Transmission and distribution operators throughout the world control significant populations of ageing large transformers which use mineral oil and paper as the dielectric insulation. Some of these transformers are reaching the end of the projected service life and subject to various end-of-life failures which cause the transformer to be taken out of service.
One failure mode, for which no root cause has been identified, occurs in the inter-phase barrier region. This is the mechanical space between the high voltage series coils in the transformer. This failure mode leaves evidence of surface tracking along the inter-phase barrier boards.
This project is supported by UK National Grid and has the principle goal of understanding this failure mode with a secondary goal of early life failure prevention. The project has twin themes of high voltage engineering and dielectric ageing.
This is an experimentally based project and has resulted in a unique experimental apparatus to be developed. The apparatus permits high voltages from two separate voltage sources to be applied to a scale model of inter-phase barrier boards under controlled conditions of moisture and temperature. The voltage sources can be controlled independently of each other in terms of amplitude and phase.
The development of the apparatus, along with some novel side experiments is revealing some interesting properties of surface tracking on pressboard insulation. The results from this study should help transmission and distribution operators in long term asset management.