Time-current curves
Fault Current
10
10
0.01
10000
en05000204.ai
Str
tfunc1
n
n
tfunc2
Trip time
n
IEC05000204 V2 EN-US
Figure 93: Fault time with maintained selectivity
The operation time can be set individually for each overcurrent protection. To assure
selectivity between different protective protections, in the radial network, there have to
be a minimum time difference Dt between the time delays of two protections. The
minimum time difference can be determined for different cases. To determine the
shortest possible time difference between we must have knowledge about operation
time of protections, breaker opening time and protection resetting time. These time
delays can vary significantly between different pieces of equipment. The following
time delays can be estimated:
protection operation
time:
15-60 ms
protection resetting time: 15-60 ms
Breaker opening time: 20-120 ms
1MRK 505 370-UUS A Section 7
Current protection
Busbar protection REB670 2.2 ANSI 195
Application manual
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