Causes of currents in the wind turbine bearings

Report, 2017

In some wind turbine nacelles, a current on the shaft is detected which can wear off the bearing gradually. The high maintenance cost is the main motivation of investigate the root cause of the current in the bearing. In the case of Big Gleen, the biggest wind turbine in Sweden, measurement is taken from eight critical points in the nacelle and Fast Fourier Transform(FFT) study on the data is carried out. Several possible root causes are proposed and the current in the shaft is studied by simulating the magnetic field around the shaft in COMSOL. In an opposite way, how much induced voltage to generate such amount of measurement current in the foot of the bearing is also simulated. As for the measurement result, large amount of current is detected through the grounding cables which is highly suspicious. For the simulation result, based on specific assumptions, the possible root cause of the current is the induced voltage due to the power cables over the shaft. However, to verify the proposal of induced voltage, more accurate measurement equipment is needed for future work.