Study Of Ball Gap Triggered Discharge Characteristics Of Transformer Neutral Point Protection

Due to the defects of rod-stick gaps in transformer neutral protection devices,a new type of controllable gap(ball gap spark switch)instead of rod-stick gaps has been proposed,which is expected to solve the transformer neutral protection problem.However,due to the wide variety of lightning arresters,there are a variety of specifications for the diameter size of the matching ball gap spark switch,so the discharge characteristics and operating characteristics of the ball gap spark switch need to be studied.First,to study the arc formation process in slow discharge mode,the main electrode diameter 125 mm ball gap spark switch and controlled trigger circuit were designed.The ball gap spark switch is triggered to discharge test,and the discharge process of the ball gap spark switch is filmed with a high-speed camera,and the discharge characteristics are analyzed according to the test data.Secondly,the effects of trigger electrode diameter,relative position of trigger electrode and ground electrode,trigger pulse energy and trigger gap on the lower limit of operating voltage of the ball gap spark switch were studied.The effect of the main gap distance on the natural breakdown voltage and trigger breakdown voltage of the ball gap spark switch was also studied experimentally,and the electrode spacing,upper limit of operating voltage(natural breakdown)and lower limit of operating voltage(trigger breakdown)for the maximum voltage operating range of the 125 mm diameter ball gap spark switch were obtained.A two-parameter Weibull distribution was used to fit the experimental data to obtain the breakdown probability curves of the ball-gap spark switch at different main gap distances and the influence law of the trigger electrode on the operating voltage range.Finally,the simulation models of different sizes of ball gap switches are established according to the above ball gap spark switch structure,and the upper and lower working voltage limits and main gap distances of 150mm～300mm diameter ball gap spark switches at the maximum working voltage range are obtained by simulation in steps of 25 mm.The relationship between the ball diameter and the upper and lower operating voltage limits and the main clearance distance at the maximum operating voltage range is obtained by fitting.Combing arrester models and parameters,determine the arrester impact voltage residual voltage and rated frequency voltage,clearly give 110 k V,220 k V system,not grounded transformer neutral protection with48/109,55/132,55/140,60/144,72/186 and other models of surge arrester corresponding protection ball gap electrode diameter and main electrode spacing selection recommendations.