Siemens SIPROTEC 7SD610 Manual page 158

Functions
2.11 Undervoltage and Overvoltage Protection (optional)
Overvoltage zero-sequence system 3U
Figure 2-60 depicts the logic diagram of the zero-sequence voltage stage. The fundamental component is nu-
merically filtered from the measuring voltage so that the harmonics or transient voltage peaks remain largely
eliminated.
The triple zero-sequence voltage 3·U
dress 3724). Combined with the associated time delays T 3U0> (address 3723) and T 3U0>> (address
3725), these stages form a two-stage overvoltage protection for the zero-sequence system. Here too, the drop-
out to pickup ratio can be set (3U0>(>) RESET, address 3729). Furthermore, a restraint delay can be config-
ured 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 asymmet-
rical voltage failure was detected („Fuse Failure Monitor", also see Section 2.15.1, margin heading „Fuse
Failure Monitor (Non-symmetrical Voltages))" or when the trip of the mcb for voltage transformers has been sig-
nalled via the binary input „>FAIL:Feeder VT" (internal indication „internal blocking").
The stages of the zero-sequence voltage protection are automatically blocked during single-pole automatic
reclose dead time to avoid pickup with the asymmetrical power flow arising during this state. If the device co-
operates 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 zero-sequence system must be
blocked via a binary input during single-pole tripping.
According to Figure 2-60 the device calculates the voltage to be monitored:
3·U = U + U
0 L1
This applies if no suitable voltage is connected to the fourth measuring input U
However, if the displacement voltage U
measuring input U
matically use this voltage and calculate the triple zero-sequence voltage.
= Uph / Udelta ·U
3·U
0
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.
158
0
is fed to the two threshold stages 3U0> (address 3722) and 3U0>> (ad-
0
+ U .
L2 L3
delta
of the device and this information was entered during configuration, the device will auto-
4
4
of the voltage transformer set is directly connected to the fourth
C53000-G1176-C145-6, Release date 02.2011
.
4
SIPROTEC, 7SD610, Manual