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.