A space-charge life model for ac electrical aging of polymers

Contributed Review: Review of thermal methods for space charge measurement

“…[1][2][3][4] Due to the relevance of the space charge because of its negative effects, over the last decade the methods for space charge measurement in the field of insulation system diagnostics have acquired great interest and have been widely studied and improved. Thus, in order to overcome the challenges related to this phenomenon, many research groups have been interested in the physics of this phenomenon both in the past years [5][6][7][8][9] and in recent years. [10][11][12] In particular, many nondestructive methods for the characterization of dielectrics materials from the viewpoint of space charge accumulation have been developed.…”

Material morphology and energy barriers to electrical ageing

“…The moieties associated with this kind of ageing process are unlikely to be those deep in crystalline parts of the polymer, since these will be subject to the largest activation energies for a process of this type. It has been found, however, that the energy barriers in the DMM model have very similar magnitudes for different materials [2], and this implies that the chemical composition of the polymer does not make an appreciable difference to the activation energies involved in the ageing process. This is unlikely to be the case if it is moieties in the amorphous region that are important, since the morphology of these regions, and hence the barrier distribution to conformational rearrangement, will depend very strongly on the constituent molecule.…”

“…In the AC case, H dk and S d distributions were obtained separately; H dk was kept constant while the S d values were obtained and vice versa. In the DC case S d was assumed to be zero [2], and only the H dk distribution was investigated. …”

“…Various theories of electro-thermal ageing of high voltage polymeric insulation have been proposed recently, L. A Dissado et al [1], G. Mazzanti et al [2], T. J. Lewis et al [3], J. P. Crine [4], all of which can successfully fit experimental lifetime data, Griffiths et al [5]. However, each model predicts one single time to failure for a set of identical specimens subject to the same electrical field, E, and temperature, T except as discussed in L. A. Dissado et al [6].…”

“…In reality, this is not the case; a distribution of breakdown times is observed. Prediction of this distribution is attempted in this investigation, by a distribution of activation energy parameters within the Dissado-Montanari-Mazzanti (DMM) lifetime model [1], [2]. Investigation of the form of the parameter distributions, and how they change with field and temperature, then gives some insight into the ageing process.…”