| The total current,resistive current and third harmonic component of the leakage current of zinc oxide arrester are important indicators to judge its aging degree.Because the leakage current is very weak,the current measurement method is easily affected by the harmonics in the power grid.Especially for the MOA working in the converter station,there are many harmonics in the leakage current signal,which lead to the error of measurement results and can not accurately judge the aging condition of MOA.Lock in amplification algorithm can extract the amplitude and phase information deeply embedded in the noise signal,which is often used in weak signal detection.In this paper,lock-in amplification algorithm is used as the measurement method to design the leakage current detection device.Firstly,the vector relationship between resistive current component and capacitive current component of leakage current is analyzed based on the principle of zinc oxide arrester leakage current.Comparing the volt ampere characteristic curve of Zn O arrester before and after aging,the change of leakage current and its resistive component is analyzed,and the influence of Zn O arrester aging on the harmonic component of leakage current is explored.Secondly,in order to solve the problem of extracting leakage current in noise environment,the phase-locked amplifier algorithm is used.The anti noise ability of phase-locked amplifier algorithm to white noise and harmonic noise is simulated and analyzed under different signal-to-noise ratios.The ability of phase-locked amplifier algorithm to extract leakage current signal buried in noise is verified,and the possible errors caused by a / D conversion resolution and sampling frequency are analyzed analysis.Finally,a leakage current experiment platform based on YXDSP-F28335 development board is designed,including signal sampling circuit,conditioning circuit,power supply circuit and serial communication circuit.The leakage current with harmonic and other noises is measured by lock-in amplification algorithm. |
