Alstom MiCOM P546 - 1.23.12 Delta scheme POR - permissive overreach transfer trip (Distance option only)

P54x/EN OP/La4 Operation
(OP) 5-72 MiCOM P543, P544, P545 & P546
OP
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. To
allow time for a blocking signal to arrive, a short time delay on aided tripping must be used.
CRx
CRx
CTx
CTx
DEF-R
t
Bu1
1
Trip
A
1
Trip
B
&
DEF-F
DEF Inst
DEF Bu1
DEF Bu2
DEF IDMT
t
Bu2
t
IDMT
t
Bu1
t
Bu2
t
IDMT
DEF-F
DEF Inst
DEF Bu1
DEF Bu2
DEF IDMT
DEF-R
&
Stop
Start
Stop
Start
P1155ENa
P1134ENa
Figure 47 Aided DEF (ground) blocking scheme logic (Distance option only)
1.23.12 Delta scheme POR - permissive overreach transfer trip (Distance option only)
The ch
annel for a directional comparison POR scheme is keyed by operation of the
overreaching Delta Forward elements of the relay. If the remote relay has also detected a
forward fault upon receipt of this signal, the relay will operate. Listed below are some of the
main features/requirements for a permissive overreaching scheme:
 Permissive overreach schemes tend to be more secure than blocking schemes because
forward directional decisions must be made at both ends of the line before tripping is
allowed. Failure of the signaling channel will not result in unwanted tripping.
 If the infeed source at either end of the line is weak, the POR scheme must be
supplemented with Weak Infeed logic.
 The scheme requires a duplex signaling channel to prevent possible relay maloperation
due to spurious keying of the signaling equipment. This is necessary due to the fact that
the signaling channel is keyed for faults external to the protected line.
 Current reversal guard logic is used to prevent healthy line protection maloperation for
the high speed current reversals experienced in double circuit lines, caused by
sequential opening of circuit breakers.
 If the signaling channel fails, Basic distance scheme tripping will be available.
This scheme is similar to that used in the LFDC relay, and is shown in Figure 48.
Send
logic:  Fault Forward
Permissive trip logic:  Fault Forward plus Channel Received.