:
• If the voltage U
4
is connected to the voltage U
en
of the set of voltage transformers
and this has been specified when setting the Power System Data 1 (see Section
2.1.3.1 under margin header “Voltage Transformer Connection”, address 8
WUDQVIRUPHU = 8GHOWDWUDQVI), the device multiplies the voltage connected
there with the matching factor 8SK8GHOWD (address ), i.e. normally with
1.73. The voltage measured is thus √3
·U
en
= 3·U
0
. If the symmetrical voltage delta
is completely displaced, it will be √3
times the phase-phase voltage.
• If the voltage U
4
is connected to any other voltage which is not used for voltage pro-
tection, and this has been specified when setting the Power System Data 1 (see
Section 2.1.3.1 under margin header “Voltage Transformer Connection”, z.B. 8
WUDQVIRUPHU = 8V\QFWUDQVI oder 8WUDQVIRUPHU = 1RWFRQQHFWHG),
the device calculates the zero sequence voltage from the phase voltages according
to their definition 3·U
0
=|U
L1
+U
L2
+U
L3
|. If the symmetrical voltage delta is com-
pletely displaced, it will be √3
times the phase-phase voltage.
•If U
4
is connected to any other AC voltage which is used for voltage protection, and
this has been specified when setting the Power System Data 1 (see Section 2.1.3.1
under margin header “Voltage Transformer Connection”, 8WUDQVIRUPHU = 8[
WUDQVIRUPHU), this voltage will be used for the voltage stages without any further
factors. This “zero sequence voltage” is then actually, a single-phase voltage pro-
tection for any kind of voltage at U
4
. Please note that with a sensitive setting, i.e.
with a setting close to the voltages to be expected in operation, you need to set not
only the delay time 78! (address ) but also the pickup/dropout ratio
8!!5(6(7 (address ) as high as possible.
Undervoltage
Phase–Earth
The phase voltage stages can be switched 21 or 2)) under address 8SK
H. In addition to this you can set $ODUP2QO\, i.e. these stages operate and
send alarms but do not generate any trip commands.
This undervoltage protection function has two stages. The 8SKH stage (address
) with a longer setting of the time 78SKH (address ) operates in the case
of minor undervoltages. However, the value set here must not be higher than the un-
dervoltage permissible in operation. In the presence of higher voltage dips, the 8SK
H stage (address ) with the delay 78SKH (address ) becomes active
The settings of the voltages and times depend on the intended use; therefore no
general recommendations for the settings can be given. For load shedding, for exam-
ple, the values are often determined by a priority grading coordination chart. In case
To Next Page
Loading...
Need help?
General
