– 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 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
Die erweiterte Inselnetzerkennung von KACO new energy, verwendet eine Strategie zur zuverlässigen
Erkennung der Inselbildung, die auf den unterschiedlichen Eigenschaften eines Verbundnetzes und
eines Inselnetzes basiert und somit eine zuverlässige schnelle Erkennung und Vermeidung von
Fehlauslösungen gewährleistet.
An interconnected grid is dominated by rotating machinery, as a consequence frequency is propor-
tional to active power balance and voltage is proportional to reactive power balance. In contrast an is-
landed 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 detec-
tion method detects this difference by monitoring the behaviour of the grid. The enhanced island de-
tection 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 situ-
ation and to disconnect. In case of formation of an island, the inverter disconnects within some 100
ms, well below 1000 ms.
– The number of parallel inverters does not affect the reliability of this function.
– This method also ensures that the impact on the distribution grid is kept to a minimum.
– 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) ob-
servation. If the ROCOF 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 ex-
ceeds 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 inverter
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 recon-
nection conditions apply.
Manual Specifications | 10
KACO blueplanet 87.0 TL3 KACO blueplanet 92.0 TL3 KACO blueplanet 105 TL3 KACO blueplanet 110 TL3
KACO blueplanet 125 TL3 KACO blueplanet 137 TL3 KACO blueplanet 150 TL3 KACO blueplanet 155 TL3 KACO
blueplanet 165 TL3
Page 93
EN-US
To Next Page
Loading...
Need help?
General