Siemens siprotec 7SA522 - Page 281

2.15 Undervoltage and overvoltage protection (optional)
281
7SA522 Manual
C53000-G1176-C155-3
For symmetrical voltages an increase of the positive sequence system corresponds to
an AND gate of the voltages. These stages are particularly suited to the detection of
steady-state overvoltages on long, weak-loaded transmission lines (Ferranti effect).
Here too, the 8! stage (address ) with a longer delay time 78! (address
) is used for the detection of steady-state overvoltages (some seconds), the
8!! stage (address ) with the short delay time 78!! (address ) is used
for the detection of high overvoltages that may jeopardize insulation.
Please note that the positive sequence system is calculated according to its definition
equation U
1
=
1
/
3
·|U
L1
+a·U
L2
+a
2
·U
L3
|. For symmetrical voltages this is equivalent to
a phase-to-earth voltage.
If you want the voltage at the remote line end to be decisive for overvoltage detection,
you use the compounding feature. To do so, you must have set during the configura-
tion of the protective functions (Section 2.1.1.2) address  8292/7$*( to
(QDEOZFRPS (enabled with compounding).
In addition, the compounding feature needs the line data, which have bee set in the
3RZHU6\VWHP'DWD (Section 2.1.5.1): at address  or  [, address
 or  F and address  or  /LQH/HQJWK, and at address 
/LQH$QJOH. These data are vital for a correct compounding calculation. If the values
provided here do not correspond to real conditions, the compounding may calculate a
too high voltage at the remote end, which causes the protection to pick up immediately
as soon as the measured values are applied. In such a case, the pickup state can only
be reset by switching off the measuring voltage.
You can activate the compounding separately for each of the U1 voltages 21 or 2)):
for the 8! stage at address  8!&RPSRXQG and for the 8!! stage at address
 8!!&RPSRXQG.
The drop-off to pick-up ratio (address  8!!5(6(7) is set as high as possible
with regard to the detection of even small steady-state overvoltages. This setting is
only possible via DIGSI
®
at "Additional Settings".
Overvoltage Nega-
tive Sequence
System U
2
The negative sequence system voltage stages detect asymmetrical voltages. If such
voltages shall cause tripping, set the address  8!! to 21. If such a condition
shall only lead to output of an alarm, set the address  8!! to $ODUP2QO\,
in all other cases set it to 2)).
This protective function also has two stages, one being 8! (address ) with a
greater time delay 78! (address ) for steady-state asymmetrical voltages and
the other being 8!! (address ) with a short delay time 78!! (address )
for high asymmetrical voltages.
Please note that the negative sequence system is calculated according to its definition
equation U
2
=
1
/
3
·|U
L1
+a
2
·U
L2
+a·U
L3
|. For symmetrical voltages and two swapped
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
is only possible via DIGSI
®
at "Additional Settings".
Zero Sequence
System
Overvoltage
The zero sequence voltage stages can be activated at address  8!!RU
8[ 21- oder 2)). They can also be set to $ODUP2QO\, i.e. these stages operate
and send alarms but do not generate any trip commands. This protection function can
be used for any other single-phase voltage which is connected to the fourth voltage
measurement input U
4
. Also refer to Section 2.1.3.1 under margin header “Voltage
Transformer Connection”.