U
B
U
C
U
A
U
C
U
B
U
A
NETWORK ROTATION ABC
NETWORK ROTATION ACB
U
BC
U
AB
U
CA
U
BC
U
CA
U
AB
I
A
I
B
I
C
I
A
I
B
I
C
Figure 160: Examples of network rotating 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
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.
1MRS757644 H
Protection functions
620 series
Technical Manual
315