This paper presents theoretical and experimental
investigations of the onset voltage of conducting particle-initiated
negative corona in air insulated co-axial cylindrical
configurations. The conducting particles are spheres or wires of
varying dimensions. The particle is fixed either on the inner or
outer cylinder. The calculated onset voltage of negative corona is
based on the criterion developed for the formation of repetitive
negative corona Trichel pulses. This calls at first for an accurate
calculation of the electric field in the vicinity of the particle. The
investigated gap in the presence of particle is a three-dimensional
field problem, due to the asymmetric position of particle inside the
gap. The electric field is calculated using the charge simulation
technique with a new charge distribution. The effect of varying
field nonuniformity, particle shape, size and position on negative
corona onset voltage is investigated. Laboratory measurements of
negative corona onset voltage as influenced by particle position,
shape and dimensions in air insulated co-axial configurations are
carried out and compared with the present calculations. The
calculated values agreed well with those measured experimentally.