Research On Key Technologies Of High Voltage Transmission Line For RF Negative Ion Source

Neutral beam injection is an essential and effective heating and current driving means for fusion plasma.Its physical mechanism is clear and its heating effect is direct and significant.It not only provides essential,direct and effective support for the current fusion experimental device to carry out high-level physical experiments near the core,but also is the most effective tool for the proposed fusion reactor to realize fusion ignition and combustion plasma control.With the deepening of nuclear fusion research,higher requirements are put forward for the operating parameters of neutral beam injection system.Facing the requirements of high-energy and long pulse in the future neutral beam injection system,the neutral beam injection system using high-power RF negative ion beam source has become one of the most feasible options at present.The high-voltage transmission line of the RF negative ion source neutral beam injection system is the link connecting the power supply including negative ion acceleration power supply,negative ion extraction power supply and negative ion source auxiliary power supply with their corresponding loads,providing power supply required by certain design indexes for each load,and providing transmission channels for various diagnostic and measurement signals of RF negative ion source,which are suspended at-400 kV high potential.Therefore,the research and design of high-voltage transmission line is of great significance.In this paper,the key technical problems such as(1)the insulation gap design of high-voltage transmission line,(2)the insulation structure design of post insulator,and(3)the suppression of insulation defects are solved by combining theoretical analysis and experimental research,including:(1)For key technology Ⅰ,the simulation analysis and design of insulation gap of high-voltage transmission line are carried out:the influence laws of the positions of high-voltage conductor and the inner radius of grounding shielding shell,corner radius and corner angle on the distribution parameters of electric field and equivalent distributed capacitance are studied,and the structural parameters of straight section and corner section of high-voltage transmission line are determined.The research results show that for the straight section of high-voltage transmission line,taking the center position of grounding shield shell as the reference point,when-200 kV high-voltage conductor is located in the center position of grounding shield shell with the downward offset of 70 mm,and-400 kV high-voltage conductor is located in the center position of grounding shield shell with the left offset of 120 mm and the upward offset of 310 mm,the maximum internal electric field intensity of high-voltage transmission line and the maximum internal surface electric field intensity of grounding shield shell are 2.64 kV/mm and 1.51 kV/mm respectively,the electric field non-uniformity coefficient is 1.87,and the equivalent distributed capacitance is 78.95 pF/m,which satisfy the design requirements of insulation;For the corner section of high-voltage transmission line,when the corner angle is 90° and the corner radius is from 50 mm to 150 mm,the maximum internal electric field intensity of high-voltage transmission line is reduced from 3.18 kV/mm to 3.06 kV/mm,the maximum internal electric field intensity of grounding shield shell is reduced from 1.08 kV/mm to 0.73 kV/mm,the electric field non-uniformity coefficient is reduced from 2.21 to 2.15,and the equivalent distributed capacitance is increased from 82.12 pF to 94.70 pF,which also satisfy the design requirements of insulation.(2)For key technology Ⅱ,the insulation simulation analysis and design of post insulator of high-voltage transmission line are carried out:the insulation performance and influencing factors of main post insulator and metal inserts of high-voltage transmission line are numerically simulated,the influence characteristics of the structural parameters of main post insulator and metal inserts on electric field distribution parameters are analyzed,and the accumulation characteristics of the surface charge of solid-gas interface are studied,the structural parameters of main post insulator and metal inserts and the material properties of main post insulator are determined.The research results show that when the column radius of main post insulator is 70 mm and the radius,the embedding depth and the arc height of metal inserts are 50 mm,30 mm and 20 mm respectively,the maximum electric field intensity on the gas side is 4.81 kV/mm,the maximum electric field intensity on the side surface of main post insulator,the maximum tangential electric field intensity on the side surface of main post insulator and the maximum internal electric field intensity of main post insulator are 3.24 kV/mm,1.99 kV/mm and 4.47 kV/mm respectively,the maximum surface electric field intensities of high-voltage metal insert and low-voltage metal insert are 2.23 kV/mm and 2.22 kV/mm respectively,which satisfy the design requirements of insulation;When the bulk conductivity and superficial conductivity of main post insulator are 5×10-16 S/m and 10-18 S respectively,the maximum surface positive and negative charge densities of solid-gas interface are 52.52 μC/m2 and 57.04μC/m2 respectively,which will not affect the voltage stability and satisfy the design requirements of insulation.(3)For the key technology Ⅲ,the influence characteristics and suppression measures of insulation defects are studied:the variation characteristics of distribution parameters of electric field with the size and position of bubble defect are analyzed,the distribution of electric field of particle trap under different structural parameters is studied,and the structural parameters of particle trap are determined.The results show that the maximum internal electric field intensity of bubble defect exceeds 3 kV/mm no matter where the bubble defect appears in the main post insulator.Therefore,in the production and manufacturing process of post insulator,quality control must be strengthened to avoid bubble defects;Under the action of DC voltage,when the slot depth and the slot width of particle trap are 6 mm and 8 mm respectively,the opening angle of particle trap is 60° and the outer radius of particle trap is 525 mm,the particle trap can achieve 97.36%shielding effect of electric field.(4)The insulation performance test research of high-voltage transmission line test samples is carried out:Based on the breakthrough of the above three key technologies,the high-voltage transmission line test sample is developed,the insulation performance test-bed of the high-voltage transmission line is built,the insulation performance of high-voltage transmission line test sample under different SF6 pressure is studied,and the leakage current laws of the high-voltage transmission line test sample under different loading voltage/different SF6 pressure are obtained.The test results show that the maximum leakage current under 500 kV loading voltage is 0.472 mA,and the test sample of high-voltage transmission line satisfies the design requirements of the insulation.To sum up,this subject solves the key technical problems in the high-voltage transmission insulation design of RF negative ion source neutral beam injection system,such as the insulation gap design of high-voltage transmission line,the insulation structure design of post insulator and the suppression of insulation defects,and puts forward a set of the insulation design scheme of-400 kV high-voltage transmission that can be applied to the RF negative ion source neutral beam injection system,which provides a theoretical basis for the engineering design and construction of high-voltage transmission line of test-bed for the RF negative ion source neutral beam injection system.