Space charges of different mobilities: A novel data processing method

A new way to process the information obtained in space‐charge distribution measurements is presented. It is applied to data given by the pressure wave propagation method. This method can be carried out with or without an applied voltage. It is shown however that it does not always allow, under dc stress, for quantitative evaluation of the charge density, if the material contains space charges of very different mobilities, and particularly of high mobility. The new processing technique described here overcomes this difficulty. It is illustrated by application to cross‐linked polyethylene samples. This permits the discrimination of two different kinds of space charge. One is the normal space charge which has been reported many times, the second is a type that displays a high mobility. This charge is not directly visible even at very short times after the suppression of the applied voltage. In these measurements, this very mobile space‐charge is always seen as heterocharge near the anode.