Example 1 - ABB RELION 670 Series Applications Manual

1MRK 505 337-UUS A
IEC05000204 V1 EN-US
Figure 83: 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:
protection resetting
time:
Breaker opening time:
Example
Assume two substations A and B directly connected to each other via one line, as shown in the
figure below. We study a fault located at another line from the station B. The fault current to the
overcurrent protection of IED B1 has a magnitude so that the protection will have instantaneous
function. The overcurrent protection of IED A1 must have a delayed function. The sequence of
events during the fault can be described using a time axis, see figure 84.
Application manual
15-60 ms
15-60 ms
20-120 ms
Current protection
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Section 7
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