ABSTRACT
This chapter covers most of the on-line monitoring methods that are currently in use, including their benefits, system configurations, and application to the various operational parameters and accessories that can be monitored. Dissolved-gas-in-oil analysis of certain key gases has proved to be a valuable and reliable diagnostic technique for detection of incipient fault conditions not only within liquid-immersed transformers but also load tap changers (LTCs) and bushings. The time constants for migrations depend on the design of the transformer and the solid and liquid components in use. The combination of moisture, heat, and oxygen are the key conditions that lead to accelerated degradation of the cellulose. While LTCs represent the largest source of transformer failures, bushing failures represent a greater risk and cost in terms of damage and personal injury in vicinity of the transformer. Analysis of gases dissolved in the oil in the LTC compartment provides information as to the nature of an evolving problem within the LTC compartment.
