Abstract
The capacitive voltage transformer (CVT) is a special measuring and protecting device, which is commonly applied in high-voltage power systems. Its measurement accuracy is affected seriously by the stray capacitances of the capacitance voltage divider (CVD) to ground and other charged parts. In this study, based on the boundary element method, a mathematical model was established firstly to calculate the stray capacitance. Then, the voltage distribution of the CVD was obtained by the CVD’s equivalent circuit model. Next, the effect of stray capacitance on the voltage distribution and the voltage difference ratio (VDR) of CVD was analysed in detail. We finally designed three types of shield and optimized their structure parameters to reduce VDR. The results indicated that the average deviation rate between calculated and experimental measured voltages is only 0.015%; that is to say, the method has high calculation precision. The stray capacitance of the CVD to ground is far larger than that of the CVD to the high-voltage terminal. It results in the inhomogeneous distribution of voltage and the increase of VDR. For the test CVT, its VDR exceeds the requirement of class 0.2. Among all of the three types of shield, the C type reduced the VDR of the test CVT the most. After optimizing the structure parameters of C-type shield, the VDR is further reduced to 0.08%. It is not only in accord with the requirement of class 0.2 but also has an adequate margin.
Highlights
Introduction e Capacitor VoltageTransformer (CVT) has high dielectric strength, fast transient response, wide dynamic range, low power consumption, and nonferromagnetic resonance with power systems
Stray capacitance affects the performance of high-voltage devices seriously, such as voltage dividers, insulator strings, modular power supplies, and measuring instruments [6]. us, it must be considered in the design of high-voltage devices. e stray capacitances of the Capacitor VoltageTransformer (CVT) to ground and other charged parts play an important role in causing the voltage difference ratio (VDR) of the CVT [7]
It exceeds the requirement of class 0.2. erefore, it is urgent to study the influence of stray capacitance on the VDR of CVT and explore solutions to reduce the adverse effect of stray capacitance, so as to ensure the safe and stable operation of the power system
Summary
Transformer (CVT) has high dielectric strength, fast transient response, wide dynamic range, low power consumption, and nonferromagnetic resonance with power systems. It can reduce the head steepness of lightning shock and be used as a coupling capacitor for the power carrier communication [1,2,3,4]. For the CVT applied in the ultra-high-voltage level, the effect of stray capacitance on its VDR is more serious [8]. The VDR of CVT which applied in the 750 kV power system caused by the stray capacitor is larger than 0.2% [9] It exceeds the requirement of class 0.2. It exceeds the requirement of class 0.2. erefore, it is urgent to study the influence of stray capacitance on the VDR of CVT and explore solutions to reduce the adverse effect of stray capacitance, so as to ensure the safe and stable operation of the power system
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