Siemens siprotec 7SD5, Руководство пользователя, Страница: 329 / 698

2.17 Undervoltage and Overvoltage Protection (optional)
329
7SD5 Manual
C53000-G1176-C169-1
Even during single-pole dead time (with internal automatic reclosure function) the
stages of the negative sequence overvoltage protection are automatically blocked
since arising negative sequence values are only influenced by the asymmetrical
power flow, not by the fault in the system. If the device cooperates with an external
automatic reclosure function, or if a single-pole tripping can be triggered by a different
protection system (working in parallel), the overvoltage protection for the negative se-
quence system must be blocked via a binary input during single-pole tripping.
Overvoltage Zero
Sequence System
3U
0
Figure 2-136 depicts the logic diagram of the zero sequence voltage stage. The fun-
damental frequency is numerically filtered from the measuring voltage so that the har-
monics or transient voltage peaks remain largely harmless.
The triple zero sequence voltage 3·U
0
is fed to the two threshold stages
3U0>
and
3U0>>
. Combined with the associated time delays
T 3U0>
and
T 3U0>>
these stages
form a two-stage overvoltage protection for the zero sequence system. Here too, the
drop-off to pickup ratio can be set (
3U0>(>) RESET
). Furthermore, a restraint delay
can be configured which is implemented by repeated measuring (approx. 3 periods).
The overvoltage protection for the zero sequence system can also be blocked via a
binary input
„>3U0>(>) BLK“
. The stages of the zero sequence voltage protection
are automatically blocked as soon as an asymmetrical voltage failure was detected
(„Fuse–Failure–Monitor“, also see Section 2.22.1, margin heading „Fuse Failure
Monitor (Non-symmetrical Voltages))“ or when the trip of the mcb for voltage trans-
formers has been signalled via the binary input
„>FAIL:Feeder VT“
(internal indi-
cation „internal blocking“).
The stages of the zero sequence voltage protection are automatically blocked (with
the internal automatic reclosure function) during single-pole automatic reclose dead
time to avoid pickup with the asymmetrical power flow arising during this state. If the
device operates with an external automatic reclosure function or if single-pole tripping
can be triggered by a different protection system (operating in parallel), the overvolt-
age protection for the zero sequence system must be blocked via a binary input during
single-pole tripping.
According to Figure 2-136 the device calculates the voltage to be monitored:
3·U
0
= U
L1
+ U
L2
+ U
L3
.
This applies if no suitable voltage is connected to the fourth measuring input U
4
.
However, if the displacement voltage U
Delta
of the voltage transformer set is directly
connected to the fourth measuring input U
4
of the device and this information was
entered during configuration, the device will automatically use this voltage and calcu-
late the triple zero sequence voltage.
3·U
0
=
Uph / Udelta
·U
4
Since the voltage transformation ratio of the voltage transformer set is usually
the factor is set to
Uph / Udelta
= 3/
√
3 =
√
3 = 1.73. For more details, refer to
General Power System Data (Power System Data 1)
in Section 2.1.4.1
at margin heading „Voltage Connections“ via address
211
.
www
. ElectricalPartManuals
. com