Identification of the capacitance coefficients of multiphase transmission lines exhibiting corona under transient conditions

This theoretical paper identifies the different capacitance coefficients that can be defined for multiphase power transmission lines exhibiting corona under transient conditions. Equations are derived, allowing the evaluation of those coefficients on the basis of the space-charge distribution around the conductors. No restrictions are imposed on their radial distribution. Also no assumptions are made about the space-charge density evolution in time, therefore allowing consideration of corona dynamics due to both the space-charge generation dynamics and the space-charge drift. The derived equations can be used with any corona model able to evaluate the time behaviour of the space-charges, for given applied voltages. The expressions obtained for the multiphase corona capacitance coefficients show that these can be evaluated from single-phase test results. An illustration example is presented using a simplified corona model. Results show how corona on a given conductor affects all the multiphase capacitance coefficients