Advanced Islanding Detection - Kaco blueplanet 92.0 TL3 US Manual

Manual
10.4.3.1 Parameters for power gradient in normal operation
Country- Men Display/
spec. Set- u Setting
tings level
Operation Mode
On / Off
Increasing gradient
1-65534 [% S
min]
Decreasing gradient
1 – 65534 [% S
min]
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 unin-
tended island due to the balance of load and generation in this part of the grid. The detection of unintended island forma-
tion 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 island, reclo-
sure will likely happen during phase displacement which might cause damage to rotating machinery 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 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
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 reliable fast detection
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 an island is formed, the connected power grid
closes a positive feedback loop which allows the inverter to detect the changed situation and to disconnect. In case of for-
mation 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 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) observation.If the RO-
COF of the grid exceeds the configured disconnection threshold of stage 1 for the configured disconnection time, the de-
vice 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 instanta-
neously. If the grid stabilizes, what might be the case if the ROCOF event was due to a short disturbance in the power
KACO blueplanet 92.0 TL3 US KACO blueplanet 110 TL3 US KACO blueplanet 125 TL3 US
Action in this menu/meaning
Activate or disable the power gradient limtitation in normal operation.
The change in the active power is limited to a configured power increase
gradient.
/
max
The change in the active power is limited to a configured power de-
crease gradient.
/
max
Specifications | 10
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