Prediction study on positive DC corona onset voltage of rod-plane air gaps and its application to the design of valve hall fittings

Corona inception can be viewed as the release of capacitive energy stored in the electric field. A new prediction method of the corona onset voltage based on electric field features and support vector machine (SVM) is proposed in this study. This method was used to predict the positive DC corona onset voltage of the rod-plane air gap. The predicted results were compared with the experimental values and the calculated values of the existing methods. Then, the corona onset voltage of the shielding sphere used in a valve hall of +/- 660 kV DC converter station was measured and predicted by the SVM model and the photoionisation model. The safe values of corona inception electric field strength were obtained. By comparing the finite element numerical calculation results of the electric field strength with the safe value, it was proved that the corona would not incept on the surface of the shielding sphere under operating voltage. This method provides a new possible way to predict corona onset voltages of valve hall fittings used in HVDC transmission projects.