DEF IDMT
DEF Bu2
DEF Bu1
DEF Inst
Trip
A
Trip
B
LD0V
DEF-Reverse
CB Open
DEF IDMT
DEF Bu2
DEF Bu1
DEF Inst
LD0V
CB Open
E03518
DEF Forward
ZL
DEF Forward
DEF-Reverse
DEF-Forward
DEF-Forward
CRx
CTx
CRx
CTx
Selectable features
A
B
&
&
&
&
1
1
1
1
&
&
&
&
t
IDMT
t
Bu2
t
Bu1
t
IDMT
t
Bu2
t
Bu1
Figure 115: Aided DEF POR scheme
5.6
AIDED DEF BLOCKING SCHEME
The scheme has the same features/requirements as the corresponding Distance scheme and provides sensitive
protection for high resistance earth faults.
The signalling channel is keyed from operation of the reverse Aided DEF element (DEF REV Set). If the remote
device’s forward Aided DEF element (DEF FWD Set) has picked up, it operates after the Aid. 1 DEF Dly. expires if no
block is received.
Where ‘t’ is shown in the diagram this signifies the time delay associated with an element. To allow time for a
blocking signal to arrive, a short time delay on aided tripping must be used.
The logic is:
● Send logic: Key channel if DEF REV Set picks up
● Trip logic: Trip if DEF FWD Set AND Channel NOT Received, after Aid. 1 DEF Dly. expires.
Chapter 8 - Carrier Aided Schemes P543i/P545i
232 P54x1i-TM-EN-1
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