Study On Propagation Characteristics Of High-order Harmonics In Power Grid

With the current rapid development of power systems,especially the rapid advancement of power electronics technology,PWM technology is widely used.This new technology has shown its advantages technically and economically,but it also brings a lot of The harmonics caused the distortion of the system voltage and current waveforms,which seriously affected the power quality.Compared with the traditional harmonics,the harmonic characteristics of the power grid have also undergone new changes,gradually showing new features such as wide-frequency domain harmonics,increased medium and high frequency harmonic content,and multiple types of harmonic interaction.When high-order harmonics pass through transmission lines and power transformers,situations such as resonance amplification will occur,which will have a greater impact on the stability and safety of the power system.Therefore,study the propagation characteristics of harmonics in the power grid and understand the harmonics The law of transmission is very important.In this paper,considering the electrical coupling between transmission lines and power transformers in the power system,a harmonic model of power system components and different transmission lines and power transformers is established,and the propagation characteristics and resonance of high-order harmonics in the power system model are analyzed.Case analysis based on the actual waveform.The research results show that:(1)Transmission lines usually have zero resonance points and pole resonance points.In general,the resonance point frequency is very high.As the length of the line increases,the resonance point frequency will decrease,but the transfer coefficient will increase.The resistive and inductive load will not affect the resonance point of the line,but the increase of the capacitive load capacitance will reduce the frequency of the line resonance point,and the change of the load will also change the transfer coefficient.(2)Transformers usually have resonance points.Generally,the resonance point frequency is very high.The resonance point frequency is related to the load and the parameters of the transformer itself.When the load is resistive or inductive,it will not affect the resonant frequency of the transformer,but the change of resistive load will change the transfer coefficient,and the inductive load will not affect the transfer coefficient;capacitive load will reduce the resonant frequency of the transformer;The transformer’s own leakage reactance and capacitance parameters will also affect the transformer’s resonance point frequency.(3)The system resonance point frequency of the transmission line and transformer is very high when the line length is short,but it will decrease with the increase of the line length.When the resonance point frequency drops to a very low value,the harmonic frequency The transfer coefficient will decrease as the frequency increases;the line impedance will increase sharply at high frequencies,and the harmonic transfer coefficient will gradually decrease.