44x/EN AP/Hb6
-108 MiCOM P40 Agile
P3070EN
ZL
IN> Fwd (B)
IN> Fwd (A)
A B
Figure 82: The DEF permissive scheme
The scheme has the same features/requirements as the corresponding distance scheme
and provides sensitive protection for high resistance earth faults.
Where “t” is shown in the diagram this signifies the time delay associated with an element,
noting that the time-delay for a permissive scheme aided trip would normally be set to zero.
4.8.3.2.2 Aided DEF Blocking Scheme
Figure 85 shows the element reaches, and Figure 86 the simplified scheme logic. The
signalling channel is keyed from operation of the reverse DEF element of the relay. If the
remote relay forward IN> element has picked up, then it will operate after the set time delay
if no block is received.
Figure 83: Independent channel – blocking scheme
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