Grid Support Functions - Fronius GEN24 Operating Instructions Manual

Grid Support Functions

Voltage Fault In the event of faults in the grid, there is a risk of a large number of generation
Ride Through
plants being shut down unintentionally and thus a risk of network collapse. Grid
(VFRT) voltage disturbances (Voltage Fault, Gridvoltage-Disturbance) are short-term
voltage dips or surges in the grid. These voltage changes go beyond the normal
range of the operating voltage. However, the duration of the voltage changes is
short, so that the normal operating voltage is reached again before the system is
shut down (due to "Interface Protection"). Voltage Fault Ride Through means
that the inverter can ride through such a grid voltage fault without shutting down
prematurely. If the shutdown conditions of the protection settings ("Interface
Protection") are reached (time and value), the inverter always shuts down, thus
terminating VFRT operation. The requirements for the exact behaviour of the in-
verters during the fault depend on the respective grid connection rules. The fol-
lowing parameters determine this behaviour.
Classification into regions
The voltage fault detection of the inverter detects rapid mains voltage fluctu-
ations and classifies them into so-called regions according to the level of the
fault voltage (voltage level during the fault). Each region is assigned a specific
mains voltage value range. Three individual regions (R1, R2, R3) can be con-
figured. Each individual region has an adjustable detection threshold and several
parameters that determine the behaviour of the inverter within that region. The
detection limit is a relative voltage level and is specified in percent derived from
the AC nominal voltage. A value above 100 % means that the associated region
describes an overvoltage disturbance (High Voltage Ride Through HVRT). A value
less than 100 % means that the associated region describes an undervoltage
fault (Low Voltage Ride Through LVRT). Figure 1 shows an example of a typical
arrangement of the three regions (shown here with horizontal bars) by selective
choice of detection thresholds: R1 threshold 110 %, R2 threshold 90 %, R3
threshold 40 %. The voltage range between the limits of Region1 and Region2
(white bar) comprises the voltage range for normal operation (here: 90 to 110 %
of the nominal voltage). Region 1 comprises overvoltage disturbances, Region 2
consists of slight undervoltage disturbances (from 90 to 40 %). Region 3 consists
of severe undervoltage disturbances (below 40 %).
Division of the grid voltage range into three fault regions by selecting the detection thresholds.
IMPORTANT!
The length of the bars represents trip times for overvoltage and undervoltage
detection of the "Interface Protection" function group. This has no significance
for the VFRT functionality.
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