Kaco blueplanet gridsave 92.0 TL3-S Manual page 82

10 | Specifications
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
improved islanding detection monitors the natural fluctuation of the grid frequency and feeds in a minimal reactive
power that is proportional to the rate of change of the frequency. At the moment that islanding is established, the con-
nected grid closes a positive feedback loop, which allows the inverter to detect the altered situation and 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 guarantees that the impact on the distribution grid is minimised.
– 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 disconnection threshold (stage 2)
for the configured disconnection time, the device switches off. In case of an island, this will shut down the island instant-
aneously. 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 100 ms. With stage 2 active, the device has switched off and the set reconnection con-
ditions shall apply.
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