The accumulation characteristic of surface charges on GIS Insulator under switching impulse voltages in SF6

Abstract

According to the advantages of smaller volume, smaller flooring space, and better dielectric performance and so on, Gas Insulated Switchgear (GIS) has been widely used in transformer substations. The disc insulators play a critical role in determining the insulating strength of GIS, while the accumulated surface charge on the insulator is the key factor for its insulating properties. The insulators of GIS will withstand the switching impulse voltage as a result of complex operating conditions. The present paper adopts electrostatic capacitance probe to develop a surface charge measurement system which can measure the surface charge on the actual disc insulators of GIS. Through the structure optimization, the charge leakage of designed probe is very small. This paper studied the effect of amplitude and pulse number of switching impulse voltage on the accumulation characteristic of surface charges on GIS insulator in SF6. The experimental results indicate that, under the switching impulse voltage, no matter positive or negative, the surface of insulator accumulates both positive and negative charges, but the amount of negative charges is larger than that of the positive charges. With the increase of amplitude and pulse number of positive switching impulse voltage, there is an obvious increase on the average amount of surface charge accumulation. However, under the negative voltage, the average amount of surface charge accumulation firstly increases and then decreases with the increase of amplitude, and which could rarely be influenced by the increase of pulse number of voltage.