ABB RED650 - Permissive Under;Overreaching Scheme

IEC05000448 V1 EN-US
Figure 208: Simplified logic diagram for blocking scheme
13.4.6.2 Permissive under/overreaching scheme
M13922-17 v6
In the permissive scheme the forward directed earth-fault measuring element sends
a permissive signal to the other end, if an earth fault is detected in the forward
direction. The directional element at the other line end must wait for a permissive
signal before activating a trip signal. Independent channels must be available for
the communication in each direction.
An impedance measuring IED, which works in the same type of permissive mode,
with one channel in each direction, can share the channels with the communication
scheme for residual overcurrent protection. If the impedance measuring IED works
in the permissive overreaching mode, common channels can be used in single line
applications. In case of double lines connected to a common bus at both ends, use
common channels only if the ratio Z
1S
/Z
0S
(positive through zero-sequence source
impedance) is about equal at both ends. If the ratio is different, the impedance
measuring and the directional earth-fault current system of the healthy line may
detect a fault in different directions, which could result in unwanted tripping.
Common channels cannot be used when the weak-end infeed function is used in
the distance or earth-fault protection.
In case of an internal earth-fault, the forward directed measuring element operates
and sends a permissive signal to the remote end via the CS output (sent signal).
Local tripping is permitted when the forward direction measuring element operates
and a permissive signal is received via the CR binary input (received signal).
The permissive scheme can be of either underreaching or overreaching type. In the
underreaching alternative, an underreaching directional residual overcurrent
measurement element will be used as sending criterion of the permissive input
signal CSUR.
1MRK 505 394-UEN A Section 13
Scheme communication
Line differential protection RED650 2.2 IEC 421
Technical manual