GUID-BF32C1D4-ECB5-4E96-A27A-05C637D32C86 V1 EN
Figure 95: Examples of network rotating direction
4.1.3.7 Application
DPHxPDOC is used as short-circuit protection in three-phase distribution or sub
transmission networks operating at 50 or 60 Hz.
In radial networks, phase overcurrent IEDs are often sufficient for the short circuit
protection of lines, transformers and other equipment. The current-time
characteristic should be chosen according to the common practice in the network. It
is recommended to use the same current-time characteristic for all overcurrent
IEDs in the network. This includes the overcurrent protection of transformers and
other equipment.
The phase overcurrent protection can also be used in closed ring systems as short
circuit protection. Because the setting of a phase overcurrent protection system in
closed ring networks can be complicated, a large number of fault current
calculations are needed. There are situations with no possibility to have the
selectivity with a protection system based on overcurrent IEDs in a closed ring system.
In some applications, the possibility of obtaining the selectivity can be improved
significantly if DPHxPDOC is used. This can also be done in the closed ring
networks and radial networks with the generation connected to the remote in the
system thus giving fault current infeed in reverse direction. Directional overcurrent
IEDs are also used to have a selective protection scheme, for example in case of
parallel distribution lines or power transformers fed by the same single source. In
ring connected supply feeders between substations or feeders with two feeding
sources, DPHxPDOC is also used.
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,
1YHT530004D05 D Section 4
Protection functions
615 series 191
Technical Manual
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