Functions
2.3 Directional Overcurrent Protection Ground 67, 67N
SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A5, Release date 11.2012
93
Figure 2-23 Logic diagram of the directional inverse-time overcurrent element 67N-TOC
2.3.5 Interaction with Fuse Failure Monitor (FFM)
Spurious tripping can be caused by a measuring voltage failure due to a short circuit or phase failure in the
voltage transformer secondary system or pickup of the voltage transformer mcb (fuse). In the event of a single-
phase or two-phase failure of the measuring voltage, it is possible to recognize this condition and block the di-
rectional overcurrent time protection elements (ground), see logic diagrams. In such a case, the undervoltage
protection and the sensitive ground fault detection will also be blocked.
For additional information on the operation of the fuse failure monitor, see section 2.10.1 Measured Value Su-
pervision.
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