ABB rec670 - Page 169

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 62: Fault time with maintained selectivity
The operation time can be set individually for each overcurrent protection.
To assure selectivity between different protection functions in the radial network, there
has to be a minimum time difference Dt between the time delays of two protections. To
determine the shortest possible time difference, the operation time of the protection, the
breaker opening time and the protection resetting time must be known. These time
delays can vary significantly between different protective 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 511 401-UUS A Section 8
Current protection
Bay control REC670 2.2 ANSI 163
Application manual