IEEE Std C57.147 pdf free download
IEEE Std C57.147 pdf free download.Acceptance and Maintenance of Natural Ester Insulating Liquid in Transformers.
Mineral Oil Insulating Liquids: Natural ester insulating liquids are typically miscible and compatible with mineral oil insulating liquids, as well as with halogenated hydrocarbon insulating liquids. Mixing unused insulating natural esters with mineral oil may or may not significantly impact their typical property values or impact performance. For the property values that do change, the change may or may not be proportional to the ratio of the content of the liquids. See B.3 for additional details.
NOTE—If the purpose of using a natural ester liquid is to comply with Article 450.23 of the National Electrical Code® (NEC®) (NFPA 70®, 2017 Edition), (for example, to use a transformer indoors without a vault), that article requires that less-flammable transformer liquids have an ASTM D92 fire point of not less than 300 °C and that the installation complies with all restrictions provided for in the product listing of the liquid (see Article 100 of the 2017 NEC). Also, too much mineral oil contamination in a natural ester may impact meeting the requirements of the National Electrical Safety Code® (NESC®) (Accredited Standards Committee C2). Contact the natural ester manufacturer to determine the maximum mineral oil content range to prevent the open cup fire point from dropping below the 300C minimum requirement. Typically a maximum of 7% mineral oil contamination is acceptable.
Less and Non-Flammable Insulating Liquids: Although in many cases different types of less-flammable liquids [e.g., synthetic esters, synthetic hydrocarbons, and high molecular weight hydrocarbons (HMWHs)] are miscible, such mixtures should generally be avoided in transformers and liquid processing equipment as practical, unless such mixtures are done purposely for certain applications or to achieve certain properties. Silicone insulating liquids are typically not miscible with natural ester dielectric liquids, so any cross contamination should be avoided. Typically natural esters are miscible with non-flammable halogenated hydrocarbon insulating liquids, such as polychlorinated biphenyls (PCBs). Although natural esters would not normally be mixed with halogenated hydrocarbons, this could occur after retrofilling older transformers containing such insulating liquids. Consult with the manufacturer of each insulating liquid for advice ifmixing has occurred in situ inadvertently or purposefully.
The acid (neutralization) number for unused and service-aged insulating liquids is, in general, a measure of the amount of acidic constituents in the liquid. The formation of acidic components is commonly associated with oxidation of mineral oil. The acidic components formed from mineral oil are considered undesirable as they can contribute to solid insulation aging and sludge formation. The acid number has been used as a general guide for determining when mineral oil should be replaced or reclaimed.
In natural ester liquids, acidic components arise from diverse processes and may not be associated with adverse effects. The source of these components, as well as their magnitude, should be considered when determining what action should be taken. The acidic components are produced mainly from hydrolysis, pyrolysis, and oxidation of natural ester.
Hydrolysis of natural ester bonds releases fatty acids. The free fatty acids introduced by this process are long chain organic acids. Most of these acids are 18 carbons in length, CIK, while a few are 16 carbon sequences, C6. The strength of organic acids is inversely related to the chain length. Short chain acids such as acetic acid. C,, are strong and, in sufficient amount, can be detrimental to the condition of other materials in contact with the insulating liquid. Long chain acids such as stearic acid, C1, are weak and have not been associated with any detrimental effects. The presence of dissolved water in the liquid facilitates the hydrolysis reaction. It is common for the acid number to significantly increase during the first months of the transformer operation, attributable to the hydrolysis reaction with the initial moisture from the insulating paper.IEEE Std C57.147 pdf download.
