Experiment on Leader Propagation Characteristics of Air Gaps in UHVDC Transmission Towers Under Positive Switching Impulse Voltages

Rapid developments in EHV/UHV transmission systems require a deeper understanding of the mechanism of long air gap discharge.Leader propagation is one of the main processes in long gap breakdown.In this paper,the leader propagation characteristics of real size±800 kV UHVDC transmission tower gaps under positive switching impulse voltages(185/2290μs)are investigated.An integrated observation platform consisting of an impulse voltage divider,a coaxial shunt,a high-speed video camera,and a set of integrated optical electric field sensors(IOES),is established.The waveforms of impulse voltage,discharge current,electric field variation at specific positions,and time-resolved photographs of discharge morphology are recorded.Axial leader velocity and the relationship between leader advancements and injected charge are obtained.The typical value of leader stable propagation velocity is 1.7–2.2 cm/μs,which varies slightly with the gap length and applied voltage amplitude.The leader velocity in the re-illumination process is much higher,and is seen as varying from 5 cm/μs to 30 cm/μs,with an average value around 10 cm/μs.The charge in leader channel per unit length is 20–40μC/m,which illustrates a near-direct proportion relationship between discharge current and leader velocity.The observed parameters are important for further simulation of the tower gap breakdown processes.

Shanghai Tower

Owner:Shanghai Tower Construction & Development Co.,Ltd.Contractor:Shanghai Construction Group Co.,Ltd.Architectural Designer:Gensler,USA Structural engineer:Thornton Tomasetti,USA Construction Drawing Designer:Tongji Architectural Design(Group)Co.,Ltd.With a height of 632 m,the Shanghai Tower stands