Optimization of grading ring design for a new UHV equipotential shielding capacitor voltage transformer

A conceptual design of a new UHV equipotential shielding capacitor voltage transformer (CVT) with high precision, fast transient response, and no field calibration was proposed as a Chinese invention patent to meet the requirements of power systems on the accurate measurement of network voltage and fast operation of relay protection. This paper does not pretend to introduce its design concept and operation principle. The main purpose of this paper is to present the electric field calculation and analysis of grading ring configuration for this new CVT, as well as the optimization of design. When entering into UHV voltage level, the structure height of CVT greatly increases which gives rise to more obvious effect of stray capacitance to the ground and high voltage lead. Thus, the voltage distribution along the axis of CVT becomes quite uneven, and the surface electric field intensity of the top flange is very high. To improve the voltage distribution and reduce the excessive surface electric field intensity, grading rings should be properly configured and installed. As the UHV CVT is a thin high product without insulating pull rods on site, the grading rings causes the mechanical strength and aseismic performance to become worse, and leads windward area to increase. Thus the goal of the optimization of grading ring design is to minimize the dimensions while ensuring the technical requirements of electric field intensity. The 3D simulation model is developed using the finite element method to conduct the electric field calculation and analysis of various grading ring configurations. The influence of the location and structural parameters of the grading ting on the surface electric field intensity is investigated. The optimal design of the grading ring is obtained.