Functions
2.3 Directional Overcurrent Protection 67, 67N
SIPROTEC, 7SJ62/64, Manual
C53000-G1140-C207-2, Release date 01.2008
97
For line sections supplied from two sources or in ring-operated lines, the overcurrent protection has to be sup-
plemented by the directional criterion. Figure 2-21 shows a ring system where both energy sources are merged
to one single source.
Figure 2-21 Transmission lines with sources at both ends
Depending on the setting of parameter 613 50N/51N/67N w., the ground current element can operate either
with measured values I
N
or with the values 3I0 calculated from the three phase currents. Devices featuring a
sensitive ground current input, however, use the calculated quantity 3I0.
For each element the time can be blocked via binary input or automatic reclosing (cycle-dependent), thus sup-
pressing the trip command. Removal of blocking during pickup will restart time delays. The Manual Close signal
is an exception. If a circuit breaker is manually closed onto a fault, it can be re-opened immediately. For over-
current elements or high-set elements the delay may be bypassed via a Manual Close pulse, thus resulting in
high-speed tripping.
Furthermore, immediate tripping may be initiated in conjunction with the automatic reclosing function (cycle de-
pendant).
Pickup stabilization for the 67/67N elements of the directional overcurrent protection can be accomplished by
means of settable dropout times. This protection comes into use in systems where intermittent faults occur.
Combined with electromechanical relays, it allows different dropout responses to be adjusted and a time
grading of digital and electromechanical relays to be implemented.
Pickup and delay settings may be quickly adjusted to system requirements via dynamic setting swapping (see
Section 2.4).
Utilizing the inrush restraint feature tripping may be blocked by the 67-1, 67-TOC, 67N-1, and 67N-TOC ele-
ments in phases and ground path when inrush current is detected.
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