Observation Of Surface Charge For Composite Insulator And Re-search Of Its Influence Factor

With the continuous improvement of the transmission voltage grade, more andmore composite insulators are applied to transmission lines. Compared with thetraditional porcelain and glass insulator, composite insulator has many advantagessuch as light weight, high strength, strong ability to resist pollution flashover,convenient maintenance, and composite insulators are preferred especially in theheavy polluted areas. However, many charges will accumulate on the surface of theinsulator under the stress of high dc voltage, which can lead to electric field dis-tortion and sometimes result in flashover when the voltage is high enough. It is ofgreat significance to improve its insulation properties to study the surface chargeaccumulation.In order to investigate the surface charge accumulation phenomenon of highvoltage DC composite insulators, a new set of automatic surface charge detectiondevice for insulator with umbrella group is developed. The device adopts modifiedstatic capacitance probe, and transfers data by means of GPRS; LabVIEW platformis applied for data processing; a device is developed to drive the probe to scan theinsulator surface accurately. For composite insulator, this device can automaticallyachieve accurate measurement of the umbrella and the sheathing surface.Surface charge observation experiment platform is developed to measure thesurface charge distribution under different condition, and its influencing fac tors arestudied. Measurement results show that it has the largest charge accumulation onthe upper surface of the first umbrella of the cathode, most of which is of negativepolarity, and the surface charge distribution is very uneven. A s the extension oftime, the maximum density of negative charge increases greatly than the positivecharge, and multiple peaks appear under higher voltage. It has relatively obviouscharge accumulation near the filth when the umbrella skirt surface is locally con-taminated.For the surface charge accumulation caused by inconsistent current, this arti-cle uses the finite element software to simulate and analyze the surface charge dis-tribution. Results show that when the fouling layer covering on the surface of theinsulator has larger conductivity, the mode of charge accumulation caused by in-consistent current serves as a major role. When the surface fouling layer hassmaller conductivity or it is in a clean and dry condition, the non-uniform degree of surface conductivity is low only affected by the tangential field strength, whichdoes not play a major role in charge accumulation. In this case partial dischargenear the cathode provides the source charge, and the strong normal component ofelectric field of the umbrella skirt is the main cause of large amounts of chargeaccumulation on the surface of the first umbrella.