Siemens siprotec 7SA6 User Manual page 397

Zero Sequence
System
Overvoltage
Undervoltage
Phase–Earth
7SA6 Manual
C53000-G1176-C133-1
the other being 8!! (address ) with a short delay time 7 8!! (address )
for high asymmetrical voltages.
Note that the negative sequence system is established according to its defining
⋅|U
1
equation U = /
2 3 L1
exchanged phases this is equivalent to the phase–to–earth voltage value.
The drop-off to pick-up ratio 8! ! 5(6(7) can be set in address  . This setting
can only be changed with DIGSI
The zero sequence voltage stage can be switched 2Q or 2II in address . In ad-
dition, this stage can also be selected to $ODUP 2QO\ i.e. these stages operate and
issue alarms only. This protection function can be used for any other single-phase
voltage which is connected to the fourth voltage measurement input U
Section 6.1.1 and see margin heading "Voltage Transformer Connection").
The settings of the voltage threshold and the timer values depend on the type of ap-
plication. Here no general guidelines can be established. Generally, with a sensitive
setting of 8! (address ), i.e. close to operational values that are to be expect-
ed, not only the time delay 7 8 (address ) must be greater, but also the reset
ratio 8 5HVHW 5DWLR (address ) must also be as large as possible. Usually
the presetting is sufficient. This setting can only be changed with DIGSI
ditional Settings".
Similar considerations apply if this voltage stage is used for a different voltage at the
measuring input U .
4
When setting the voltage values please observe the following:
• If the U
-voltage of the set of voltage transformers is connected to U
en
was already set in the power system data 1 (refer also to Section 6.1.1 under
margin heading "Voltage Transformer Connection", U4 transformer = 8GHOWD
WUDQVI), the device multiplies this voltage by the matching ratio 8SK  8GHOWD
(address ), usually with 1.73. Therefore the voltage measured is √3 · U
. When the voltage triangle is fully displaced, the voltage will be √3-times the
3 . U
0
phase-to-phase voltage .
• If any other voltage is connected to U
if this was already set in the power system data 1 (refer also to Section 6.1.1,
"Voltage Transformer Connection", e. g. 8 WUDQVIRUPHU = 1RW FRQQHFWHG or
8 WUDQVIRUPHU = 8V\QF WUDQVI), the device calculates the zero sequence
voltage according to its definition: 3 · U
triangle is fully displaced, the voltage will be √3-times the phase-to-phase voltage .
• If any other voltage is connected to U
this was already set in the power system data 1 (refer also to Section 6.1.1, "Voltage
Transformer Connection", i. e. 8 WUDQVIRUPHU = 8[ WUDQVIRUPHU), this
voltage will be used for the voltage stages without any further factors. This "zero
sequence voltage protection" then is, in reality, a single-phase voltage protection for
any kind of voltage at U
The phase undervoltage stages can be switched 2Q or Off in address  8SK
H . In addition to this, you can set $ODUP 2QO\, 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
) operates with the longer set time value 7 8SKH (address ) for a slight
undervoltages. However, it must not be set above the admissible undervoltage. In
⋅U
2
+ a + a⋅U |. For symmetrical voltages and two
L2 L3
®
4 under "Additional Settings".
, which is not used for voltage protection, and
4
= IU
0
, which is used for voltage protection, and if
4
.
4
. (Also refer to
4
+ U + U I. When the voltage
L1 L2 L3
Functions
®
4 under "Ad-
and if this
4
=
en
6-215