ABB REL650 - Calculating Settings for Current Reversal and Weak-End Infeed Logic for Residual Overcurrent Protection ECRWPSCH (85)

Receive signal (CR)
Trip
Send signal (CS)
Step 1
Step 1 PUST1
Step 2
Step 2
Step 4 TRIP
Step 4 PUREV
Reverse:
PUST2
TRIP
TRIP
OR
AND
EF4PTOC (51N_67N)
ANSI11000080_1_en.vsd
ANSI11000080 V1 EN
Figure 30: Logic for four step residual overcurrent protection blocking
communication scheme
The trip signal from step 2 must be delayed so that the blocking signal has enough time for
blocking at external faults.
3.1.12 Calculating settings for current reversal and weak-end infeed
logic for residual overcurrent protection ECRWPSCH (85)
The four step residual overcurrent protection can only operate if the fault current to the fed
to the protection is larger than about 3% of the rated current (settable). There is a risk that
the fault current infeed from one of the line ends is very small, but not zero. In such case
the following can be the consequence of a short circuit close to the line end with small fault
current infeed.
1MRK 506 334-UUS A Section 3
REL650 setting examples
79
Application manual