ABB Relion 670 series, Technical Reference Manual

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13.6.1 Introduction
The Current reversal and weak-end infeed logic for residual overcurrent protection
ECRWPSCH (85) is a supplement to Scheme communication logic for residual
overcurrent protection ECPSCH (85).
To achieve fast fault clearing for all ground faults on the line, the directional ground-
fault protection function can be supported with logic that uses communication channels.
The 670 series IEDs have for this reason available additions to scheme communication
logic.
If parallel lines are connected to common busbars at both terminals, overreaching
permissive communication schemes can trip unselectively due to fault current reversal.
This unwanted tripping affects the healthy line when a fault is cleared on the other line.
This lack of security can result in a total loss of interconnection between the two buses.
To avoid this type of disturbance, a fault current reversal logic (transient blocking
logic) can be used.
Permissive communication schemes for residual overcurrent protection can basically
operate only when the protection in the remote IED can detect the fault. The detection
requires a sufficient minimum residual fault current, out from this IED. The fault
current can be too low due to an opened breaker or high-positive and/or zero-sequence
source impedance behind this IED. To overcome these conditions, weak-end infeed
(WEI) echo logic is used.
13.6.2 Principle of operation
13.6.2.1 Directional comparison logic function
The directional comparison function contains logic for blocking overreaching and
permissive overreaching schemes.
The circuits for the permissive overreaching scheme contain logic for current reversal
and weak-end infeed functions. These functions are not required for the blocking
overreaching scheme.
Use the independent or inverse time functions in the directional ground-fault protection
module to get back-up tripping in case the communication equipment malfunctions and
prevents operation of the directional comparison logic.
Figure 405 and figure 406 show the logic circuits.
Section 13
1MRK505222-UUS C
Scheme communication
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Technical reference manual