Onset potential for unipolar charge injection

The unipolar charge injection model is split into a charge development region and a charge injection region. It is assumed that some potential drop V_i across the development region is necessary to create charges in this region. Once the potential is reached, the charges generated are injected into the injection region. The unipolar charge injection equation is modified to account for V _i, and it is shown that V_i is equivalent to the onset potential V_o in a gas corona. The results suggest that corona from a wire can be modeled as a lossy switch connected to one or more nonlinear resistors. The switch closes at the onset potential and always drops the onset potential across it. The resistors start out ohmic, but a little above the onset value they become nonlinear. Corona wires injecting positive ions into air indicated that the ion-to-neutral excess momentum ratio in this gas is near 10^-5. The equation considered suggests that in the charge injection region the resistance is linearly related to the length of the injection region