Ct Supervision (60Cts & 60Cts-I); 60Cts-I) - 7Sr21 & 7Sr22; 60Cts) - 7Sr22; Figure 5.4-1 Logic Diagram: Ct Supervision Function (60Cts-I) - 7Sr21 & 7Sr22 - Siemens 7SR21 Manual

5.3 CT Supervision (60CTS & 60CTS-I)
The relay has two methods of detecting a CT failure, depending on the relay variant.
5.4 (60CTS-I) – 7SR21 & 7SR22
The current from each of the Phase Current Transformers is monitored. If one or two of the three input currents
falls below the CT supervision current setting CTS-I for more than 60CTS-I Delay then a CT failure output
(60CTS-I Operated) is given. If all three input currents fall below the setting, CT failure is not raised.
Operation of the CT supervision elements can be inhibited from:
Inhibit 60CTS-I
Figure 5.4-1 Logic Diagram: CT Supervision Function (60CTS-I) – 7SR21 & 7SR22
5.5 (60CTS) – 7SR22
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 CT supervision elements can be inhibited from:
Inhibit 60CTS
Figure 5.5-1 Logic Diagram: CT Supervision Function (60CTS) – 7SR22
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A binary or virtual input.
A binary or virtual input.
7SR21 & 7SR22 Argus Description of Operation
Chapter 1 Page 63 of 71