ABB REL650 Applications Manual page 402

Section 12
Scheme communication
396
gives instantaneous trip of the protected object. The overreaching zone used in the
teleprotection scheme must be activated at the same time as the received signal is present.
The scheme can be used for all line lengths.
In permissive overreaching schemes, the communication channel plays an essential roll to
obtain fast tripping at both ends. Failure of the communication channel may affect the
selectivity and delay tripping at one end at least, for faults anywhere along the protected
circuit.
Teleprotection operating in permissive overreaching scheme must beside the general
requirement of fast and secure operation also consider requirement on dependability.
Inadequate security can cause unwanted tripping for external faults. Inadequate speed or
dependability can cause delayed tripping for internal faults or even unwanted operations.
At the permissive overreaching scheme, the send signal (CS) might be issued in parallel
both from an overreaching zone and an underreaching, independent tripping zone. The CS
signal from the overreaching zone must not be prolonged while the CS signal from zone
1 can be prolonged.
There is no need to delay the trip at receipt of the signal, so set the timer tCoord to zero.
A
OR
B
CS
OR
A
A
IEC09000014 V1 EN
Figure 194: Principle of Permissive overreaching scheme
OR: Overreaching
CR: Communication signal received
CS: Communication signal send
T2: Timer step 2
Unblocking scheme
Metallic communication paths adversely affected by fault generated noise may not be
suitable for conventional permissive schemes that rely on signal transmitted during a
1MRK 506 334-UUS A
B
TRIP = OR + CR OR + T2
B B B , B
IEC09000014-1-en.vsd
Application manual
OR
A