Weak-end infeed logic
Figure 298 shows a typical system condition that can result in a missing operation.
Note that there is no fault current from node B. This causes that the IED at B cannot
detect the fault and trip the breaker in B. To cope with this situation, a selectable weak-
end infeed logic is provided for the permissive overreaching scheme.
en99000054_ansi.vsd
LINE 1
A B
Strong
source
Weak
source
CLOSEDCLOSED
FAULT
ANSI99000054 V1 EN
Figure 298: Initial condition
3.13.2.2 Setting guidelines
The parameters for the current reversal and weak-end infeed logic for residual
overcurrent protection function are set via the local HMI or PCM600.
Current reversal
The current reversal function is set on or off by setting the parameter CurrRev to
Enabled or Disabled. Time delays shall be set for the timers tPickUpRev and
tDelayRev.
tPickUpRev is chosen shorter (<80%) than the breaker opening time, but minimum 20
ms.
tDelayRev is chosen at a minimum to the sum of protection reset time and the
communication reset time. A minimum tDelayRev setting of 40 ms is recommended.
The reset time of the directional residual overcurrent protection (EF4PTOC) is
typically 25 ms. If other type of residual overcurrent protection is used in the remote
line end, its reset time should be used.
The signal propagation time is in the range 3 – 10 ms/km for most types of
communication media. In communication networks small additional time delays are
added in multiplexers and repeaters. Theses delays are less than 1 ms per process. It is
often stated that the total propagation time is less than 5 ms.
When a signal arrives or ends there is a decision time to be added. This decision time is
highly dependent on the interface between communication and protection used. In
many cases external interface (teleprotection equipment) is used. This equipment
makes a decision and gives a binary signal to the protection device. In case of analog
1MRK504116-UUS C Section 3
IED application
733
Application manual
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