Functions
2.3 Directional Overcurrent Protection 67, 67N
SIPROTEC, 7SJ62/64, Manual
C53000-G1140-C207-2, Release date 01.2008
96
2.3 Directional Overcurrent Protection 67, 67N
With directional overcurrent protection the phase current and the ground currents are each provided with three
elements. All elements may be configured independently from each other and combined as desired.
High-set current elements 67-2 and overcurrent element 67-1 always operate with a definite tripping time, the
third element 67-TOC operates with an inverse tripping time.
Applications
• The directional overcurrent protection allows the application of multifunctional protection devices 7SJ62/64
also in systems where protection coordination depends on knowing both the magnitude of the fault current
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 directional criterion.
2.3.1 General
For parallel lines or transformers supplied from a single source (Figure 2-20), 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 2-20), 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 2-20.
Figure 2-20 Overcurrent protection for parallel transformers
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