20 Program features
Combinatory limit
Combinatory limit monitors grid voltage and frequency simultaneously. There are limits for
the positive sequence and the negative sequence of grid voltage, and limits for
underfrequency and overfrequency.
The grid is declared as unstable, if
• the negative sequence voltage and the frequency are outside their limits, or
• the positive sequence voltage and the frequency are outside their limits.
If either of the conditions is true for the time defined by parameter 135.81 Combinatory trip
time, the grid is declared as unstable and the inverter disconnects from the grid.
Settings
Parameters:135.80 Combinatory trip,135.81 Combinatory trip time,135.84 Comb pos seq
voltage limit, 135.85 Comb neg seq voltage limit,135.86 Comb underfrequency limit,
135.87 Comb overfrequency limit
Rate of change of frequency
The grid frequency rate of change (RoCoF) has enable and limit parameters. If it is
enabled and the limits are exceeded, the inverter disconnects from the grid.
Settings
Parameters:135.110 Rate of change of freq enable,135.111 Rate of change of freq limit
Anti-islanding
The inverter Anti-islanding function prevents an island situation in an electrical grid. An
island in a grid is a situation in which a generator powers part of the grid even though the
power from the utility grid is cut off. Islanding can be dangerous to people working on the
grid and not realizing that the circuit is still powered. For that reason, distributed power
generators such as solar inverters can be required to detect an island situation and
immediately stop feeding power to the grid.
In a typical case when a part of the grid is islanded, the voltage and/or frequency of the
islanded part changes rapidly, and thus the island can be detected using voltage and/or
frequency limits. However, the worst-case scenario of an island situation is when the load
of the islanded grid part matches the energy production and this is when the limit based
voltage and/or frequency island detection method may fail. To also detect the worst-case
balanced load island situation, the active frequency shift based method can be used in the
inverter. The active method forces the voltage and/or frequency to rapidly change even in
the balanced load island situation. The island detection voltage and/or frequency limits will
then be exceeded causing the inverter to stop energy production.
The detection limits of the function can be configured using parameters which are preset
so that relevant grid-dependent requirements are fulfilled.
The Anti-islanding function can be enabled or disabled with parameter135.100 Anti-
islanding.
The inverter also supports an external transfer trip signal through SCADA or I/O.
Settings
Parameters:135.100...135.108
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