7SR18 Applications Guide
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9.2 Current Transformer Supervision
When a CT fails, the current levels seen by the protection become unbalanced, however this condition would also
occur during a system fault. Depending upon the relay model different methods are used to determine the
condition, depending upon the measured quantities available.
Current Transformer Supervision (60CTS – 7SR18 without VTs)
Following a CT Failure, if one or two of the three-phases falls below the CT supervision setting the element will
operate.
Operation is subject to a time delay to prevent operation for transitory effects.
A 3-phase CT failure is considered so unlikely (these being independent units) that this condition is not tested for.
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