Flashover Characteristics and Insulation Coordination of Phase-to-phase Air-gaps for AC Transmission Line With 1 000 kV Double-circuit and 500 kV Double-circuit on the Same Tower

In order to ensure the reliability and economy of phase-to-phase air-gaps design,in this paper,based on the tower structure and conductor arrangement of the transmission line with 1 000 kV double-circuit and 500 kV double-circuit on the same tower,phase-to-phase air-gaps flashover tests were carried out.The air-gaps tests include 1 000 kV conductor to 1 000 kV conductor,1000 kV conductor to 500 kV conductor,and 500 kV conductor to 500 kV conductor.Different wave-front impulse voltage was generated with two long-front impulse voltage generators to simulate phase-to-phase switching over-voltage surge of the transmission line.By different conductor structure and different wave-front time tests,a large number of test data and several important flashover characteristics curves were obtained.According to the phase-to-phase over-voltage level of one planning UHVAC power project——-Suzhou-to-Huxi transmission line in East China,the phase-to-phase insulation gaps were analyzed and given out.Results show that average gap factor K of 8-subconductor bundle phase-to-phase flashover voltage under 1 000 ?s long-front switching impulse is 1.61,and K of 8-subconductor bundle to 4-subconductor bundle and 4-subconductor bundle to 4-subconductor bundle under standard switching impulse are respectively 1.44 and 1.49.It provides external insulation design basis for the power transmission mode with ultra high voltage(UHV) and extra high voltage(EHV) lines on the same tower,first presented to the international.