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Functions
2.8 Undervoltage and Overvoltage Protection (optional) 27/59
[lo-uespg-null-20101108, 1, en_US]
Figure 2-49
Undervoltage Protection (ANSI 27)
2.8.2
Undervoltage Phase–Ground
Figure 2-50
depicts the logic diagram of the phase voltage elements. The fundamental frequency is numeri-
cally filtered from each of the three measuring voltages so that harmonics or transient voltage peaks are
largely harmless. Two threshold elements 27-1-Vph PICKUP (address 3752) and 27-2-Vph PICKUP
(address 3754) are compared with the voltages. If phase voltage falls below a threshold it is indicated phase-
segregated. Furthermore, a general pickup indication
each element. The dropout ratio can be set (27-Vph RESET, address 3759).
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 behavior of the undervoltage protection when the line
is de-energized. While the voltage usually remains present or reappears on the busbar side after a trip
command and opening of the circuit breaker, it becomes zero on the outgoing side. For the undervoltage
protection this results in a pickup state being present if the voltage transformers are on the outgoing side. If
this pickup must be reset, the current can be used as an additional criterion (current criterion CURR.SUP 27-
Vph, address 3758) to achieve this result. Undervoltage will then only be detected if, together with the under-
voltage condition, the minimum current PoleOpenCurrent of the corresponding phase is also exceeded.
This condition is communicated by the central function control of the device.
The undervoltage protection phase-to-ground can be blocked via a binary input
of the undervoltage protection are then automatically blocked if a voltage failure is detected ("Fuse-Failure-
112
Logic diagram of the overvoltage protection for zero sequence voltage
27-1-Vpg Pickup and 27-2-Vpg Pickup exists for
27-Vphg BLK . The elements
E50417-G1100-C474-A2, Edition 02.2018
SIPROTEC 4, 7SD80, Manual
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