Signaling and Indication

Triggering of the CTS function is signaled by multiple signals as well as by single signals referring to the respective ends. Beside the updated signals latched signals are also available in order to achieve stable signaling behavior and a permanent differential protection characteristic with reduced sensitivity when, for instance, intermittent faults have occurred. The updated signal as well as the stored signal are time-delayed in order to suppress any signaling caused by a transient event. On the other hand, instantaneous signals are used to block or restrain the differential protection functions as fast as possible:

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As soon as a CTS condition is detected (CTS: Idiff>(CTS)active is present), the function will raise the differential protection low set threshold to the DIFF: Idiff>(CTS) PSx setting; see Fig. 3-156.

The setting for this value determines the CTS operating mode:

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Signaling only:

DIFF: Idiff>(CTS) PSx = DIFF: Idiff> PSx. Differential protection remains unrestricted, but there is a risk of unwanted tripping occurring under load current.

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Restricted operation:

DIFF: Idiff>(CTS) PSx = maximum load current. This will permit the safe differential protection behavior, even during CT failure. There will be no unwanted trip under any load condition, but protection will remain operational for internal faults with currents exceeding the load current.

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Blocking:

DIFF: Idiff>(CTS) PSx = DIFF: Idiff>> PSx. In practice differential protection is blocked for all currents under normal operating conditions.