The distributing characteristics of sediment deposited on pin-type grading electrodes in inner cooling circuit of HV converter valve

Inorganic sediments frequently deposit on the pin-type grading electrodes installed in the inner cooling circuits for high voltage converter valves. This investigation focuses on the distributing characteristics of deposited sediments. Field data have been collected from three ±500kV converter stations. Sediment distributions corresponding to different valve tower structures are summarized. The relationships between sediment thickness and electrode locations in both horizontal and vertical components of converter valve are analyzed. The chemical compositions of field-collected sediment samples are analyzed by means of energy dispersive spectrometer (EDS). Electrical insulating properties of the samples are measured. The results indicate that the deposition degree of the sediment is mainly dominated by the electrical current through the pin-type grading electrode. The electronegative sediment particles tend to deposit on the grading electrodes with positive polarity. The deposited sediment is mainly composed of aluminum oxide compounds and may impact the uniform effect of the grading electrode.