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Figure 2-26
Logic diagram of the undervoltage protection for positive sequence voltage system
During single-pole dead time for automatic reclosure the stages of the undervoltage protection are automati-
cally blocked in the positive sequence system so that they do not respond to the reduced voltage caused by
the disconnected phase in case the voltage transformers are located on the outgoing side.
This automatic blocking function requires the condition of the system to be detected without doubt. This means
that it is only active if all three current and voltage transformers are connected.
Single-Phase Voltage Connection
Please bear in mind that the device is designed for a three-phase voltage connection. Single-phase connection
is also possible but no adjustments have been made in this respect. This must be taken into consideration when
selecting the stage and the pickup value.
Operation Without Current Transformer Connections
The 7VK61 relay can also be operated without current transformer connections. This is achieved by setting pa-
rameter 107 CT CONNECTION = NO during configuration. For the undervoltage protection this has the conse-
quence that the current criterion cannot become active and associated parameters are hidden.
SIPROTEC, 7VK61, Manual
C53000-G1176-C159-3, Release date 05.2009
2.5 Under and over-voltage protection (optional)
Functions
105
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