Resonance Characteristics in Offshore Wind Power Plants with 66 kV Collection Grids

Abstract

This paper presents a study of the influence of doubling the collection grid voltage on the electric resonances in the collection grid of large offshore wind power plants. This was done using wide-band models of most important passive components such as transformers and cables. Wide-band models based on measurements (black box) of transformers were used. Scaling of admittance matrix elements was used in order to adjust the voltage ratio of the measured wind turbine transformers to take into account the doubled voltage at the medium voltage side. It was shown that doubling the collection grid voltage decreases the main resonance frequency seen at the medium voltage terminal of the wind turbine transformers as well as the offshore substation transformer. The decrease was approximately 25 per cent when doubling the voltage and keeping the same number of turbines in a radial. When the number of turbines was doubled, there was a proportional decrease of the resonance frequency. Decreasing the main resonance frequency in offshore wind power plants might have an impact on the harmonic and transient behaviour and should therefore be investigated by developer