Behavior of Air Insulating GAPS of DC Systems Under Impulse, DC and Composite Voltages

This paper deals with the behavior of air insulating gaps of direct current (dc) transmission systems in the voltage range of ±600 kV to ±1 200 kV. The gaps studied were simulating either a bipolar dc tower or a bipolar rigid bus system. The influence of the terminations of the two ends of the insulator supporting the bus was investigated by using a single bus supported at one end. The breakdown voltage of the gaps was determined for a pure impulse, pure dc voltage or composite voltage formed by a dc on which an impulse was superimposed. The proximity effect of one pole on the pole-to-ground breakdown voltage of the other was also investigated.