en05000131.vsd
Time
Fault point
position
IEC05000131 V1 EN-US
Figure 409: Inverse time overcurrent characteristics with inst. function
The inverse time characteristic makes it possible to minimize the fault clearance
time and still assure the selectivity between protections.
To assure selectivity between protections there must be a time margin between the
operation time of the protections. This required time margin is dependent of
following factors, in a simple case with two protections in series:
• Difference between pickup time of the protections to be co-ordinated
• Opening time of the breaker closest to the studied fault
• Reset times of the protections
• Margin dependent of the time delay inaccuracy of the protections
Assume we have the following network case.
Section 25 1MRK 505 394-UEN A
Inverse time characteristics
870 Line differential protection RED650 2.2 IEC
Technical manual
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