Sacrificial coatings for improved detection of overheating in generators

Ion chamber monitors are now routinely used as on-line detectors for the presence of thermally produced particulates. In order for the particulates to appear, the surface temperature of the polymeric materials that are most commonly used in generators must exceed 200°C. The higher voltage ratings of the large generator units being built for central station application means that the organic polymeric materials used as insulation are thicker and a larger temperature difference can exist between the inner and outer surfaces. Sacrificial coating systems capable of thermal particulation at a lower temperature than these common generator materials would provide an earlier indication of overheating, thereby enhancing the importance of the ion chamber monitors. The requirements for such a sacrificial coating and several families of compounds that have been investigated for use as sacrificial coatings will be described.