Life expectancy of high voltage bushings based on incipient failure detections: a practical approach

Failures in HV bushings are responsible for the third part of major failures in HV power transformers and reactors, according to data available in different researches. Sometimes, bushing failures could have not impact as mayor failures and, as a consequence, these events are both, not registered nor taken into account to develop statistics. Detection of incipient failures sometimes are not neither registered. It results relevant to know the HV bushings life expectancy in order to define proactive actions with time enough before a major failure could occur as well as to prioritize the purchase of spare bushings for each model. In this work, criteria to recognize incipient failures in HV bushings is proposed. This is based on our own experience with field results of dissipation factor and capacitance measurements, tip-up test and frequency domain spectroscopy measurements over a population of more than 1000 HV bushings. Such criteria are compared against the existing ones in available bibliography. The life expectancy of HV bushings according with each method used are evaluated and compared every each other looking for if exists one of them which detect problems in an earlier way.