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3-38
Protection Functions
The operation delay setting is 0.14 s = 7x20 ms.
The upper start and trip status lines are for a
case with the intermittent time set to zero.
No trip will happen.
The lower start and trip status lines show another
case with intermittent time setting 0.12 s. In this
case a trip signal will be issued at t=0.87 s.
857-UM001A-EN-P – July 2009
The fourth and the next faults do occur after release time but within
release time + intermittent time. Thus the operation delay counter is
advanced at every fault in the case the intermittent time setting is
more than 100 ms (the lower status lines in the figure) and finally a
trip signal is issued at t=0.87 s.
When faults do occur more than 20 ms apart each other, every single
fault will increment the operation delay counter by 20 ms. In this
example the actual operation time starting from the third fault will be
617 ms although, the setting was 140 ms. In case the intermittent
setting would have been 0.2 s or more, the two first faults had been
included and a trip would have issued at t=0.64 s.
Figure 3.21 – Effect of the intermittent time parameter
Setting groups
There are two settings groups available. Switching between setting
groups can be controlled by digital inputs, virtual inputs (mimic
display, communication, logic) and manually.
Figure 3.22 – Block diagram of the directional intermittent transient earth fault stage I
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0T
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