Research On Overvoltage Suppression Strategies For UHV Half-wavelength AC Transmission Lines

The energy distribution and the load center in our country show the trend of reverse distribution.According to this trend,the long-distance large-capacity transmission method will become an important guarantee for the continuous and effective supply of national energy.UHV half-wavelength AC transmission refers to an AC transmission method in which the transmission distance is equal to half(3000 km)of the power frequency wavelength(6000 km(50 Hz)).As an important method of long-distance large-capacity transmission,halfwavelength AC transmission technology stands out from its ultra-long-distance largecapacity AC transmission due to its unique advantages.However,due to the more severe transient over-voltages generated during the operation of long lines,the electromagnetic transient characteristics of UHV half-wavelength transmission lines are also very different from ordinary lines,and the suppression of over-voltages on half-wavelength transmission lines is worth attention the study.In this paper,MOA is selected to suppress over-voltage on half-wavelength transmission lines.As a kind of oxide surge arrester without gap,MOA has better protection performance than traditional surge arrester.Using its outstanding characteristics(non-linear volt-ampere characteristics),that is,in the normal operation of the line,it is equivalent to an open circuit(the current flowing through MOA is very small);When overvoltage occurs on the line,MOA resistance drops sharply,releasing the energy of overvoltage,and then it acts as a protection effect.Compared with other types of surge arresters,zinc oxide surge arrester is more suitable for suppressing over-voltage.Based on the voltage distribution characteristics of UHV half-wavelength transmission line and the over-voltage problem of the line,this paper establishes the relevant model of UHV half-wavelength transmission line by using the electromagnetic transient simulation software PSCAD/EMTDC.Based on PSCAD/EMTDC,the over-voltage distribution of UHV half-wavelength transmission line under four basic faults(i.e.single-phase ground short circuit(metallic short circuit),two-phase short circuit,two-phase ground short circuit(metallic short circuit)and three-phase short circuit)is simulated(the over-voltage after single-phase reclosing is considered).According to the distribution of overvoltage,the preliminary layout strategy of zinc oxide arrester for overvoltage suppression is proposed and the feasibility of the scheme is verified by simulation.Lightning strikes are common in nature,and UHV half-wavelength transmission lines are 3,000 kilometers long overhead lines.In the operating condition of the line,besides the distribution of overvoltage under four basic faults,the suppression of overvoltage caused by lightning should also be considered.In this paper,the simulation analysis of the lightning strike any transmission line and the ground wire,over voltage distribution on the line,and validate the presented preliminary layout strategy adaptability under the condition of lightning strike,If it is not feasible,the modified and improved scheme is further proposed,so that the proposed scheme is applicable to all four basic faults and lightning conditions,and then the feasibility of the simulation verification scheme is verified Mobility.