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 reli-
ably prevent false tripping.
Enhanced island detection method
KACO new energy's advanced islanding detection, uses a strategy to reliably detect islanding formation that is
based on the characteristic differences between an interconnected grid and an islanded grid, thus ensuring reli-
able fast detection and prevention of false tripping.
An interconnected grid is dominated by rotating machinery, as a consequence frequency is proportional to ac-
tive 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 in-
verter 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.
This detection method is combined with a two stage passive rate of change of frequency (ROCOF) observa-
tion.If the ROCOF of the grid exceeds the configured disconnection threshold of stage 1 for the configured dis-
connection time, the device switches to zero current mode. If the ROCOF of the grid exceeds the configured
disconnection threshold of stage 2 for the configured disconnection time, the device switches off. In case of an
island, this will shut down the island instantaneously. If the grid stabilizes, what might be the case if the ROCOF
event was due to a short disturbance in the power grid, the inverter will resume normal operation. With stage
1 active, the device has switched to zero current mode and will recommence feed-in after only 100 ms. With
stage 2 active, the device has switched off and the set reconnection conditions shall apply.
10 | Specifications
Manual
blueplanet gridsave 92.0 TL3-S blueplanet gridsave 110 TL3-S blueplanet gridsave 137 TL3-S
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