| Available from UMI in association with The British Library.; Investigations of surge overvoltage mitigation and protection are described. These are corona discharge effects and the use of non-linear zinc oxide elements in surge arresters.; A corona model that can be readily incorporated in insulation coordination design procedures taking into account line conductor geometry, impulse polarity and waveshape is required. Such a model has been developed in this work which is based upon well known impulse corona properties. The model prediction is successfully applied to coaxial, conductor-plane and twin-conductor geometries, and with the generalised form obtained, may be equally well applied to more complex systems. Using the biased field filter technique, the modification of the impulse field at a line conductor (single and twin) under corona conditions is investigated. It is shown that during the corona discharge, the field is maintained just below the minimum inception field calculated from empirical formula which is employed in the corona model.; Under power frequency, oscillatory and switching overvoltages, corona discharge persists well beyond voltage peak. A corona extinction criterion is introduced which can be used for corona dynamic modelling under these conditions. It is applied here in conjunction with 50 Hz corona discharge test data obtained from a new biased double electrode system. This has provided a complete budget of the space charge behaviour under the conditions studied the charge injected by the corona electrode, the charge collected by the passive electrode and the charge in the inter-electrode space. The modelling procedures applied also enable two stages of the discharge to be identified.; The application of the field filter measurement technique is extended to develop a new double electrode test cell for testing and assessing the quality of non-linear zinc oxide surge arrester elements and linear solid insulating materials. This has provided data on ZnO behaviour in the leakage current region which is not obtained by conventional voltage-current tests. The static characteristic of the cell is determined by digital computation. The leakage properties of zinc oxide test samples are studied using the test cell. The test results are also used to determine the effective dielectric thickness of the test samples which differs significantly from the geometrical thickness. (Abstract shortened by UMI.)... |
