Advanced Islanding Detection - Kaco blueplanet 29.0TL3 Manual

10 | Specifications
10.4.2.1 Parameter for power ramp
Power ramp
1 2 3 4 4
Gradient
1 – 600 [% / min]
After every connect
After first connect
After grid error
10.5

Advanced islanding detection

Due to decentralized generation, there is the possibility that a deactivated part of the grid will remain live in an
unintended island due to the balance of load and generation in this part of the grid. The detection of uninten-
ded island formation is an important function of decentralized generating units and is related to the prevention
of damage to equipment as well as safety of personnel.
Depending on the structure and the operation of the distribution grid several dangers exist:
– In case of maintenance work in a distribution grid, personnel may be placed in danger if the deactivated
part of the grid remains live as an island. This is especially the case if not all safety rules are followed.
– If fast auto-reclosure is used in a distribution grid and the deactivated part of the grid remains live as an is-
land, reclosure will likely happen during phase displacement which might cause damage to rotating machi-
nery on the grid.
– In the event of a fault in a medium voltage grid, the faulty part of the grid is disconnected. If the fault has a
significant resistance, the deactivated part of a medium-voltage grid remains live as an island. Depending
on the type of fault, but explicitly in case of a fault in the transformer, dangerous medium voltage might be
accessible or even present in low-voltage appliances.
Especially for the last example very fast disconnection of the generating units to cause collapse of the forming
island is necessary. At the same time any island formation detection method may cause false tripping. The in-
dustry is therefore in constant research to develop methods that are fast and reliable and at the same time re-
liably prevent false tripping.
Enhanced island detection method
KACO new energy's advanced islanding detection uses a reliable islanding detection strategy based on the cha-
racteristic differences between an interconnected grid and an islanded grid, thus ensuring reliable fast detec-
tion and prevention of false tripping.
An interconnected grid is dominated by rotating machinery, as a consequence frequency is proportional to act-
ive power balance and voltage is proportional to reactive power balance. In contrast an islanded grid behaves
like a resonant circuit, as a consequence frequency is proportional to reactive power balance and voltage is
proportional to active power balance. The active enhanced island detection method detects this difference by
monitoring the behaviour of the grid. The enhanced island detection is monitoring the natural fluctuation of
the grid frequency and injects a minimal reactive power proportional to the rate of change of frequency. In the
moment an island is formed, the connected power grid closes a positive feedback loop which allows the inver-
ter to detect the changed situation and to disconnect. In case of formation of an island, the inverter discon-
nects within some 100 ms, well below 1000 ms.
– The number of parallel inverters does not affect the reliability of this function.
– This method also guarantees the minimisation of effects on the distribution grid.
– In normal operation no effects on harmonic content, flicker and grid stability are detected.
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AVISO: The power ramp allows a moderate increase of the
Performance possible.
Gradient of power limit. The maximum power limit increase to 100% of
nominal power with the gradient specified.
Soft start ramp up is activated for every connection of the inverter to
the grid.
Soft start ramp up is activated for the first connection of the inverter to
the grid on a particular day or after complete reboot of the inverter (AC
and DC disconnected)
Soft start ramp up is activated for connection of the inverter to the grid
after trip of the internal interface protection or via the external grid pro-
tection port (Powador-protect)
Manual
Kaco blueplanet 29.0TL3