Biodegradable Esters – Aspects of Applicability Criteria Determination
Electrical insulating system of power transformers, which is not limiting for their performance in terms of power, is based on the combination of liquid and solid dielectrics. Solid part is kind of absorbing material usually cellulose based. Traditional systems commonly use as the liquid component mineral oil which has excellent electrical and physical properties. In the same time it has one significant disadvantage which is intolerance to the environment - eventual contamination. In keeping with the current trend of respecting the quality of the environment is therefore necessary to look for new electrical insulating liquids. It should be easy biodegradable and have excellent electrical and physical properties at least at the level of mineral oils. These new liquids have mostly ester character. Their properties are necessary to standardize, determine and set the mandatory levels of monitored parameters. Presented criteria are based on current standards and are verified by carried out experiments. Establishment of criteria is based on the grade of electrical insulating liquids according to relevant standards and regulations, taking into account the proper division of transformers by voltage and transmitted power. Electro insulating systems of these machines are by their nature and characteristics relevant to a given voltage levels and transmitted power. The determination of applicability requires identification of basic degradation mechanisms, especially the effect of temperature by setting criterion for temperature aging in relation to international standards. It is possible to study and compare standardized and newly evaluated parameters. In the case of similar features of ester and mineral fluids, standards for mineral fluids can be employed. The closest to reality is of course the establishing of aging criteria evaluated by experiment and by determination of the lifetime curve of studied electrical insulating liquids. Important is the water content and its criterion determination, while it is a known fact that natural esters achieve substantially higher values of dissolved water than used mineral oils. It is therefore advantageous to determine the water content in solid part (paper) of insulation by using of TDS or FDS method. The paper shows possible approaches for determining the values of criterion for new types of insulating liquids. It used a combination of methods for determining the values of individual parameters and proposed values of till now unspecified parameters. It is also important to express the difference between new and commonly used electrical insulating liquids of mineral character.