Analysis And Measure On Harmonics Of Power Distribution Network

Power is supplied to consumers with rated frequency and voltage in powersystems and the quality of electrical energy is evaluated by these two factors. But it'shard to evaluate the quality only with these two factors and the problems of waveformaberration and imbalance of voltage and current in 3-phase AC power systems can alsoaffect the quality. Nowadays, with the development of high-power electronics and itswide applications, power equipments, consumers and communication networks havebeen badly affected by large numbers of non-liner loads in power systems. Therefore,waveform aberration has been a considerable problem for the people.It's necessary to take practical measurement and treatment researches to solve theproblem of harmonics in power networks as well as having theoretic studies. For thecomplexity of the harmonics problem in power systems, deeply analysis with the resultof practical measurement is necessary. Thus, reliable measure methods and equipmentsare required to long-time on-line monitor. Nowadays, FFT algorithm is usually used inthe harmonics analysis equipments. The reason for the error produced by harmonicsmeasuring has been analyzed and the error of the algorithm has been analyzed andsimulated in detail in this paper. The measure results are unbelievable because thenon-periodic attenuation components are used in the algorithm and there will be errorsthat are hard to be compensated when measuring fluctuating harmonics loads. Animproved Fourier algorithm for harmonics measurement has been brought out and themeasure results are more exact by measuring the non-periodic and periodical harmonicsload components by the way of utilizing the symmetry of periodical components andeliminating the non-periodic attenuation components. According to GB/T 14549-93, anautomatic harmonics analysis and calculation method has been brought out based onDSP and industrial control computer workstation. This method has a high calculationprecision and is suitable for long-time on-line monitor. The hardware and softwaresystem of the harmonics measure equipment have been designed based on DSP and theharmonics monitor and analysis computer software for transformer substation has beendeveloped. The study conclusion in this paper will be a great help to improve the qualityof electrical energy, analyze the reason for harmonics and find the reasonable harmonicscontrol scheme.