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2.3
Directional Overcurrent Protection 67, 67N
Directional overcurrent protection includes two elements each for the phase currents and the ground current.
All elements operate with a definite tripping time, they are independent of each other and can be combined as
desired.
Applications
• The directional overcurrent protection allows the application of Feeder Automation Controller 7SC80 also in
systems where selectivity depends on both the overcurrent criterion and the direction of power flow to the
fault location.
• The non-directional overcurrent protection described in Section 2.2 may operate as overlapping backup pro-
tection or may be disabled. Additionally, individual elements (e.g. 67-2 and/or 67N-2) may be interconnected
with the directional overcurrent protection.
• For parallel lines or transformers supplied from a single source, only directional overcurrent protection allows
selective fault detection.
• For line sections supplied from two sources or in ring-operated lines, the overcurrent protection has to be
supplemented by the element-specific directional criterion.
2.3.1
General
For parallel lines or transformers supplied from a single source (Figure 2-11), the second feeder (II) is opened
on occurrence of a fault in the first feeder (I) if tripping of the breaker in the parallel feeder is not prevented by
a directional measuring element (at B). Therefore, where indicated with an arrow (Figure 2-11), directional over-
current protection is applied. Please ensure that the "forward" direction of the protection element is in the di-
rection of the line (or object to be protected). This is not necessarily identical with the direction of the normal
load flow, as shown in Figure 2-11.
Figure 2-11
Overcurrent protection for parallel transformers
SIPROTEC, 7SC80, Manual
E50417-G1140-C486-A1, Release date 12.2011
2.3 Directional Overcurrent Protection 67, 67N
Functions
71
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