Technical data

2. Rate of change of frequency (ROCOF). The ROCOF values (positive
or negative) are compared to the trip settings and the inverter
ceases to energise the grid when the limits are violated.
• Residual current is monitored. The inverter ceases to energise the grid when:
- the cycle RMS value of the residual current violates the trip settings
for more than the duration of "clearance time"
- a sudden jump in the DC value of the residual current is detected.
• Earth-to-PV isolation resistance is monitored during start-up of the inverter. If
the value is too low, the inverter will wait 10 minutes and then make a new
attempt to energise the grid. Note: The value is corrected internally by an ad-
ditional 200 kΩ in order to compensate for measuring inaccuracy.
• If the inverter ceases to energise the grid due to grid frequency or grid volt-
age (not three-phase LoM), and if the frequency or voltage is restored within
a short time (short-interruption time), the inverter can reconnect when the
grid parameters have been within their limits for the specified time (reconnect
time). Otherwise, the inverter returns to the normal connection sequence.
3.3.4. Derating
Derating the output power is a means of protecting the inverter against overload and potential
failure. Furthermore, derating can also be activated to reduce the output power to the grid. De-
rating is activated by:
• PV over-current
• Internal over-temperature
• Excessive grid current
• Excessive grid voltage
• Excessive grid power
•
Grid over-frequency
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• External command for Power Level Adjustment (PLA feature)
• Excessive reactive power
1) Can only be activated when the inverter is connected to a medium/high-voltage AC network, e.g. the
grid code is selected as _MV country.
Derating is accomplished by adjusting the PV voltage and subsequently operating outside the
maximum power point of the PV arrays. The inverter continues to reduce the power until the
potential overload ceases or the commanded PLA level is reached. The total amount of time the
inverter has derated can be seen in the display [Log → Derating]. Security level-1 password pro-
vides access to view the distribution of the various types of derating.
Derating due to PV current or grid power indicates that too much PV power has been installed,
whereas derating due to grid current, grid voltage and grid frequency indicate issues with the
grid.
See the
Ancillary Services chapter for more information.
When derating on temperature the output power may oscillate by up to 1.5 kW.
Grid Voltage Derating
When the grid voltage exceeds a defined limit U1 , the inverter derates the output power. If the
grid voltage increases and exceeds the defined limit 10 min mean (U2) , the inverter ceases to
energise the grid, in order to maintain power quality and protect other equipment connected to
3. Description of the Inverter
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