Research On Electromagnetic Conducted Interference For Intelligent Component Caused By Ground Potential Rise During Transformer Lightning Impulse Test

Smart grid is the development direction of electrical power system and the intelligent components are the key part.The GPR(Ground Potential Rise) caused by ground current when taking lightning impulse conducts to secondary cable,which makes detriment on the power port and has bad influences on its operation state.The paper researches on the conducted disturbance voltage of power port,which has important theoretical significance and practical value.Combining the science and technology project of State Grid Corporation of China 'Study on the Harm of Ground Potential Rising of 220kV and 500kV Substation to Transformer Intelligent and Related Protective Measures' and the Nation Science Foundation Project(Grant No.51177048)'Research on the Passive Wideband Modeling of Key Equipment in Transformer Substation',the calculation method of power port conducted voltage and the fractional broadband modeling method of key equipment are studied.The disturbance voltage when the 500kV transformer is taking lightning impulse test is researched.The interfering path and characteristic of disturbance voltage are studied.The specific innovation points are as following1.The transient voltage measurement system which is able to avoid space radiation interference and conducted interference is constructed.The experiment is taken based on the measuring system.The reason for GPR and the coupling path of the GPR conducted to power port are analyzed.The disturbance voltage characteristic is studied.2.The fractional frequency-dependent characteristics of oil-paper compound insulation is studied and the fractional lumped-parameter model for transformer considering the above characteristic is modeled.By combining the fractional vector fitting and synthesis method of fractional admittance function,the fractional two-port model of transformer is modeled,hich is more accurate and simpler than traditional model.3.Addressing the problem that fractional binary quadratic impedance function cannot be synthesized in s domain directly,a kind of synthesis method based on variable substitution and multivariable synthesis theory is proposed.The frequency characteristic of some transformer branch is fitted as specific fractional rational function and then synthesized by proposed method.The related active circuit of transformer can be translated into passive circuit.4.The stray capacitance of key equipment to ground grid is extracted and then fractional lumped-parameter model for ground grid considering frequency-dependent characteristics of dielectric constant is modeled.Combining the fractional vector fitting and synthesis method of fractional admittance function,the fractional four-port model of ground grid is modeled,which is more accurate and simpler than traditional model.5.A kind of synthesis method tor fractional admittance function with the same variable and order is proposed by cascading Tellegan circuit with two fractional energy storage components.The circuit doesn't need ideal transformer and only needs the minimum storage components.Some polynomial ot ground grid branch is lersed into specific rational function and then synthesized by the proposed method.The related active circuit of ground grid can be translated into passive circuit.6.Other key equipment in testing hall are modeled respectively.Based on the test loop and combining the transformer model and ground grid model,the disturbance voltage of intelligent power port is calculated.Result shows that(1)the common-mode disturbance of power supply without SPD is more than 20kV,which is highly more than the assigned voltage in IEC61000-4-5 standard and(2)the common-mode disturbance of power supply with SPD is less than 4kV and the difference-mode disturbance is less than 2kV.The conclusion in this paper can provide a reference to resist electromagnetic disturbance for intelligent components.