Research And Development Of Harmonic Voltage Correction Measurement Device Based On CVT

Capacitor voltage transformer(CVT)is a kind of power transformer widely used in high voltage measurement.Because of the special structure of CVT,it not only has the ability of accurate fundamental wave measurement,but also has the characteristics of small volume and low cost.However,it is not suitable for direct harmonic measurement.In the modern power grid,the problem of harmonic pollution is becoming more and more serious.As the basic acquisition tool of voltage signal,voltage transformer must be able to meet the new needs of the development of power industry.This paper analyzes the limiting factors that CVT can not be directly used in harmonic measurement,including structure,stray capacitance and core element.This paper introduces the existing technology of using CVT to realize harmonic voltage measurement.After comparing the advantages and disadvantages of each technical scheme,the correction curve method is used as the guidance method of harmonic correction measurement device.The hardware of the device consists of signal acquisition circuit,data processing circuit,human-computer interaction circuit and power circuit.The signal acquisition circuit is composed of micro PT,voltage follow circuit,low-pass filter circuit and A/D circuit to realize A/D conversion of harmonic signal below 2.5KHz at the secondary side of CVT;the data processing circuit is based on STM32F407 to realize program flow control and signal analysis;the human-computer interaction circuit provides data visualization and parameter input;the power circuit is for each device The module provides suitable working power.In the software,the harmonic analysis algorithm,the correction curve method and the interpolation method to eliminate the frequency fluctuation are introduced.The control of hardware module and the program expression of CVT harmonic voltage correction measurement algorithm are completed on STM32F407 by C programming language.In addition,using C# programming language,the upper computer is designed on the PC side,which realizes the synchronous display and storage of data.In this paper,110 k V CVT model simulation experiment is set up,the experimental results verify the correctness of the device software and hardware design,and preliminarilyverify the harmonic measurement performance of the device.Through further field experiments,it is proved that the device has the ability to achieve accurate harmonic measurement under voltage amplitude and frequency fluctuation.At the same time,by comparing the data of RCVT,CVT and the device,the accuracy and feasibility of the curve correction algorithm are verified.The device realizes the harmonic voltage correction measurement without changing the internal structure of CVT.It is portable and safe,and is suitable for large-scale application.