IEEE C57.104-2008 - IEEE Guide for the Interpretation of Gases Generated in Oil-Immersed Transformers.pdf

1、IEEE Std C57.104-2008(Revision ofIEEE Std C57.104-1991)IEEE Guide for the Interpretation ofGases Generated in Oil-ImmersedTransformersIEEE3 Park Avenue New York, NY 10016-5997, USA2 February 2009 IEEE Power 2) the use of fixed instruments for detecting and determining the quantity of combustible gas

2、es present in gas-blanketed equipment; 3) obtaining samples of gas and oil from the transformer for laboratory analysis; 4) laboratory methods for analyzing the gas blanket and the gases extracted from the oil; and 5) interpreting the results in terms of transformer serviceability. The intent is to

3、provide the operator with useful information concerning the serviceability of the equipment. An extensive bibliography on gas evolution, detection, and interpretation is included. Keywords: gas analysis, oil, oil-filled transformers, transformers The Institute of Electrical and Electronics Engineers

4、, Inc. 3 Park Avenue, New York, NY 10016-5997, USA Copyright 2009 by the Institute of Electrical and Electronics Engineers, Inc. All rights reserved. Published 2 February 2009. Printed in the United States of America. IEEE is a registered trademark in the U.S. Patent +1 978 750 8400. Permission to p

5、hotocopy portions of any individual standard for educational classroom use can also be obtained through the Copyright Clearance Center. iv Copyright 2009 IEEE. All rights reserved. Introduction This introduction is not part of IEEE Std C57.104-2008, IEEE Guide for the Interpretation of Gases Generat

6、ed in Oil-Immersed Transformers. IEEE Std C57.104-1991 was officially withdrawn by IEEE based on recommendation by the Transformers Committee of the IEEE Power solubility and degree of saturation of various gases in oil; the type of oil preservation system; the type and rate of oil circulation; the

7、kinds of material in contact with the fault; and finally, variables associated with the sampling and measuring procedures themselves. Because of the variability of acceptable gas limits and the significance of various gases and generation rates, a consensus is difficult to obtain. The principal obst

8、acle in the development of fault interpretation as an exact science is the lack of positive correlation of the fault-identifying gases with faults found in actual transformers. The result of various ASTM testing round-robins indicates that the analytical procedures for gas analysis are difficult, ha

9、ve poor precision, and can be wildly inaccurate, especially between laboratories. A replicate analysis confirming a diagnosis should be made before taking any major action. This guide is intended to provide guidance on specific methods and procedures that may assist the transformer operator in decid

10、ing on the status and continued operation of a transformer that exhibits combustible gas formation. However, operators must be cautioned that, although the physical reasons for gas formation have a firm technical basis, interpretation of that data in terms of the specific cause or causes is not an e

11、xact science, but it is the result of empirical evidence from which rules for interpretation have been derived. Hence, exact causes or conditions within transformers may not be inferred from the various procedures. The continued application of the rules and limits in this guide, accompanied by actua

12、l confirmation of the causes of gas formation, will result in continued refinement and improvement in the correlation of the rules and limits for interpretation. Individual experience with this guide will assist the operators in determining the best procedure, or combination of procedures, for each

13、specific case. Some of the factors involved in the decision of the operator are: the type of oil preservation system, the type and frequency of the sampling program, and the analytical facilities available. However, whether used separately or as complements to one another, the procedures disclosed i

14、n this guide all provide the operator with useful information concerning the serviceability of the equipment. 2. Normative references The following referenced documents are indispensable for the application of this document (i.e., they must be understood and used, so each referenced document is cite

15、d in text and its relationship to this document is explained). For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments or corrigenda) applies. ASTM D 923, Standard Practices for Sampling Electrical Insulati

16、ng Liquids.1ASTM D 2945, Standard Test Method for Gas Content of Insulating Oils. 1ASTM publications are available from the American Society for Testing and Materials, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, USA (http:/www.astm.org/). IEEE Std C57.104-2008 IEEE Guide for the Interpr

17、etation of Gases Generated in Oil-Immersed Transformers 3 Copyright 2009 IEEE. All rights reserved. ASTM D 3305, Standard Practice for Sampling Small Gas Volume in a Transformer. ASTM D 3612, Standard Test Method for Analysis of Gases Dissolved in Electrical Insulating Oil by Gas Chromatography. 3.

18、Definitions, acronyms, and abbreviations For the purposes of this guide, the following terms and definitions apply. The Authoritative Dictionary of IEEE Standards Terms should be referenced for terms not defined in this clause. 3.1 Definitions 3.1 key gases: Gases generated in oil-filled transformer

19、s that can be used for qualitative determination of fault types, based on which gases are typical or predominant at various temperatures. 3.2 partial discharge: An electric discharge that only partially bridges the insulation between conductors, and that may or may not occur adjacent to a conductor.

20、 3.2 Acronyms and abbreviations TCG total combustible gas TDCG total dissolved combustible gas 4. General theory The two principal causes of gas formation within an operating transformer are thermal and electrical disturbances. Conductor losses due to loading produce gases from thermal decomposition

21、 of the associated oil and solid insulation. Gases are also produced from the decomposition of oil and insulation exposed to arc temperatures. Generally, where decomposition gases are formed principally by ionic bombardment, there is little or no heat associated with low-energy discharges and partia

22、l discharge. 4.1 Cellulosic decomposition The thermal decomposition of oil-impregnated cellulose insulation produces carbon oxides (CO, CO2) and some hydrogen or methane (H2, CH4) due to the oil (CO2is not a combustible gas). The rate at which they are produced depends exponentially on the temperatu

23、re and directly on the volume of material at that temperature. Because of the volume effect, a large, heated volume of insulation at moderate temperature will produce the same quantity of gas as a smaller volume at a higher temperature. 4.2 Oil decomposition Mineral transformer oils are mixtures of

24、many different hydrocarbon molecules, and the decomposition processes for these hydrocarbons in thermal or electrical faults are complex. The fundamental steps are the breaking of carbonhydrogen and carboncarbon bonds. Active hydrogen atoms and hydrocarbon fragments are formed. These free radicals c

25、an combine with each other to form gases, molecular hydrogen, methane, ethane, 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 hydrogena

26、ted carbon in particulate form. IEEE Std C57.104-2008 IEEE Guide for the Interpretation of Gases Generated in Oil-Immersed Transformers 4 Copyright 2009 IEEE. All rights reserved. These processes are dependent on the presence of individual hydrocarbons, on the distribution of energy and temperature

27、in the neighborhood of the fault, and on the time during which the oil is thermally or electrically stressed. These reactions occur stoichiometrically; therefore, the specific degradations of the transformer oil hydrocarbon ensembles and the fault conditions cannot be predicted reliably from chemica

28、l kinetic considerations. An alternative approach is to assume that all hydrocarbons in the oil are decomposed into the same products and that each product is in equilibrium with all the others. Thermodynamic models permit calculation of the partial pressure of each gaseous product as a function of

29、temperature, using known equilibrium constants for the relevant decomposition reactions. An example of the results of this approach is shown in Figure 1 due to Halstead. The quantity of hydrogen formed is relatively high and insensitive to temperature; formation of acetylene becomes appreciable only

30、 at temperatures nearing 1000 C. -7-5-3-11351725 1225 725 225Temperature Deg. CLOGConcentration(PartialPressure)N/M2CH4H2C2H6C2H2C2H4Figure 1 Halsteads thermal equilibrium partial pressures as a function of temperature Formation of methane, ethane, and ethylene each also have unique dependences on t

31、emperature in the model. The thermodynamic approach has limits; it must assume an idealized but nonexistent isothermal equilibrium in the region of a fault, and there is no provision for dealing with multiple faults in a transformer. However, the concentrations of the individual gases actually found

32、 in a transformer can be used directly or in ratios to estimate the thermal history of the oil in the transformer from a model and to adduce any past or potential faults on the unit. As the simplest example: the presence of acetylene suggests a high-temperature fault, perhaps an arc, has occurred in

33、 the oil in a transformer; the presence of methane suggests thatif a fault has occurredit is a lower energy electrical or thermal fault. Much work has been done to correlate predictions from thermodynamic models with actual behavior of transformers. 4.3 Application to equipment All transformers gene

34、rate gases to some extent at normal operating temperatures. But occasionally a gas-generating abnormality does occur within an operating transformer such as a local or general overheating, IEEE Std C57.104-2008 IEEE Guide for the Interpretation of Gases Generated in Oil-Immersed Transformers 5 Copyr

35、ight 2009 IEEE. All rights reserved. dielectric problems, or a combination of these. In electrical equipment, these abnormalities are called “faults.” Thermal, partial discharge, and arcing faults are described in 5.1, 5.2, and 5.3. Internal faults in oil produce the gaseous byproducts hydrogen (H2)

36、, methane (CH4), acetylene (C2H2), ethylene (C2H4), and ethane (C2H6). When cellulose is involved, the faults produce methane (CH4), hydrogen (H2), carbon monoxide (CO), and carbon dioxide (CO2). Each of these types of faults produces certain gases that are generally combustible. The total of all co

37、mbustible gases may indicate the existence of any one, or a combination, of thermal, electrical, or partial discharge faults. Certain combinations of each of the separate gases determined by chromatography are unique for different fault temperatures. Also, the ratios of certain key gases have been f

38、ound to suggest fault types. Interpretation by the individual gases can become difficult when there is more than one fault, or when one type of fault progresses to another type, such as an electrical problem developing from a thermal one. Attempts to assign greater significance to gas than justified

39、 by the natural variability of the generating and measuring events themselves can lead to gross errors in interpretation. However, in spite of this, these gas-generating mechanisms are the only existing basis for the analytical rules and procedures developed in this guide. In fact, it is known that

40、some transformers continue to operate for many years in spite of above-average rates of gas generation. 4.4 Establishing baseline data Establishing a reference point for gas concentration in new or repaired transformers and following this with a routine monitoring program is a key element in the app

41、lication of this guide. Monitoring the health (serviceability) of a transformer must be done on a routine basis and can start anytimeit is not just for new units. Generally, daily or weekly sampling is recommended after startup, followed by monthly or longer intervals. Routine sampling intervals may

42、 vary depending on application and individual system requirements. For example, some utilities sample generator step-up (GSU) transformers four to six times a year, units rated over 138 kV are sampled twice a year, and some 765 kV units are sampled monthly. 4.5 Recognition of a gassing problemEstabl

43、ishing operating priorities Much information has been acquired on diagnosing incipient fault conditions in transformer systems. This information is of a general nature but is often applied to very specific problems or situations. One consistent finding with all schemes for interpreting gas analysis

44、is that the more information available concerning the history of the transformer and test data, the greater the probability for a correct diagnosis of the health of the unit. A number of simple schemes employing principal gases or programs using ratios of key gases have been employed for providing a

45、 tentative diagnosis when previous information is unavailable or indicated no fault condition existed. Principal gas or ratio methods require detectable or minimum levels of gases to be present or norms to be exceeded, before they can provide a useful diagnosis. 5. Interpretation of gas analysis 5.1

46、 Thermal faults Referring to Figure 1, the decomposition of mineral oil from 150 C to 500 C produces relatively large quantities of the low molecular weight gases, such as hydrogen (H2) and methane (CH4), and trace quantities of the higher molecular weight gases ethylene (C2H4) and ethane (C2H6). As

47、 the fault temperature in mineral oil increases to modest temperatures, the hydrogen concentration exceeds that of methane, but now the temperatures are accompanied by significant quantities of higher molecular weight gasesfirst IEEE Std C57.104-2008 IEEE Guide for the Interpretation of Gases Genera

48、ted in Oil-Immersed Transformers 6 Copyright 2009 IEEE. All rights reserved. ethane, and then ethylene. At the upper end of the thermal fault range, increasing quantities of hydrogen and ethylene and traces of acetylene (C2H2) may be produced. In contrast with the thermal decomposition of oil, the t

49、hermal decomposition of cellulose and other solid insulation produces carbon monoxide (CO), carbon dioxide (CO2), and water vapor at temperatures much lower than that for decomposition of oil and at rates exponentially proportional to the temperature. Because the paper begins to degrade at lower temperatures than the oil, its gaseous byproducts are found at normal operating temperatures in the transformer. A GSU transformer, for example, that operates at or near nameplate rating will normally generate several hundred microliters/liter (ppm) of CO and several thousan