Research on current sensor adapted for partial discharge detection in inter-turn insulation of wind turbine generator

The condition monitoring and diagnosis of insulation system of wind turbine generator (WTG) has become more and more important in recent years. Previous studies have shown that the partial discharge (PD) signals in the inter-turn insulation under induced impulse voltage may probably reflect the information of insulation condition. In this paper, a new type of non-contact current sensor on the basis of electromagnetic induction is designed. The sensor is sensitive to the high frequency low amplitude PD current signal and have flexible and thin framework on consideration of the spacing limitations and convenience of the WTG winding-end measurement. The basic concepts and principles of the sensor design are illustrated, proper materials are selected. The transfer characteristic of the sensor is frequency dependent, so a signal processing program based on Fourier analysis algorithm has been designed to reconstruct the time-domain input current signal from output voltage signal according to certain transfer characteristic of the sensor. Before practical application, the transfer characteristic of the sensor has been studied and tested. In order to verify the feasibility and effectiveness of the new sensor design, trial sensors have been prepared and put into experiment on a winding model in the laboratory. The artificial defects with the air gaps of 0.2mm thickness and 1mm diameter were attached between any two adjacent turns of an intact WTG stator coil for simulation of inter-turn void defect. 150V∼650V impulse test voltage were applied on the inter-turn insulation of the coil with artificial inter-turn air void defect and the PD signals are measured at the same time. The test results indicate that, the newly designed non-contact current sensor has good potential in inter-turn PD detection for WTG.