IEC 62975-2021 pdf free download – Natural esters – Guidelines for maintenance and use in electrical equipment.
7Evaluation of natural ester in equipment in service
7.1General
A natural ester in service is subjected to heat, oxygen, water and other catalysts,all of whichare detrimental to the properties of all insulation. In order to maintain the quality of the naturalester in service,regular sampling and analysis shall be performed.
From an environmental point of view，visual inspection can also be used to monitor leakageand spills of natural esters.
ln case of leakage, natural esters are very prone to be oxidized, much faster than mineral oilforming thin films that are difficult to clean if not done in a short time.
Often the first sign of natural ester deterioration may be obtained by direct observation of thenatural ester clarity and colour through the sight glass of the conservator or sight glass of theBuchholz relay.
The interpretation of results, in terms of the functional deterioration of the natural ester, shallbe performed by experienced personnel based on the following elements of risk managementand life cycle management:
.characteristic values for the type and family of natural ester and equipment, developed by
statistical methods;
evaluation of trends and the rate of variation of the values for a given natural esterproperty;
typical values, for “good”,”fair””and “poor”for the appropriate type and family ofequipment as are given in Table 5.
Application of naturalester liquids in power transformers is recommended for sealedequipment only and at this time is still relatively limited compared to mineral oil. The collection
of operating data (approximately 35 000 records) from a very large, but young. population oftransformers contributed to the development of this document. The recommended valuesproposed in this document shall be used carefully. Manufacturers of natural ester liquidsshould be contacted in case of specific questions or concerns.
7.2 Frequency of examination
lt is impossible to lay down a general rule for the frequency of examination of natural esters inservice which will be applicable to all possible situations that might be encountered.
The optimum frequency will depend on the type，function，voltage，power，construction andservice conditions of the equipment,as well as the condition of the natural esters asdetermined in the previous analysis. A compromise will often have to be found betweeneconomic factors and reliability requirements.
Much greater difficulties exist in deciding frequency of testing and permissible natural esterdeterioration levels which are acceptable for all applications of insulating liquids in relation to
differences in operating policies，reliability requirements and types of electricalsystem. Forexample,large power companies may find the full application of these recommendations todistribution transformers uneconomical. Conversely,the industrialuser，whose activitiesdepend on the reliability of his power supply，may wish to institute more frequent and strictercontrols of liquids dielectric quality as a means of guarding against power failures.
By way of a guide, a suggested frequency of tests suitable for different types of equipment is given in Table 4 but,less frequent testing may be appropriate based on life cycle analysis(LCA) and/or life cycle management(LCM) and risk assessment (RA).
Generally，check measurements shall be carried out on the basis of the following criteria,which apply to natural esters as other transformer dielectric liquids.
a) Characteristics may be tested periodically, at intervals as suggested in Table 4,unless otherwise defined.
b) The frequency of examination may be increased where any of the significant properties
indicates that the liquid is in fair or poor condition，or when trend analysis ‘indicatessignificant changes.
c)The degradation of the natural ester will accelerate with increased temperature and in the
presence of oxygen (oxidation) and water (hydrolysis). Therefore,heavily loadedtransformers may need more frequent liquid-sampling ‘and complementarytesting. As aconsequence,the use of natural esters is recommended only for equipment that are notopen to the atmosphere.IEC 62975 pdf download.