Sensitivity of Nodal Admittances in an Offshore Wind Power Plant to Parametric Variations in the Collection Grid

The paper presents sensitivity studies on nodal admittances in the offshore wind farm to different parameters of the collection grid cable system, including length of cable sections and actual layout configuration. The main aspect of this investigation is to see how parametric variations influence admittance and, consequently, voltage transfer in frequency domain. The simulation model of the offshore wind farm was build based on the main components in turbines and the collection grid. The simulation results were compared with data from time domain measurements and showed good agreement. A number of nodes were selected for evaluation of the admittances: the connection point to the external grid, a point at the substation and at each wind turbine. The results show that at specific locations resonances occur, where the admittance increases significantly in the 10-100 kHz range, depending on the location. On the other hand, anti-resonance peaks occur in the 0.1-10 kHz range and these are not location dependent. Resonant peaks at higher frequencies are proved to be determined mainly by collection grid cables. Voltage transfer measurements from the wind turbines low voltage side to the external grid connection show that high frequency components are highly damped at that distance. A considerable match was found between high frequency peaks in the admittance scans and the voltage transfer at the collection grid. This proves that some particular frequencies cause series resonances to occur at particular locations at the wind turbines medium voltage side.