Post by HAEFELY AG

1964: The Hidden Dynamics Behind an AC Flashover This photograph from 1964 captures a controlled AC flashover generated by a 1’000 kV, 1 A test transformer cascade. The wire visible at the top electrode was intentionally installed to increase the local electric field strength and initiate the discharge at a defined location. It also generates the streamers visible in the image. At first glance, this appears to be a single flashover. In reality, an AC flashover behaves very differently from a DC flashover. With DC voltage, a flashover typically occurs once as the insulation breaks down and a conductive path is established. With AC voltage, the situation is different. As the voltage continuously changes polarity, the discharge extinguishes and reignites repeatedly. During each cycle, the flashover develops again, creating the characteristic appearance captured in this long-exposure photograph. What looks like a single event is actually the result of many individual discharge processes occurring in rapid succession. Images like this provide a fascinating insight into the physics of high-voltage testing and remind us that behind every test result lies a complex interaction between electric fields, insulation systems, and the surrounding air. And just as this history stretches back more than a century, our commitment remains the same: to continue supporting high-voltage testing laboratories for many decades to come. HAEFELY AG member of the PFIFFNER Group: PFIFFNER Group - PFIFFNER Deutschland GmbH - PFIFFNER do Brasil - Pfiffner Transformatör AŞ - MGC Moser-Glaser AG - Haveco AG