Fundamental investigation of microsecond breakdown near a high permittivity dielectric

A 3 microsecond risetime, 300 μs fall time, 25 kV high voltage pulse, chosen to emulate lightning discharges is used to investigate breakdown in close proximity to a high permittivity rutile dielectric (E
_r
~ 100) cylinder with 1 cm diameter. A needle-plane electrode structure is utilized with 1.05 cm electrode separation. The dielectric location is varied from immediately under the needle, to more than a 1 cm away from the needle axis. Basic system design and simulation are presented, along with simulations of the electric field distribution for various dielectric locations. The dependence of breakdown voltage on dielectric proximity is presented in detail. For instance, a minimum in breakdown voltage is observed when the dielectric cylinder is placed slightly off-center from the needle’s center axis. Using high speed imaging, discharge inception and growth are presented with ~10 ns resolution.