On-Line Partial Discharges Sensing Method in Aeronautics for AC and PWM Voltages: Optimizations and Limitations

The availability of an effective and reliable partial discharges (PD) sensing method gains importance for aerospace, as the tendency, to install more electrical power into the aircraft systems, comes along with higher voltages. Furthermore there is the requirement to detect PD in harsh EMI environments, which mainly reflects the increased use of power electronics. The presented paper describes a suitable approach for PD-detection, based on the adaptation of a capacitive coupler, which allows online and non-intrusive measurement even with PWM-operation of power electronics. The geometrical implications of the adapted sensors are outlined, based on several experiments with the focus on the signal-to-noise ratio. In order to ensure the relevance of the results, typical components of the aircraft, e.g. transformers and motors, have been taken into account. The validity of the new sensor's results has been assessed by comparison with standard PD-measurement equipment. Here, the limits of both approaches could be identified and conclusions for their application derived. The works done the last months have highlighted the different natures of some discharges, depending on the applied voltage. These natures have been identified by measuring the frequency content of the discharges. Obviously, the frequency characteristic of the PD-detection-method plays an important role. This paper describes the different types of discharges which have been measured and bring a description of their nature. The paper concludes with a discussion of the results. The advantages and drawbacks of the new sensor are given and a comparison with the old version is made. Finally, necessary future work is identified.