Investigation Of Harmonics And Calculation Of Harmonic Losses In Distribution Systems

Conventional distribution systems are designed to operate at single and constant frequency and specified voltage levels of constant magnitudes. However, the increasing use of nonlinear and electronically switched loads in distribution systems has led to higher harmonic distortion for both load voltage and current waveforms. Many harmonic studies have concentrated on large nonlinear loads such as variable frequency motor speed controller and large power converters as the main contributors to distribution system harmonics. However, single capacity is small, but a huge number of small non-linear equipment has not been given due attention. Now, residents of China's total electricity demand ratio is 12%, while the United States is 36%, China's residents electricity demand have very big room for growth, so research low-voltage load and distribution harmonic situation has long-term significance.We did the field investigation of low-voltage appliance load. The effect of them on the harmonic distortion is studied. Also we did the data acquisition in the 0.4kV distribution systems. The field data shows that non-linear loads can be a dominant effect with respect to harmonic distortion and power factor. A comprehensive investigation on the neutral and the phase current distortion levels behind the low voltage transformer has been carried out in the realistic distribution systems.According to the actual measured data, a research on problems caused by harmonic current and the influence of harmonic current on distribution system is carried. The effect of low-voltage appliance load on the harmonic distortion is studied. The field data shows that appliance load can be produces much harmonics and distortion power, as well as lower power factor, so it is a dominant effect with respect to reactive power and power factor of distribution network. A comprehensive investigation on the neutral and the phase current distortion levels behind the low voltage transformer has been carried out in the realistic distribution systems. Investigation presents an extremely amount of neutral current full with triple harmonics and phase current full with odd harmonics. a research on the influence of harmonic current on distribution system finds that three phases unbalance is commonly in the three-phase four-wire distribution system, harmonic current amplifies, neutral current over sizes, power losses increases, transformer contribute drawdown and so on.Harmonic power which is caused by the same frequency harmonic current and voltage increases the loss of power system, and understanding the harmonic loss ratio of the power network has guiding significance for the power company to draw up conserve energy measure. This paper compares and analyzes relative merits of the methods of estimating Power system harmonic loss and builds a simple model of calculation harmonic loss based on real power network and actual measured data. Harmonic loss and its share of total net loss ratio are analyzed in the paper.It is proved with theoretic analysis that harmonic distortion power is one important factor of which affect power factor, and in nature the harmonic distortion power is the energy transformed between power supply and appliance. Based on the analysis of the power factor and reactive power, we find that the harmonic flow in the power system not only increases power losses, but also brings about distortion power which is much greater than the traditional reactive power, and seriously reduces the power factor of the line, leading to the distortion power losses greater than the losses caused by the traditional reactive power flows. Clearly, the management of harmonic has great significance in reducing power system losses and improving power factor. Finally, this paper proposed that reactive power compensation should include traditional reactive power compensation and distortion power compensation when harmonic exists. In addition to, we analyze the characteristics of the filter and the applicability of different harmonic compensation based on the harmonic situation and different types of load, which is useful for management of harmonic.The analysis uses the time domain approach and utilizes the Alternative Transients Program (ATP) to model the different harmonic producing devices. The analysis proves that the models are identical with the realistic distribution systems. At last, harmonic power of appliance load and its effect on distribution network is emulated utilizing the three-phase four-wire system model.