GUID-BF32C1D4-ECB5-4E96-A27A-05C637D32C86 V1 EN
Figure 111: Examples of network rotation direction
4.1.4.7 Application
DPH3xPDOC is used as short circuit protection in three-phase distribution or sub
transmission networks operating at 50 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 DPH3xPDOC 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 the 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. DPH3xPDOC is also used in the ring-connected supply feeders between
substations or feeders with two feeding sources.
Parallel lines or transformers
When the lines are connected in parallel and a fault occurs in one of the lines, it is
practical to have DPH3xPDOC to detect the direction of the fault. Otherwise, there
1YHT530004D05 D Section 4
Protection functions
615 series 217
Technical Manual
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