ABB REL650 Applications Manual page 77

1MRK 506 334-UUS A
Application manual
The four step residual overcurrent protection has the following purpose:
• Fast and sensitive protection for ground-faults on the protected line.
• Backup protection for ground-faults on the adjacent busbar in case the distance
protection is unavailable (after fuse failure blocking)
• Sensitive detection of high resistive ground-faults and series faults on the protected
line.
The reach of four step residual overcurrent protection depends on the operation state and
the fault type. Therefore the setting must be based on fault calculations made for different
faults, fault points and switching states in the network. Although it is possible to make
hand calculations of different faults, the use of computer based fault calculations is
recommended. The time delay characteristic has to be adopted to the praxis used in the
network.
The following principle for the four step residual phase overcurrent protection is
proposed:
• Step 1 (3I >>>) with high current setting and zero delay. Step 1 has directional
0
function with the residual voltage as directional reference. This step gives a fast trip
for the line ground-faults approximately 70 % out on the line.
• Step 2 (3I >>) with a current setting that enables detection of all short circuits with
0
zero sequence current. Step 2 has directional function with the residual voltage as
directional reference. The function has a short delay to enable selectivity.
• Step 4 (3I >) with a current setting that enables detection of high resistive ground-
0
faults and series faults on the protected line. Step 4 has non-directional function. The
function has a longer delay to enable selectivity.
Step 2- reach
Step 1- reach
A
REL 650
Y
ANSI11000115 V2 EN
Figure 22: Residual overcurrent protection combined with communication scheme
REL650 setting examples
B
Z 1 = R 1 + jX 1
Z 0 = R 0 + jX0
Communication
REL 650
Step 1- reach
Step 2- reach
Section 3
C
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ANSI11000115_2_en.vsd
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