Busbar Vt Fail (60Vtf-Bus); Ct Supervision (60Cts); Figure 5.3-1 Logic Diagram: Ct Supervision Function (60Cts) - Siemens 7SR224 Technical Manual

5.3

Busbar VT Fail (60VTF-Bus)

When the optional synchronising function is fitted, the synchronising voltage transformer is utilised to provide an
additional monitoring function to check the validity of the measured line and busbar voltages. When the circuit
breaker is closed, both voltages should be either Live or Dead. If the Bus voltage indicates that the VT is Dead
but the corresponding Line voltage is Live, this raises the Bus VT Fail output. A time delay setting is provided to
avoid spurious operations during transient switching conditions. Additionally, this output can be enabled by a
setting, 79 LO Bus VT Fail, to apply a Lockout signal to the autoreclose function so that a sequence will not be
attempted after a trip occurs if it is known that the voltage measurement is not reliable. A similar setting is
available, 79 LO Line VT Fail, which when Enabled will provide a Lockout for a Line VT failure detected by the
60VTS function.
5.4

CT Supervision (60CTS)

Normally the presence of negative phase sequence (NPS) current in a power system is accompanied by NPS
voltage. The presence of NPS current without NPS voltage is used to indicate a current transformer failure.
The element has a setting for NPS current level 60CTS Inps and a setting for NPS voltage level 60CTS Vnps If
the negative sequence current exceeds its setting while the negative sequence voltage is below its setting for
more than 60CTS Delay then a CT failure output (60CTS Operated) is given.
Operation of the under/over voltage elements can be inhibited from:
Inhibit 60CTS
Figure 5.4-1 Logic Diagram: CT Supervision Function (60CTS)
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A binary or virtual input.
7SR224 Argus Description of Operation
Chapter 1 Page 59 of 70