ABB RELION REX640 Technical Manual page 347

1MRS759142 C
REX640
Technical Manual
Parallel lines or transformers
When the lines are connected in parallel and if a fault occurs in one of the lines, it is
practical to have DPHxPDOC to detect the direction of the fault. Otherwise, there is
a risk that the fault situation in one part of the feeding system can de-energize the
whole system connected to the LV side.
GUID-9BF64A76-15A5-4559-96FA-1068B8EC1EA5 V1 EN
Figure 194: Overcurrent protection of parallel lines using directional protection
relays
DPHxPDOC can be used for parallel operating transformer applications. In these
applications, there is a possibility that the fault current can also be fed from the LV-
side up to the HV-side. Therefore, the transformer is also equipped with directional
overcurrent protection.
GUID-D664DE1E-DF2A-417D-9AC1-9180B7AFE811 V1 EN
Figure 195: Overcurrent protection of parallel operating transformers
Closed ring network topology
The closed ring network topology is used in applications where electricity distribution
for the consumers is secured during network fault situations. The power is fed at least
from two directions which means that the current direction can be varied. The time
Section 4
Protection functions
341