Experimental teaching on gas-solid interface discharge and its charge accumulation characteristics under impulse voltage

Surface insulation represents the weak link in gas-solid composite insulation systems. The development of high-voltage direct current transmission technology has exacerbated surface charge accumulation on insulators. Surface charges distort local electric field distribution and cause an abnormal decrease in surface insulation strength under polarity reversal or impulse overvoltage, thereby severely compromising power system operational safety. Therefore, researching gas-solid interface discharge and its charge accumulation characteristics is essential for clarifying the failure mechanism of insulation structures and providing a theoretical basis for optimizing the insulation design of electrical equipment. Based on the surface discharge observation platform and surface charge characterization technology, such a research scheme is proposed.

An experimental surface discharge observation platform is established. An impulse voltage generator is utilized to output the standard lightning impulse voltage. Surface-discharge voltage and current waveforms are measured by a resistance voltage divider and a current coil. The discharge luminescent images are captured by a single-lens reflex camera. A polymethyl methacrylate square sheet is adopted as the insulator. The electrostatic probe and dust figure methods are used to measure the charges accumulated on the insulator surface, following discharge. In this experiment, the surface discharge test is first conducted in the air, after which the charges accumulated on the insulator surface are characterized. The development process of surface discharge in the air is simulated by the fluid simulation model using the discharge module in COMSOL Multiphysics.

Experimental results show that discharge current pulses are measured during surface discharge, with filamentary positive surface streamers being simultaneously observed through luminescent images. The surface charge measurement indicates that the positive and negative charges exhibit dendritic and circular distributions, respectively. Under positive and negative voltages, the surface-accumulated charges are dominated by positive and negative polarities, respectively. The polarity effect ensures that negative streamers encounter higher propagation resistance than positive streamers, resulting in significantly shorter negative streamers than positive streamers. Surface discharge intensifies with the increasing voltage amplitude, promoting surface-charge accumulation after discharge. Simulation results demonstrate that initial electrons converge significantly in the needle tip region under positive voltage, initiating an electron avalanche that forms a positive streamer after developing to a certain extent. This propagates outward from the needle electrode along the solid dielectric surface. The electric field is concentrated at the streamer head, whereas the channel interior comprises an electrically neutral plasma, resulting in very low electric field strength.

This study analyzes the influences of voltage polarity and amplitude on surface streamers in the air, clarifying the evolution characteristics of surface streamers by measuring electrical signals, optical signals, and surface charge, as well as simulating surface discharge. The vivid and intuitive experimental results are essential for improving teaching effectiveness. The experiment involves a variety of equipment and methods, enhancing students’ experimental and simulation capabilities while cultivating their innovative spirit and scientific literacy.