| It’s inevitable to withstand AC and DC voltage for DC converter valve which is the core equipment of HVDC transmission.With the improvement of the voltage level,the parts such as fittings and shields of converter valve are subjected to AC and DC superposition electric field and corona discharge may occur due to the field strength is too large.While the decrease of air pressure and the change of environmental humidity have a certain influence on the corona discharge.In order to realize the optimal design of the insulation inside the valve under composite voltage,it is also necessary to consider the effect of air pressure and humidity on the corona discharge characteristics of the electrode under combined AC and DC voltage.In this paper,a self-designed divice is used to simulate the altitude and humidity.Secondly,the inhomogeneous field electrode represented by the rod-plate electrode and the slightly nonuniform field electrode represented by the shrinking electrode of shield of valve are selected as the experimental electrode.And it applied voltage in series to achieve the AC-DC composite voltage.Finally,a corona experimental platform of high voltage electrode which can adjust air pressure and humidity and achieve composite voltage was built based on the designed experimental device and the experimental electrode and the composite voltage circuit.It gave a study on the UV photon number produced by the corona discharge of the rod electrode based on the UV,which considering the influence o f the observation gain,the observation distance,the voltage component,the distance of the gap and the radius of the rod electrode.Finally,the appropriate observation gain,observation distance and corona onset voltage criterion are selected for experiments,which lays the foundation for the subsequent experiments.Then,it gave a reaserch on the UV characteristics and corona onset voltage characteristics of the rod-plane electrode under different pressure and humidity under composite AC and DC voltage by using the corona test platform and the corona onset voltage criterion.Experimental results show that the intensity of the corona discharge increases and the corona onset voltage decreases as the pressure decreases.Then with the increase of humidity,the corona discharge intensity of the rod electrode is almost constant and the corona onset voltage is also basically unchanged when the rod electrode is applied positive DC-AC composite voltage.The corona discharge intensity of the rod electrode increased and the corona onset voltage was decreased when the rod electode was under the negative DC-AC composite voltage.The AC voltage component of the corona inception point decreases linearly with the increase of the DC voltage component under different AC/DC voltage ratio.At last,it gave a reaserch on corona diacharge characteristics of the slightly nonuniform field electrode represented by the shrinking electrode of shield of valve under different pressure and humidity under AC-DC composite voltage.Experimental results show that the corona discharge onset voltage decreases with the decrease of air pressure,and the initial corona discharge voltage decreases with the increase of humidity.The AC voltage component of the corona inception point decreases with the increase of the DC voltage component.But the AC voltage component is nonlinear with the DC voltage component. |
