EMT generic wind turbine model for offshore substation design

System Operator (TSO) is involved in the design of the Offshore Sub Station (OSS). A key challenge is that many design studies, such as insulation coordination, sizing of the neutral grounding transformer, or short-circuit withstand studies, depend directly on assumptions related to the wind farm itself. These assumptions include, for instance, the length of the interarray cables and section, and even more critically, the characteristics of the wind turbine generator systems (WTGSs).

However, this information, especially the EMT models of the turbines required to perform realistic transient simulations, is generally not available at the time of the OSS design studies and will not be provided by turbine manufacturers before 6 months of the handover. From experience, RTE has observed that it is quite common for studies to be performed using simple

Thevenin equivalent models to represent offshore wind farms. Such simplifications can lead to studies that are insufficiently accurate or even non-conservative. This is notably the case for short-circuit current studies, as well as for overvoltage studies following fault clearance.

This paper presents the approach implemented by RTE for an offshore grid connection project:

1) Starting from an existing generic model, RTE adapts it to make it compliant with the grid code, in particular for the voltage support during Fault Ride Through (FRT) performance and protection systems.

2) RTE shares this model with the OSS contractor for preliminary design studies.

3) This model is used for design purposes; once the vendor-specific turbine model is received, selected studies are repeated for validation and, if necessary, protection tuning. The focus of this paper is on the first step, with the main objective of developing a generic turbine model that can be shared with third parties:

 The turbine model must include realistic hypothesis for the hight voltage equipment  The model must be realistic, at least to the extent that its fault behaviour (FRT capability, reactive current injection) complies with the French grid code. To this end, a generic Type 4 (full converter) wind turbine model from the EMT software library was used. This model is fully open and therefore suitable for adaptation.

The first part of the paper provides a brief description of the base model used. The second part presents the grid code requirements implemented to enhance the model in line with RTE requirements. Validation tests are then presented. A case study illustrates the potential impact of using a generic turbine model compared to a simple Thevenin equivalent. Finally, the paper discusses open points and outlines planned future developments.