2.11 Undervoltage and Overvoltage Protection (optional)
165
7SD610 Manual
C53000-G1176-C145-4
If the voltage transformers are located on the line side, the measuring voltages will be
missing when the line is disconnected. To avoid that the undervoltage levels in these
cases are or remain picked up, the current criterion CURR.SUP. Uphe< (address
3758) is switched ON. With busbar side voltage transformers it can be switched OFF.
However, if the busbar is dead, the undervoltage protection will pick up and expire and
then remain in a picked-up state. It must therefore be ensured in such cases that the
protection is blocked by a binary input.
Phase-phase und-
ervoltage
Basically, the same considerations apply as for the phase voltage stages. These
stages may replace the phase voltage stages or be used additionally. Depending on
your choice, set address 3761 Uph-ph<(<) to ON, OFF, Alarm Only or U<Alarm
U<<Trip.
As phase–to–phase voltages are monitored, the phase–to–phase values are used for
the settings Uph-ph< (address 3762) and Uph-ph<< (address 3764).
The corresponding times delay are T Uph-ph< (address 3763) and T Uphph<< (ad-
dress 3765).
The dropout to pickup ratio Uphph<(<) RESET can be set in address 3769. This pa-
rameter can only be altered in DIGSI at Display Additional Settings.
If the voltage transformers are located on the line side, the measuring voltages will be
missing when the line is disconnected. To avoid that the undervoltage levels in these
cases are or remain picked up, the current criterion CURR.SUP.Uphph< (address
3768) is switched ON. With busbar side voltage transformers it can be switched OFF.
However, if the busbar is dead, the undervoltage protection will pick up and expire and
then remain in a picked-up state. It must therefore be ensured in such cases that the
protection is blocked by a binary input.
Undervoltage posi-
tive sequence
system U
1
The positive sequence undervoltage stages can be used instead of or in addition to
previously mentioned undervoltage stages. Depending on your choice, set address
3771 U1<(<) to ON, OFF, Alarm Only or U<Alarm U<<Trip.
Basically, the same considerations apply as for the other undervoltage stages. Espe-
cially in case of stability problems, the positive sequence system is advantageous,
since the positive sequence system is relevant for the limit of the stable energy trans-
mission.
To achieve the two-stage condition, the U1< stage (address 3772) is combined with a
greater time delay T U1< (address 3773), and the U1<< stage (address 3774) with a
shorter time delay T U1<< (address 3775).
Note that the positive sequence system is established according to its defining equa-
tion U
1
=
1
/
3
·|U
L1
+a·U
L2
+a
2
·U
L3
|. For symmetrical voltages this is equivalent to a
phase-earth voltage.
The dropout to pickup ratio U1<(<) RESET can be set in address 3779. This param-
eter can only be altered in DIGSI at Display Additional Settings.
If the voltage transformers are located on the line side, the measuring voltages will be
missing when the line is disconnected. To avoid that the undervoltage levels in these
cases are or remain picked up, the current criterion CURR.SUP.U1< (address 3778)
is switched ON. With busbar side voltage transformers it can be switched OFF. How-
ever, if the busbar is dead, the undervoltage protection will pick up and expire and then
remain in a picked-up state. It must therefore be ensured in such cases that the pro-
tection is blocked by a binary input.
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