IEC TR 61464:1998 pdf download – lnsulated bushings – Guide for the interpretation of dissolved gasanalysis (DGA) in bushings where oil is the impregnating medium of the main insulation(generally paper)

IEC TR 61464:1998 pdf download – lnsulated bushings – Guide for the interpretation of dissolved gasanalysis (DGA) in bushings where oil is the impregnating medium of the main insulation(generally paper).
This technical report gives guidance for the Interpretation of dissolved gas analysis (DGA)
which has been developed for bushings, in service, where the main insulation (generally paper)
is impregnated with mineral insulating oil according to IEC 60296.
This technical report is applicable to oil-filled and impregnated paper bushings in service.
Until further experience has been gained, the methods should be applied with caution in relation to other materials, e.g. synthetic hydrocarbons based on dodecylbenzene, according to IEC 60867.
The indication obtained by the interpretation of a dissolved gas analysis of an oil sample taken out of a bushing should be viewed as a guide and any resulting action should be undertaken with proper engineering judgement.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of this technical report. At the time of publication, the editions indicated were valid. All normative documents are subject to revision and parties to agreements based on this technical report are encouraged to investigate the possibility ol applying the most recent editions of the normative documents listed below Members of lEG and ISO maintain registers of currently valid International Standards.
lEG 60137:1995, Insulated bushings icr alternating voltages above 1 000 V
IEC 60296:1982, Specification for unused mineral insulating oils for transformers and switch gear
IEC 60567:1992, Guide for the sampling of gases and ci oil from oil-filled electrical equipment and for the analysis of free and dissolved gases
IEC 60599:1978, Interpretation of the analysis of gases in transformers and other oil-filled electrical equipment in service 1)
IEC 60867:1993, Insulating liquids — Specifications for unused liquids based on synthetic aromatic hydrocarbons
3 Interpretation of results of dissolved gas analysis (DGA) of oil-impregnated bushings
3.1 Gases generated from the decomposition of oil and paper
In normal operation conductor losses and electrical stress produce gases rum U’e decomposition of oil and paper. Thermal decomposition of oil and paper at moderate temperatures may also produce gases. The gases produced by the decomposition of the oil under normal operating conditions are hydrogen (H1), methane (CH4). ethane (C1He) and ethylene (C1H4). The gases produced by the decomposition of the cellulosic material are carbon monoxide (CO) and carbon dioxide (GO1).
The main causes ol abnormal gas generation within bushings in service, are thermal and electrical defects.
Under fault conditions, the above-mentioned gases, which are produced under normal operation, are generated at a higher concentration level. In addition to these, the gas acetylene (C2H2) may be produced
As the fault intensity increases the percentage concentrations of unsaturated hydrocarbons (chiefly C2H4 and C2H2) increase,
For faults involving cellulosic material, the key gases produced are carbon monoxide (CO) and carbon dioxide (GO3). As the thermal fault intensity increases, the percentage concentrations Of CO and CO1 may increase.
The diagnosis to determine the state of the bushing is based on the types of gases and gas concentrations generated by decomposition of oil and paper under normal ageing and various fault conditions and ratios of the gas concentrations.
The characteristic gases generated defined as key gases are categorized in table I together with the range of faults occurring in bushings.
The hydrocarbons quoted are those most commonly used in dissolved gas analysis. C hydrocarbons and C4 hydrocarbons are also formed but were not included in the database from which this report was produced.