| Nowadays,the development of science and technology make a spurt of progress. Electric power is the foundation of all walks of life.The security of the power system power is an important guarantee for the safety in production, at the same time, economic power can also reduces economic losses.Therefore, electric power equipment must be carried on the effective protection. Metal Oxide Arrester (MOA) is widely used in electric power system. It is installed in parallel with the protected equipment. When lightning occurs, MOA will rely on its own nonlinear characteristics to protect the electric power equipment. Analysis of the running state is the premise to ensure the normal work of the lightning arrester, and it has the vital significance to the safe operation of power equipment and power system. At home and abroad, there are many methods of analysis on the running state of MOA, such as the total leakage current based method, harmonic analysis, harmonic analysis, three compensation method, the double "AT" method, and so on. These methods can reflect the operation status of MOA in a certain extent, but the detection accuracy is not high, even leads to misjudgment of the operation state of MOA.So these analysis method of the operation state of MOA must be improved to enhance its accuracy.Based on the total discharge current, this paper will use the new threshold of translation invariant wavelet denoising, To suppress the pseudo Gibbs phenomena of traditional threshold denoising method, in order to obtain more accurate the arrester leakage current signal.Through the use of simulation software to verify the effectiveness of the method. It can accurately determine the MOA advanced aging condition. But the early and middle aging are difficult to judge.In order to better determine the MOA early and middle aging condition, this paper puts forward the improved algorithm based on capacitance method. According to the interference of harmonic amplitude and phase uncertainty,Direct measurement of resistive current operation state of MOA may lead to miscarriage of justice.Capacitance method does not exclude the impact of harmonic voltage on the three harmonic resistive current.So, this paper presents an improved algorithm.Through the simulation comparison of two methods, this paper analyzes the influence of different proportion and different harmonic harmonic phase. The harmonic resistive current amplitude increase with the amplitude and phase of the harmonic voltage.Two algorithms of the fundamental resistance leakage current is consistent.However, there are many errors by using capacitance method to analyze three resistance of harmonic currents. But in the new algorithm, it compensates the resistive leakage current component of harmonic voltage, by using the approximate phase current relationship,to get the exact value of fundamental and three harmonic resistive current. Finally, it provides a more accurate judgment of the early and middle aged state MOA. But when the lightning arrester is in advanced age,the new algorithm error sometimes larger than the capacitance method,and the trend of measured value of three harmonic resistive current is very untidy, so,this new algorithm is invalid,at this times.It must integrates methods described in the previous chapter for completing the late aging judgment.Based on the above two methods of analysis,we can make scientific assessment of MOA in early, mid and late aging.There is an important significance for the safe operation of the power system... |
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