Comparison of methods for determining corona inception voltages of transmission line conductors

Corona inception voltages are important parameters for power transmission-line conductors. However, there is no specific criterion for the determination of the corona inception voltage on such conductors. A corona cage is an effective and economical means for testing transmission-line conductors as it allows the duplication of surface electric fields, and hence the corona phenomena, at lower conductor voltages. Measurements with an ultraviolet imager, a partial discharge detector, a current-measuring radio-frequency interference receiver, and a sound level meter were used to observe the transition region between no corona and strong corona and hence determine the corona inception voltages of two practical conductors, types LGJ500/35 and LGJ400/50. Good agreement was found between the four approaches. The corona inception voltage was also calculated from first principles after determining the electric field near the surface strands using a charge simulation method, and compared with the peak inception voltages found from the measurements. Comparison was also made with the values obtained be applying Peek's equation. In both the calculations, Peek's surface roughness factor ‘m’ was applied with a value of 0.81 giving close agreement with the measurements.