Experience with Measurement and Certification of Over Voltage Capability of Wind Turbine after Introduction of the new High Voltage Grid Code VDE 4120

Introduction

Overvoltage events can be caused by one or two phase faults in transmission lines. Other three-phase overvoltages can result from a transient change in the load of a transmission line, where the capacitive behavior abruptly becomes dominant (Ferranti effect).
This critical grid situation is not unknown to wind turbine manufacturers. Designing a wind turbine to stay online - as required by more and more grid codes - is very costly, considering that such grid situations are rather rare and measured against the overall life span of a wind turbine.
If grid operators opted for a more stable system they have to demand as well the OVRT (Over-Voltage-Ride-Through) capability. In order to ensure a fair market competition amongst manufacturers, test and certification procedures of the technical requirements should be defined clearly and be standardized. Experience out of the application of the new German technical test, validation and certification guideline (FGW TR3, TR4, TR8) will be shared.

Approach

WindGuard Certification is member of the working groups of the FGW and significantly involved in the development of standardized test and measurement procedures related to the certification of overvoltage capability. In Germany, the different steps are described in to 3 separate guidelines. The FGW TR3 describes the measurement procedures adapted to the German market, in the same way, the IEC 61400-21-1 aims for the international market.
The FGW TR4 describes the wind turbine computer model validation. The FGW TR8 is divided in two sections, the first section covering the type certification of single power generation units and the second, describing the certification of power generation plants. In Germany it is mandatory that these power generation plant certifications are based on certified power units.
New versions of all three guidelines were published on 1st March of 2016. Next revisions of these guidelines are expected at the end of the present year.


Main body of abstract

The FGW TR3 (measurement guideline) was adapted to the new requirements of the new grid code for high voltage connection VDE 4120 (mainly 110 kV). A new revision of FGW TR 3 is expected to be issued close to the announced new grid code VDE 4115 for medium voltage connection (mainly 7,5 kV until 35 kV). The differences between the actual TR3 and the published drafts of international guidelines will be discussed.
The FGW TR4 (model validation guideline) has been approximated to the IEC 61400-27, however, this guideline has to consider the special requirements of the new grid code.
The results of an electrical wind turbine capability evaluation according to TR3 and TR4 will be joined together in the unit or type certificate according to FGW TR8. The plant certification section of the FGW 8 provides standardized rules for the assessment of wind farms.
The chain of the connected guide lines will be feed by experience out of the praxis.


Conclusion

With the additions in the new FGW guidelines, it is now possible to approach the subject OVRT utilizing standardized procedures. Starting from the measurements of the behavior of the wind turbine during overvoltage, the corresponding adjustments of the model validation TR4 and by engaging in the unit or type certificates can now also be individually forecast the behavior of an overall wind farm.


Learning objectives
1. Main subjects of changings of the new guidelines of FGW TR 3, TR4 and TR 8
2. Share of Experience in Part of Measurement and Certification
3. Discussing of still open points by forecasting the behavior of wind turbines during overvoltage- ride-trough.