Functions
6-257SJ63 Manual
C53000-G1140-C120-1
6.2.1.3 Reverse Interlocking Bus Protection
Application Exam-
ple
The pickup of a time-overcurrent relay element may be blocked via binary inputs. At
the users option, the binary inputs can be set up to block tripping when DC voltage is
applied or when DC voltage is removed. Reverse interlocking allows for faster protec-
tion by eliminating the need for time-current coordination. Reverse interlocking is often
used, for example, at generating stations in applications where a station supply trans-
former supplied from the transmission grid serves internal loads of the generation sta-
tion via a medium voltage bus with multiple feeders (see Figure 6-14).
When the 7SJ63 relay is used as the source-side relay in a reverse interlocking
scheme, a short time delay must be set for the 50-2 element so that a load-side relay
has the chance to block tripping (Figure 6-14). The load-side relay should pickup im-
mediately for down-line faults so that a blocking signal is immediately sent to the
source-side relay’s binary inputs. The load-side protective device can then initiate a
time delayed trip, as long as the time delay is less than the time delay settings of the
source-side relay’s 50-1 and 50N-1 relay elements and the time multiplier settings of
the source-side relay’s 51 and 51N relay element. The source side relay’s 50-1, 50N-
1, 51 and 51N relay elements will provide redundant protection against faults in the
load side relay’s zone of protection since their associated time delay settings are
greater than the load side relay’s time delay setting.
Pickup messages generated by the load-side relay are passed to a binary input of the
source-side relay as input message “!EORFN”.
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