ABB RELION 670 SERIES Applications Manual page 508

Section 9
Current protection
502
10
tfunc1
n
tfunc2 n
0.01
10
IEC05000204 V2 EN
Figure 258: 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 15-60 ms
time:
Protection resetting time: 15-60 ms
Breaker opening time: 20-120 ms
Time-current curves
Str
n
Fault Current
Line distance protection REL670 2.2 ANSI
1MRK 506 369-UUS -
10000
en05000204.ai
Application manual