Island Grid - Siemens SINAMICS S120 System Manual

3.2

Island grid

An island grid supplies a limited area and has no connection to the public grid or to other
grids. The utility company operating the grid must maintain the balance between used and
generated power in the island grid; an energy storage system can be used.
The company operating an island grid can define their own grid codes. These can deviate
from the regulations of public grid operators (power utility companies).
Figure 3-2
Requirements placed on distributed power producers
● Black start of the island grid
This function involves establishing an island grid voltage starting from zero with the
disconnector open to the external grid.
Generally, a component black start is required (24 V DC supply).
● Controlling the grid voltage and frequency, and quickly adapting the generated power to
the varying load conditions
● Provision of the entire short-circuit current in the event of a short-circuit
● Provision of reactive power for grid support
● Reestablishing the voltage and maintaining the frequency after the short-circuit has been
cleared
Requirements placed on a higher-level island grid control
● Matching the generated power (active power/reactive power) at the rated frequency to the
load power (active power/reactive power)
Using an isolating transformer
● An isolating transformer with neutral point on the island grid side must be used if a neutral
conductor is required in the island grid.
● An isolating transformer must also be used in order to avoid inadmissible ground
currents, which can occur as a result of clocked (PWM) frequency converters connected
to the power generating unit.
Function modules for an island grid
Additional software functions are required for operation in an island grid. These are defined
in function modules, and must be explicitly activated.
The following function modules of the Active Line Module are required for operation in an
island grid:
● Line transformer function module (Page 34)
● Function module for grid droop control (Page 35)
Grid infeed
System Manual, 04/2015, A5E03347436A
Schematic representation of an island grid
Grid types
3.2 Island grid
23