IEEE Std C57.155 pdf free download
IEEE Std C57.155 pdf free download.Interpretation of Gases Generated in Natural Ester and Synthetic Ester-Immersed Transformers.
Synthetic ester insulating liquids have been primarily used as a less flammable liquid substitute in specialty transformer applications since the early 1980s. Natural ester insulating liquids were first used with small distribution transformers in the late I 990s and were introduced for use in power transformers in 2001. With an increasing population of ester-immersed transformers, there is an increasing need for a specific guide to the dissolved gas analysis (DGA) of these liquids.
It is best when a large number of field observations can be used as the basis for defining a normally operating transformer. As yet, there have not been enough failures of ester-immersed transformers to clearly define characteristic transformer faults or risk of failure, so laboratory data is used to provide indication of normal operation, failure conditions, and trending along with a comparison to mineral oils.
The value of DGA derives from the fact that certain gases arc produced by the abnormal release of thermal and/or electrical energy into liquid-immersed equipment. Analysis of the dissolved gas is used to indicate the type of fault. Determination of the rates of gas production is used to indicate the severity of the fault.
The differences between an ester liquid and mineral oil are far greater than the differences between any two mineral oils. Fortunately, the gases generated in ester liquids under fault conditions are the same as those that are generated in mineral oil. However, the ratios and rates of generation can be very different. This at least allows for the use of common methods for sampling and testing.
The differences in the chemical structure of ester liquids leads to important differences in how some gases are produced. Gases produced by these different processes give new or additional meaning to the possible interpretation of DGA results. This means that a common method for interpretation of mineral oils data will not work as reliably for ester liquids. Modifications to interpretative methods for mineral oils arc necessary for their use with ester fluids.
The most significant differences in gas production for ester fluids arc as follows:
— Ethane produced from non-fault conditions for ester fluids containing linolenic acid
— Methane, ethane, and ethylene produced in greater amounts and at lower temperatures from overheating
— Methane, ethane, and ethylene produced in different proportions than mineral oil from overheating Carbon dioxide and carbon monoxide produced abundantly from overheating of the ester liquid causes of gas formation
As with mineral oil insulating liquids, the fundamental steps of the decomposition of esters involves the breaking of carbon—hydrogen and carbon—carbon bonds. Active hydrogen and hydrocarbon fragments, called “free radicals” are formed. These free radicals can combine with each other to form gases, molecular hydrogen (H2), methane (CH4), ethane (C2H6), etc., or they can recombine to form new, condensable molecules. Further decomposition and rearrangement processes lead to the formation of products such as ethylene and acetylene and, in the extreme, to modestly hydrogenated carbon in particulate form.IEEE Std C57.155 pdf download.
