Dissolved Gas Analysis, DGA, is based on the fact that the release of energy in oil filled electrical equipment results in a partial destruction of insulating fluids and/or solid insulation. The number of molecules destroyed is relatively small but detectable amounts of low molecular weight gases are produced. The quantification of the low molecular weight “fault gases” is the basis of all DGA.

Changes in the way utilities manage their transmission and distribution assets, as well as increases in peak load demand, has led to the need to subject more and more substation transformers to overload conditions. This paper will present the concept of utilizing a high temperature insulation system, also called a hybrid insulation system, as a way for enhancing the performance and load capability during the transformer repair process.

Thermal and electrical faults dissipate energy. If dielectric fluid or solid insulation is in the vicinity of a fault, energy transfer will occur and this will result in non-reversible partial molecular degradation of insulating materials. The existence of irreversibly generated decomposition products is the basis for dissolved gas analysis (DGA)1. These processes are not limited to transformers and can occur in any oil filled electrical equipment. The application of DGA to transformers has been universally accepted as a valuable diagnostic tool. When consideration is taken of the operating parameters of Load Tap Changers and Oil Circuit Breakers, there is no reason why the DGA methodology cannot be applied in a cost-effective preventive maintenance program.

The new deregulated electric utility environment is driving Transmission and Distribution companies to find ways to improve their competitive position. Maximizing return on investment (ROI) is often a key financial driver when formulating a profitable T D operation and maintenance strategy. Increased equipment utilization, deferred capital expenditure and reduced maintenance expense are all a part of the guidelines for today’s T D asset strategists and managers. Although tighter operating budgets and reduced spending are nothing new to utility engineers and planners, today’s increased need to leverage more out of existing equipment must be achieved with the majority of T D assets nearing the end of their life cycle.

It has been well over thirty years since dissolved gas analysis, DGA, was introduced as a diagnostic tool for monitoring mineral oil filled transformers. It is now universally accepted as the method of choice to locate incipient thermal and electrical faults. DGA methodology and applicability have evolved significantly since its inception. The evolutionary development includes new laboratory methods, on-line DGA, application to additional types of fluid filled equipment, application to dielectric fluids other than mineral oil and new diagnostic interpretation protocols.

In today’s world of deregulated electric utilities, the concepts of transformer life extension, increased loading, and reduced maintenance are often discussed. These ideas at first appear to be contradictory in nature, but all strive for the same results; reduced operating costs and improved reliability in the delivery of electricity. In fact, for substation transformers, all of these goals can be obtained with the implementation of a strategic “Life Cycle Management Program”. This paper addresses the primary concepts of life extension and increased loading of transformers, and how these issues are interrelated.

During the past forty years, dissolved gas analysis DGA, has become universally accepted as the premier diagnostic tool for location of incipient faults in transformers. Extension of DGA to other oil filled equipment were proposed and debated during the past decade. The consensus opinion was that gases developed during the switching operation would “cover up” any gases due to equipment problems. Table 1 shows the gas producing processes that occur in oil filled electrical apparatus. The gases that are produced by these various processes are listed in Table II. Recognition of these differences between normal and abnormal gassing conditions paved the way to diagnostic evaluation of load tap changers LTC’s, and oil filled circuit breakers, OCB’s.

During the B.D. era, before deregulation, run to failure, time based and operation count based maintenance methods were widely employed. These methods were effective in maintaining the power delivery system but were labor intensive and not cost effective. Time based and operation count based maintenance methods could not identify units that developed problems between scheduled inspections. Units were often inspected on a time basis and no problems were identified.

Fluids, liquids or gases, that are used in electrical equipment serve three essential purposes. These fluids must provide adequate insulation, efficiently transfer heat from the source to the atmosphere and quench arcs that may develop in the equipment. To meet these requirements the selected fluid must consist of non-polar molecules that are chemically stable. Viscosity, specific heat and thermal conductivity are properties that must also be considered when evaluating the ability of the fluid to conduct heat.

New rules in the deregulated electric utility business require Transmission and Distribution companies to find ways to improve their competitive position. Maximizing return on investment (ROI) is often a key financial driver when formulating a profitable operating T D strategy. Increased equipment utilization, deferred capital expenditure and reduced maintenance expense are all a part of the guidelines for today’s T D asset strategists and managers. Although tighter operating budgets and reduced spending are nothing new to utility engineers and planners, today’s increased need to leverage more out of existing equipment must be achieved with an aged asset base.