Functions
2.19 Undervoltage and Overvoltage Protection (optional)
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
366
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 2.24.1, 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 2-176 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 auto-
matically use this voltage and calculate 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.
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