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2 Functions
Figure 2-136
Logic diagram of the overvoltage protection for zero sequence voltage
Freely Selectable
As the zero sequence voltage stages operate separately and independent from the
Single–phase
other protective overvoltage functions they can be used for any other single–phase
Voltage
voltage. Therefore the fourth voltage input U
ingly (also see Section 2.1.2, „Voltage Transformer Connection").
The stages can be blocked via a binary input „>3U0>(>) BLK". Internal blocking is
not accomplished in this application case.
2.17.2 Undervoltage Protection
Undervoltage
Figure 2-137 depicts the logic diagram of the phase voltage stages. The fundamental
Phase–Earth
frequency is numerically filtered from each of the three measuring voltages so that har-
monics or transient voltage peaks are largely harmless. Two threshold stages Uph-
e< and Uph-e<< are compared with the voltages. If phase voltage falls below a
threshold it is indicated phase-segregated. Furthermore, a general pickup indication
„Uph-e< Pickup" „Uph-e<< Pickup" is given. The drop-out to pickup ratio can
be set ().
Every stage starts a time delay which is common to all phases. Expiry of the respective
time delay T Uph-e< or T Uph-e<< is signalled and results in the trip command
„Uph-e<(<) TRIP".
Depending on the configuration of the substations, the voltage transformers are
located on the busbar side or on the outgoing feeder side. This results in a different
330
of the device must be assigned accord-
4
C53000-G1176-C169-1
7SD5 Manual
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