Overall approach of the harmonic issues in offshore windfarms

Antoni Dalmau Pons, Albert Van Ranst
Tractebel Engineering SA, Brussels, Belgium


This paper is intended to provide guidance to wind project developers and grid connection EPC contractors in dealing with harmonic issues in offshore wind power plants. Assumptions and calculations to be performed for a correct harmonic assessment are discussed, together with the timing of such assessment in the project schedule.

Harmonic calculations are separated in three main categories: harmonic emissions at the grid connection point, background harmonic amplification and windfarm grid immunity. The results may show a need for mitigating measures.

The approach is based on a windfarm harmonic model and on harmonic equivalent of upstream grid. Due to tight schedule in windfarm development, WTG harmonic equivalents and grid harmonic equivalent are often provided during phases in where platform design has already been frozen and any modification on the platform due to filtering devices will directly impact the schedules as well as the global cost of the project.

In some cases, these mitigating measures could be mutualized with other connectees of the same grid, or even totally avoided.

In this context it is worthwhile to make sure that the constraints imposed are both coherent and realistic in order to avoid unwanted expenses. Nevertheless, some of these assumptions are therefore to be discussed with all stakeholders at a very early stage of the project development.

Two windfarms (one finished and one in development) are taken into consideration to present the different findings.


For windfarm developers:

For substations EPC contractors:



For project 1

For project 2


This paper gives an overview of the harmonic issues that can arise in offshore windfarms projects in order to enable all stakeholders to take the appropriate actions along the project schedule, since the project development until the detailed engineering phase.

If proposed recommendations are followed, the number of available levers to mitigate any exceedance is maximised. Also, the probability to mitigate the problem with an optimum solution is increased as the basic designs can be adapted to cope with harmonics.