ABB RELION REX640 Technical Manual page 360

Protection functions
Figure 217: 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.
Figure 218: 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 grading between the network level stages is challenging
without unnecessary delays in the time settings. In this case, it is practical to
use the directional overcurrent protection relays to achieve a selective protection
scheme. Directional overcurrent functions can be used in closed ring applications.
The arrows define the operating direction of the directional functionality. The
double arrows define the non-directional functionality where faults can be detected
in both directions.
360
1MRS759142 F
REX640
Technical Manual