Kaco blueplanet 87.0 TL3 Manual page 89

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 industry is therefore in
constant research to develop methods that are fast and reliable and at the same time reliably prevent false tripping.
Enhanced island detection method
The enhanced island detection of KACO new energy, employs a strategy to reliably detect island formation that is based
on the characteristic 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 active 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 bal-
ance. 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 of formation of an island the connected power
systems is closing a positive feedback loop what allows the inverter to detect the changed situation and to disconnect. In
case of formation of an island, the inverter disconnects within some 100 ms, well below 1000 ms.
ž The number of parallel inverters does not affect the reliability of this function.
ž This method also ensures that the impact on the distribution grid is kept to a minimum.
ž 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) observation. If the RO-
COF of the grid exceeds the configured disconnection threshold (stage 1) for the configured disconnection time, the
device switches to zero current mode. If the ROCOF of the grid exceeds the configured shutdown threshold (stage 2) for
the configured shutdown time, the device shuts down. 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 in-
verter will resume normal operation. In the event of active stage 1, the device switches to zero current mode, and re-
starts the infeed after a few 100ms. At stage 2, the device has shut down and the set reconnection conditions apply.
KACO blueplanet 87.0 TL3 KACO blueplanet 92.0 TL3 KACO blueplanet 110 TL3 KACO blueplanet 125 TL3
KACO blueplanet 137 TL3 KACO blueplanet 150 TL3
Page 89