Voltage-Time Monitoring; Frequency-Time Monitoring - Siemens SINAMICS S120 System Manual

Function modules
5.3 Description of the function modules
Function
As the grid control is missing, generally the creation of an island grid quickly results in
violation of the frequency and voltage limit values. As a consequence, it is detected by the
frequency and voltage monitoring function. However, if the power generated by the power
generating system and the power used in the remaining island grid are the same, then
frequency and voltage remain within the limit values and the creation of an island grid is
either not detected at all – or not quickly enough.
For cases such as these, an active anti-islanding function is required such as the "Grid
monitoring anti-islanding" of the Active Line Module. It operates according to the frequency
shift technique, i.e. if the function is activated, then the Active Line Module attempts to
continually actively change the line frequency. However, this can only occur in an island grid,
i.e. the creation of an island grid is always reliably and quickly detected.
Note
During a grid short-circuit (r5502.4 = 1), the active anti-islanding function is inhibited, so that
this grid fault can be ridden through and the supporting reactive current injected.
However, if it is necessary to satisfy requirements regarding shutting down the formation of
an island grid, the subsequently described voltage-time monitoring can be employed, for
example.
5.3.3.3

Voltage-time monitoring

The voltage-time monitoring provides two characteristics with 10 adjustable interpolation
points to set the time and the associated voltage value.
One characteristic is used to monitor the voltage increase (HVRT, high voltage ride through),
the other characteristic is used to monitor the voltage dip (LVRT: low voltage ride through).
Status bits and messages are used to signal if the defined tolerance range is violated for the
line voltage characteristic.
This means that the grid voltage can be monitored, and after a grid fault, a response that
complies with the power utility company initiated.
5.3.3.4

Frequency-time monitoring

The frequency-time monitoring provides two characteristics with 10 adjustable interpolation
points to set the time and the associated frequency value.
One characteristic is used to monitor the frequency increase (HFRT, high frequency ride
through), the other characteristic is used to monitor the frequency decrease (LFRT, low
frequency ride through).
Status bits and messages are used to signal if the defined tolerance range is violated for the
line voltage characteristic.
This means that the grid frequency can be monitored, and after a grid fault, a response that
complies with the power utility company's grid codes initiated.
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System Manual, 04/2015, A5E03347436A
Grid infeed