Planning the electrical installation 59
FIMER recommends that the transformer is equipped with an off-load tap changer for
voltage regulation on the high-voltage side of the winding with two 2.5% step points to the
plus and minus directions.
The inverter does not require a specific transformer notation. FIMER recommends using
traditional notations, such as Dy11d0.
The AC side of the inverter is designed only for IT (floating) networks, do not ground the
neutral (star) point of the transformer on the inverter side or connect it to the neutral points
of other windings.
Grounded Y or Delta high-voltage side configurations may require additional plant-level
protection for phase loss detection.
Selecting the grid disconnecting device
As standard, the inverter is equipped with AC contactors to disconnect from the grid.
These do not provide total electrical isolation with lockable and visible status indication.
Additionally, as an option, the inverter can be equipped with hand-operated grid
disconnecting devices (disconnectors) or AC breakers (one per power section), which
isolate the inverter and the solar generator from the electrical power system. Even with
these optional internal isolation devices, the AC busbars or internal auxiliary transformers
are not isolated from the electrical power system. Before you do installation and
maintenance work on the inverter, always isolate the AC cables and busbars from the
electrical power system with an AC disconnector outside the inverter, for example, a
breaker on the HV side of the transformer.
Refer to Ratings on page 94 and AC output connection specification on page 102 for the
correct current and voltage dimensioning. If you do not know the installation-specific short-
circuit current of the grid, use the value in AC output connection specification on page 102
for adequate short-circuit current capability of the grid disconnecting device. The grid
disconnecting devices must be lockable.
Selecting the DC input disconnecting device
As standard, the inverter is equipped with DC contactors. These do not provide total
electrical isolation with lockable and visible status indication, they provide only
disconnection from the panels. As an option, hand-operated DC disconnecting devices
(one per power section) are available for isolation. These DC disconnecting devices do not
isolate the DC fuses, conductors or terminals of the inverter from the voltage. Hence the
DC side must have breakers or other suitable disconnection means for the isolation
between the PV generator and inverter, for example, a separate disconnector box.
Refer to Ratings on page 94 and DC input connection data on page 104 for the correct
current and voltage dimensioning. If you do not know the installation-specific short-circuit
value for each DC input disconnecting device, refer to DC input connection data on page
104 for adequate short-circuit current capability of the DC input disconnecting devices.
Make sure that the DC-side disconnecting devices can handle the backfeed current. The
DC input disconnecting devices must be lockable.
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