1、IEEE Std C57.147-2008IEEE Guide for Acceptance andMaintenance of Natural Ester Fluids inTransformersIEEE3 Park Avenue New York, NY 10016-5997, USA11 July 2008 IEEE Power +1 978 750 8400. Permission to photocopy portions of any individual standard for educational classroom use can also be obtained th
2、rough the Copyright Clearance Center. iv Copyright 2008 IEEE. All rights reserved. Introduction This introduction is not part of IEEE Std C57.147-2008, IEEE Guide for Acceptance and Maintenance of Natural Ester Fluids in Transformers. This guide was prepared by the Insulating Fluids Subcommittee of
3、the Transformers Committee of the IEEE Power Non-Transportation-Related Onshore and Offshore Facilities (Final Rule).6IEEE Std 62, IEEE Guide for Diagnostic Field Testing of Electric Power ApparatusPart 1: Oil Filled Power Transformers, Regulators, and Reactors.7, 8IEEE Std 637-1985 (Reaff 2007), IE
4、EE Guide for the Reclamation of Insulating Oil and Criteria for Its Use. IEEE Std 980, IEEE Guide for Containment and Control of Oil Spills in Substations. IEEE Std C57.104-1991, IEEE Guide for the Interpretation of Gases Generated in Oil-Immersed Transformers.9NFPA 70, National Electrical Code(NEC)
5、.10Official Methods and Recommended Practices of the AOCS, American Oil Chemists Society.116CFR publications are available from the Superintendent of Documents, U.S. Government Printing Office, P.O. Box 37082, Washington, DC 20013-7082, USA (http:/www.access.gpo.gov/). 7IEEE publications are availab
6、le from the Institute of Electrical and Electronics Engineers, 445 Hoes Lane, Piscataway, NJ 08854, USA (http:/standards.ieee.org/). 8The IEEE standards or products referred to in Clause 2 are trademarks owned by the Institute of Electrical and Electronics Engineers, Incorporated. 9IEEE Std C57.104-
7、1991 has been withdrawn; however, copies can be obtained from Global Engineering, 15 Inverness Way East, Englewood, CO 80112-5704, USA, tel. (303) 792-2181 (http:/ 10The NEC is published by the National Fire Protection Association, Batterymarch Park, Quincy, MA 02269, USA (http:/www.nfpa.org/). Copi
8、es are also available from the Institute of Electrical and Electronics Engineers, 445 Hoes Lane, Piscataway, NJ 08854, USA (http:/standards.ieee.org/). 11AOCS publications are available from The American Oil Chemists Society, 2710 S. Boulder, Urbana, IL 61802-6996, USA (http:/www.aocs.org). IEEE Std
9、 C57.147-2008 IEEE Guide for Acceptance and Maintenance of Natural Ester Fluids in Transformers 5 Copyright 2008 IEEE. All rights reserved. 3. Acronyms and abbreviations CFR Code of Federal Regulations cSt centistokes, units of measurement for kinematic viscosity DGA dissolved gas analysis EPA Envir
10、onmental Protection Agency HMWH high molecular weight hydrocarbon MSDS material safety data sheet NEC National Electrical CodePCB polychlorinated biphenyl SIC specific inductive capacity 4. Fluid tests and the significance of each test 4.1 General Many established ASTM tests of practical significanc
11、e can be applied to insulating fluids. The list of tests (see Table 1) and the significance of each test (see 4.3 through 4.18) are offered for classification purposes. (See Clause 2 for ASTM standards referenced in this clause.) Table 1 Insulating fluid tests suitable for natural ester-based dielec
12、tric fluids Significance (subclause) Test ASTM method number 4.2 Practices for sampling D923, D3305 4.3 Neutralization number D664, D974 4.4 Dielectric breakdown voltage D1816 4.5 Dielectric breakdown voltage, impulse conditions D3300 4.6 AC loss characteristicsdissipation factor and relative permit
13、tivity D924 4.7 Interfacial tension D971 4.8 Color D1500 4.9 Kinematic viscosity D445 4.10 Flash point and fire pointCleveland Open Cup Method D92 4.11 Relative density (specific gravity) D1298 4.12 Pour point D97 4.13 Volume resistivity (specific resistance) D1169 4.14 Gas analysis D2945, D3284, D3
14、612 4.15 Oxidation stability TBD 4.16 Water contentKarl Fischer Method aD1533 4.17 Visual examination field test (and color) D1500, D1524 4.18 Gassing of insulating oils under electrical stress and ionization D2300 4.19 Corrosive sulfur test D1275 4.20 Polychlorinated biphenyls (PCBs) D4059 aAlterna
15、te reagents as listed in ASTM D1533. IEEE Std C57.147-2008 IEEE Guide for Acceptance and Maintenance of Natural Ester Fluids in Transformers 6 Copyright 2008 IEEE. All rights reserved. 4.2 Practices for sampling (ASTM D923 and ASTM D3305) ASTM sampling practices are as follows: Practices for samplin
16、g electrical insulating fluids (ASTM D923) Practice for sampling small gas volume in a transformer (ASTM D3305) Accurate sampling, whether of the complete contents or only part thereof, is extremely important from the standpoint of evaluation of the quality of the product sampled. Careless sampling
17、procedures or contamination in the sampling equipment will result in a sample that is not truly representative, leading to erroneous conclusions concerning quality. The appropriate procedures and precautions outlined in ASTM D923 should be followed. 4.3 Acid number (ASTM D664 and ASTM D974) The acid
18、 (neutralization) number for service-aged fluids is, in general, a measure of the acidic constituents of the fluid. It may be useful, if compared to the value for the new product, to detect contamination by substances with which the fluid has been in contact. It may also reveal a tendency toward che
19、mical change or deterioration or to indicate chemical changes in additives. Natural ester fluids have naturally higher acid numbers than hydrocarbon-based fluids, even when new. The acid number may be used as a general guide for determining when oil should be replaced or reclaimed, provided suitable
20、 rejection limits have been established and confirmation is received from other tests. ASTM D664 is the preferred method when testing dielectric fluids that have become discolored, because it uses a potentiometric endpoint rather than a colorimetric endpoint used in ASTM D974. Although the acid numb
21、er indicates relative acid content, the cited methods do not indicate the chemical activity of the acids. Long-chain fatty acids produced by natural ester fluids are less reactive than short-chain organic acids produced by mineral oils. 4.4 Dielectric breakdown voltage (ASTM D1816) The dielectric br
22、eakdown voltage of an insulating fluid is of importance as a measure of its ability to withstand electric stress. It is the voltage at which breakdown occurs between two electrodes under prescribed test conditions. ASTM D1816 prescribes the use of spherically capped electrodes of the VDE type (see V
23、DE 0370-1978 B14).12It serves primarily to indicate the presence of contaminating agents (e.g., water, dirt, conducting particles in the liquid), one or more of which may be present when low dielectric breakdown values are found by test. Care must be taken when filling the test cell with natural est
24、er fluids to guard against trapping air bubbles, which can lead to misleading, low breakdown voltages. Due to their higher viscosity, a longer sample rest time (equal to or greater than 15 min at room temperature) is recommended for natural ester fluids than for mineral oils to allow air bubbles to
25、escape. While the suitability of ASTM D1816 has not been determined for oils having viscosities of more than 19 cSt at 40 C, several manufacturers and users have reported satisfactory results. 12The numbers in brackets correspond to those of the bibliography in Annex A. IEEE Std C57.147-2008 IEEE Gu
26、ide for Acceptance and Maintenance of Natural Ester Fluids in Transformers 7 Copyright 2008 IEEE. All rights reserved. 4.5 Dielectric breakdown voltageImpulse conditions (ASTM D3300) Insulating fluids used in transformers are subjected to transient voltage stresses while being subjected to steady-st
27、ate voltage stresses associated with continuous operation of the apparatus at commercial power frequencies. The ability of the insulating fluid to withstand transient voltage stresses has become important to the designers of transformers. Transient voltages may be either negative or positive in pola
28、rity. Although polarity of the voltage wave has little or no effect on the breakdown strength of an oil in uniform fields, polarity does have a marked effect on the breakdown voltage of an oil in nonuniform electric fields. Transient voltages may also vary over a wide range in both the time to reach
29、 crest value and the time to decay to half-crest or to zero magnitude. The standard impulse test, ASTM D3300, specifies a 1.2 s 50 s negative polarity wave. The standard wave shape for switching surge tests on transformers is 100 s to crest and greater than 1000 s to zero. The purchaser of an impuls
30、e generator may want to specify the necessary features to make switching surge tests possible. Consideration may be given to other electrode configurations such as VDE electrodes, which are similar to those used in ASTM D1816, since it may be desirable to obtain the ratio between power frequency and
31、 impulse breakdown under similar conditions. Care must be taken when filling the test cell with natural ester fluids to guard against trapping air bubbles, which may result in misleading, low breakdown voltages. Due to their higher viscosity, a longer sample rest time (equal to or greater than 15 mi
32、n at room temperature) is recommended prior to impulse testing natural ester fluids than for mineral oils to allow air bubbles to escape. 4.6 AC loss characteristicsDissipation factor and relative permittivity (ASTM D924) This method describes the determination of dissipation factor and relative per
33、mittivity of new electrical insulating fluids as well as liquids in service or subsequent to service in transformers. Dissipation factor (power factor) is a measure of the dielectric losses in an electrical insulating fluid in an alternating electric field and of the energy dissipated as heat. A low
34、 dissipation factor indicates low dielectric losses. Losses due to dissipation factor should not be confused with transformer load and excitation losses, which are indicative of the transformers energy efficiency. The losses associated with dissipation factor are several orders of magnitude lower th
35、an the load and excitation losses. New natural ester fluids have inherently higher dissipation factors than mineral oils. Field data indicates a higher rate of increase in the dissipation factors under normal operating conditions relative to mineral oils. Before acceptance limits for service-aged na
36、tural esters can be established, additional field data must be collected and analyzed. Relative permittivity, often referred to as dielectric constant and occasionally as specific inductive capacity (SIC), is the ratio of the capacitance of a capacitor using the material to be measured as the dielec
37、tric to the capacitance of a capacitor with vacuum as the dielectric, both having identical electrodes. The relative permittivities of materials in contact with each other affect the local voltage stress distribution. New natural esters have inherently higher relative permittivity than mineral oils,
38、 closer to that of cellulose insulation leading to an improvement in electrical stress distribution. IEEE Std C57.147-2008 IEEE Guide for Acceptance and Maintenance of Natural Ester Fluids in Transformers 8 Copyright 2008 IEEE. All rights reserved. 4.7 Interfacial tension (ASTM D971) This method cov
39、ers the measurement, under nonequilibrium conditions, of the interfacial tension of insulating fluids against water. The interfacial tension between electrical insulating fluids and water is a measure of the molecular attractive force between their unlike molecules at the interface. It is expressed
40、as millinewtons per meter (mN/m). This test has been used as one means of detecting soluble polar contaminants and products of deterioration in mineral oil. Soluble-contamination or fluid-deterioration products generally decrease the interfacial tension value. However, ASTM has not published an acce
41、ptance value limit for interfacial tenstion of new natural ester fluids. Natural ester fluids have inherently lower interfacial tension than new mineral oils, typically between 25 mN/m to 30 mN/m (ASTM D6871-2003, Appendix X 2.1.2). This difference is due to an inherent difference of ester and miner
42、al oil chemistry, including higher absorption levels for water. Until ASTM has published a limit for interfacial tension of new natural ester fluids, this guide will not include such a limit value. Additional field data will also be required before limits for field-aged fluid can be established for
43、this guide. However, a greater than 40% decrease from the initial values in fluid as received in a new transformer from an operating unit should trigger further investigation. 4.8 Color (ASTM D1500) A low color number of a mineral insulating oil is desirable to permit inspection of assembled apparat
44、us in a tank. An increase in color number during service is an indicator of oil deterioration or contamination. New natural ester fluids may initially be slightly darker in color, typically a slight amber appearance, than highly refined new mineral oil. Other tests (such as dissipation factor and ne
45、utralization number) are better measures of fluid deterioration or contamination. Note that natural ester fluid manufacturers may add clear colorants for identification purposes. Such tints should not impact the ASTM color and visual examinations. 4.9 Kinematic viscosity (ASTM D445) The viscosity of
46、 dielectric coolants within the range of normal operating temperatures is important because it can impact both the cooling and performance of some internal components, such as internal load tap changers. Viscosity is the measure of the resistance of a fluid to flow. Kinematic viscosity is the ratio
47、of the viscosity of a fluid to its density. The viscosity of insulating oil and natural ester fluids is usually measured by the time of flow of a given quantity of oil under controlled conditions. The viscosity at the operating temperatures of electrical insulating fluids influences their heat trans
48、fer properties in natural and forced (pumped) convective flow and, consequently, the temperature rise of operating transformers containing them. Natural esters typically have higher viscosity than mineral oils. An increase in viscosity over time may indicate excessive oligomerization of natural este
49、rs, typically due to abnormal exposure to air and heat. 4.10 Flash point and fire pointCleveland Open Cup Method (ASTM D92) The flash point of a flammable liquid is the lowest temperature at which the vapor pressure is sufficient to form a flammable mixture with air near the surface of the liquid. The fire point is the lowest temperature at which a liquid in an open container will attain a vapor pressure sufficient to continue to burn when once ignited. Low values of either flash or fire point may be used to provide a qualitative
