(1) Description of Operation 7SR224
©2009 Siemens Protection Devices Limited Page 55 of 66
5.3 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 A binary or virtual input.
&
60CTS Delay
VL1
VL2
VL3
NPS
Filter
V2
60CTS Vnps
<
IL1
IL2
IL3
NPS
Filter
I2
60CTS Inps
>
&
Inhibit 60CTS
60CTS Element
Enabled
Disabled
&
60CTS Operated
Figure 5.3-1 Logic Diagram: CT Supervision Function (60CTS)
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