ABB Relion 650 Series Technical Manual page 708

Section 19
Inverse time characteristics
702
Time
IEC05000131 V1 EN-US
Figure 322: 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.
1MRK 511 424-UEN B
Fault point
position
en05000131.vsd
Bay control REC650 2.2 IEC
Technical manual