Arrester-current based on-line MOSA condition assessment using a new approach

The degradation of metal oxide surge arresters may be detected by consideration of the resistive component of arrester current. In order to obtain this component, accurate knowledge of the voltage is essential which is difficult in practice. To get around this difficulty a probe-based method was devised in the late eighties and an instrument developed based on that method. In this method the third harmonic component of the resistive current is computed and used as a diagnostic tool. The errors associated with this method have been found to be due to probe positioning and the presence of voltage harmonics.; An alternative and simpler software-based iterative method of obtaining the resistive component has been suggested in literature which relies on the fact that the phase shift between the resistive and capacitive components of arrester current is constant; knowledge of the applied voltage is not required to implement this method. Furthermore, this method does not rely on information gathered from probes and is therefore free of probe related errors. Also, it is claimed that the influence of voltage harmonics is relatively small.; In this thesis, the phase shift criterion has been verified and utilized but in a different manner to obtain the resistive current. The results are compared with the Compensation Technique (Bench Mark Method). (Abstract shortened by UMI.)...