ABSTRACT
The initial effect of a high-voltage (HV), high-frequency (HF) transient on insulation is to produce a mechanical shock wave in the insulation. This mechanical shock wave will produce a vibration that compresses and expands the insulating material. In practice, and given the dimensions of the lines, the connections between circuit breakers and current transformers (CT), and the physical dimensions of the CT itself and its pedestal, the stepped wave is transformed into a spike with a minimum fall time of 0.3 µs. The wave enters the dielectric through the HV head as conduction current and voltage. It passes through the HV Faraday screening and is converted into a displacement current and electric field to cross the dielectric material and reach the low-voltage electrode. An analysis is required of the length and width of the insulating bushing to ensure that it behaves as a short transmission line from the point of view of the HV, HF transients that are applied.
