Design of an equipotential shielding 1000 kV capacitor voltage transformer

With the increase of the operating voltage and enlargement of the size of the capacitor voltage transformer (CVT), the additional measurement error caused by stray capacitance coupling and leakage current along the polluted surface of the CVT becomes noticeable. The equipotential shielding CVT (EPS-CVT) was proposed and designed by the authors to mitigate these effects. An improved conceptual design option of the EPS-CVT is presented in this paper with special references to this study to improve the shielding effect without the increase of shielding capacitance. A proposed method of non-uniform capacitance configuration can improve the shielding effect significantly without an increase of the external shielding capacitance. Based on this achievement, the potential difference and the capacitive current exchange between the internal measuring system and external shielding systems are significantly reduced. In the evaluation of the shielding effect for the influence of stray capacitance, compared with a conventional CVT with equal capacitance, EPS-CVT can reduce the measurement error by two orders of magnitude. In addition, the measurement error caused by the leakage current can also be greatly reduced, especially for the reduction of the phase angle error. Based on the improved design method, a design scheme for an engineering application is proposed which can achieve effective shielding while ensuring as good a technical performance as the existing CVT.