Abstract

Stray capacitance can seriously affect the behavior of high-voltage devices, including voltage dividers, insulator strings, modular power supplies, or measuring instruments, among others. Therefore its effects must be considered when designing high-voltage projects and tests. Due to the difficulty in measuring the effects of stray capacitance, there is a lack of available experimental data. Therefore, for engineers and researchers there is a need to revise and update the available information, as well as to have useful and reliable data to estimate the stray capacitance in the initial designs. Although there are some analytical formulas to calculate the capacitance of some simple geometries, they have a limited scope. However, since such formulas can deal with different geometries and operating conditions, it is necessary to assess their consistency and applicability. This work calculates the stray capacitance to ground for geometries commonly found in high-voltage laboratories and facilities, including wires or rods of different lengths, spheres and circular rings, the latter ones being commonly applied as corona protections. This is carried out by comparing the results provided by the available analytical formulas with those obtained from finite element method (FEM) simulation, since field simulation methods allow solving such problem. The results of this work prove the suitability and flexibility of the FEM approach, because FEM models can deal with wider range of electrodes, configurations and operating conditions.

Highlights

  • The calculation of capacitance formulas has received little attention compared to the analysis of inductance calculation formulas [1,2]

  • Due to the lack of available experimental data because of experimental difficulties related to the small signal to be acquired and noise immunity, the results provided by the formulas are compared with the results provided by finite element method (FEM) simulations

  • This work has analyzed the behavior of several approximate and exact formulas to calculate the capacitance to ground of high-voltage electrodes with different geometries

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Summary

Introduction

The calculation of capacitance formulas has received little attention compared to the analysis of inductance calculation formulas [1,2]. Nearby surfaces separated by an insulating medium such as air, subjected to different electric potentials, induce a stray or parasitic capacitance, and this configuration acts as a capacitor. High voltages and high frequencies tend to amplify the effects of the unwanted stray capacitance. The analysis of stray capacitance effects is of interest in different disciplines, including electrical engineering, high-voltage applications, radio engineering or physical sciences, among others [3]. Different studies prove that the stray capacitance produces an uneven voltage distribution across each insulator unit in a high-voltage insulator string [4,5]. The effect of the stray capacitance is to reduce the efficacy of each additional insulator unit due to the non-linear voltage distribution [6]

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