1、IEEE Std C57.140-2006IEEE Guide for the Evaluation and Reconditioning of Liquid Immersed Power TransformersI E E E3 Park Avenue New York, NY 10016-5997, USA27 April 2007IEEE Power Engineering SocietySponsored by theTransformers Committee IEEE Std C57.140-2006 IEEE Guide for the Evaluation and Recond
2、itioning of Liquid Immersed Power Transformers Sponsor Transformers Committee of the IEEE Power Engineering Society Approved 16 November 2006 IEEE-SA Standards Board Abstract: This guide includes guidelines for the following: insulating oil maintenance and diagnostics, oil reclamation, testing metho
3、ds for the determination of remaining insulation (paper) life, and upgrades of auxiliary equipment such as bushings, gauges, deenergized tap changers (DETCs), load tap changers (LTCs) (where applicable), and coil reclamping. The goal of this guide is to assist the user in extending the useful life o
4、f a transformer. Keywords: evaluation, life extension, reconditioning, risk assessment _ The Institute of Electrical and Electronics Engineers, Inc. 3 Park Avenue, New York, NY 10016-5997, USA Copyright 2007 by the Institute of Electrical and Electronics Engineers, Inc. All rights reserved. Publishe
5、d 27 April 2007. Printed in the United States of America. IEEE is a registered trademark in the U.S. Patent +1 978 750 8400. Permission to photocopy portions of any individual standard for educational classroom use can also be obtained through the Copyright Clearance Center. Introduction This introd
6、uction is not part of IEEE Std C57.140-2006, IEEE Guide for the Evaluation and Reconditioning of Liquid Immersed Power Transformers. At the turn of the century, approximately one half of all transformers used in the electric utility industry reached their 30 yr design life. Because of todays economi
7、cs, many of these transformers will be called upon to supply reliable service for an additional 20 yr to 30 yr. Any transformer owner intending to significantly extend the life should address three key areas: economics, inspection and diagnostics, and materials and design. A comprehensive economic s
8、tudy should be carried out before the investment of significant resources. This study involves load forecasts, reserve margins, new capacity plans, cost-benefit analyses, operating costs, capital costs, and continued reliability and availability. Once a financial decision to extend the transformer l
9、ife is made, an inspection and diagnostic strategy should be determined. This evaluation should include the following: manufacturer, size, age, operating history, thermal load, electrical tests, maintenance history, and failure history. New materials, major component replacement, and other design ch
10、anges may also affect the life extension decision. The development of better core steel and better solid insulation has been ongoing for a number of years. The better operating efficiency of new materials may make life extension uneconomical. Notice to users Errata Errata, if any, for this and all o
11、ther standards can be accessed at the following URL: http:/ standards.ieee.org/reading/ieee/updates/errata/index.html. Users are encouraged to check this URL for errata periodically. Interpretations Current interpretations can be accessed at the following URL: http:/standards.ieee.org/reading/ieee/i
12、nterp/ index.html. Patents Attention is called to the possibility that implementation of this guide may require use of subject matter covered by patent rights. By publication of this guide, no position is taken with respect to the existence or validity of any patent rights in connection therewith. T
13、he IEEE shall not be responsible for identifying patents or patent applications for which a license may be required to implement an IEEE standard or for conducting inquiries into the legal validity or scope of those patents that are brought to its attention. iv Copyright 2007 IEEE All rights reserve
14、d Participants This guide was prepared by the Guide for the Evaluation and Reconditioning of Liquid Immersed Power Transformers Working Group, with guidance from the Power Transformer Subcommittee. At the time this guide was completed, the working group had the following membership: Rowland James, C
15、hair William Bartley, Co-Chair however, copies can be obtained from Global Engineering, 15 Inverness Way East, Englewood, CO 80112-5704, USA (http:/ 7Numbers in brackets correspond to the numbers in the bibliography in Annex A. 2 Copyright 2007 IEEE All rights reserved IEEE Std C57.140-2006 IEEE Gui
16、de for the Evaluation and Reconditioning of Liquid Immersed Power Transformers 3.1.2 furanic compound: A family of molecules created by the thermal degradation of cellulose. Furanic compounds are derived from a heterocyclic five-member hydrocarbon that includes oxygen and two double bonds. 3.1.3 gas
17、 chromatography: A process in which the material sample is vaporized and injected into a stream of carrier gas (as nitrogen or helium) moving through a column containing a stationary phase composed of a liquid or particulate solid. The material is then separated into its component compounds accordin
18、g to their affinity for the stationary phase. 3.1.4 static electrification (oil-immersed transformers): A surface charge imbalance caused by solid insulation in contact with flowing oil. This imbalance results in a charge accumulation in oil that increases potential-producing electrical discharge. 3
19、.2. Acronyms and abbreviations BIL basic impulse level DETC deenergized tap changer DGA dissolved gas analysis DP degree of polymerization FAL furfural FRA frequency response analysis LTC load tap changer LTI liquid temperature indicator MSD molecular sponge dryout PCB polychlorinated biphenyl PD pa
20、rtial discharge RIV radio influence voltage RPRR rapid pressure rise relay WTI winding temperature indicator 4. Risk assessment For the purpose of this guide, the term failure is defined as any unscheduled event on or in the transformer that requires the transformer to be removed from service for co
21、rrective action. A failure of an ancillary component might cause a relay to trip the transformer for reasons not relating to the transformer itself, and such a trip does not constitute a transformer failure according to the intentions of this guide. Because the decision to remove a transformer from
22、service will vary with different users, users should create their own specific models based on the general models in this clause. The term fault as used in this clause is not restricted to the traditional electric utility usage, i.e., an unintentional phase-to-ground or phase-to-phase dielectric fai
23、lure. Instead, in this clause, the term fault may refer to a broader definition, such as a malfunction, defect, or indication of deterioration of a component. Evaluating and reconditioning of large liquid-filled transformers are obviously not trivial exercises. Dual objectives of meeting the growing
24、 demand of the electric power grid and maintaining system reliability may require significant changes in the way an owner operates and cares for its transformers. An emerging industry strategy is a life-cycle management program that sets loading priorities and provides strategic direction for all of
25、 an owners transformer assets. For the owner that has many transformers, it is usually not economically feasible to subject every aging transformer to a rigorous inspection and extensive testing. Thus, this asset management approach is typically a three-step process: a) Priority screening of transfo
26、rmer fleet b) Diagnostic testing c) Condition assessment of individual transformers 3 Copyright 2007 IEEE All rights reserved IEEE Std C57.140-2006 IEEE Guide for the Evaluation and Reconditioning of Liquid Immersed Power Transformers In order to identify and prioritize a long list of aging transfor
27、mers, a screening process is often used. The screening could be as simple as ranking the transformers by age. However, a more comprehensive screening can be accomplished with a risk assessment method. There are many different risk assessment methods and strategies available to the utility industry f
28、or a large family of power transformers. The method discussed here is a simple procedure called fault tree analysis, which can help identify the transformers that need additional condition assessment, additional testing, and/or other actions for the purpose of bringing the entire population up to an
29、 acceptable risk level. Each transformer in a group can have its risk index compared, or ranked, to all other transformers on the companys balance sheet. The risk-based screening process uses statistical methods to identify and prioritize the transformers that represent the highest risk for the owne
30、r. But this step does not identify the actual condition or the vulnerability of the individual transformers. Once the screening process has established a priority list, the next two steps in the process, diagnostic testing (see Clause 5) and condition assessment and evaluation (see Clause 6), can he
31、lp the owner establish a detailed asset management strategy. However, the list of variables and the individual utility circumstances that govern the technical and financial decision making are such that it is impossible to establish an industry-wide set of rules or standards for managing the life cy
32、cle of aging transformers. The cost of a failure can vary greatly. Any analysis of potential costs of a failure should consider the possible repair or replacement costs of the transformer or failed component, environmental impact and clean-up costs, damage to adjacent equipment, lost revenues and li
33、tigation costs, as well as any other site-specific potential costs. There is also a large variability in the possible scope of the failure. A component failure may simply cause a momentary outage and require only a component replacement, or it could lead to a catastrophic failure with an insulating
34、fluid spill and/or a large fire. The relative probability of each type of failure needs to be considered in the calculation of risk. The next eleven subclauses (4.1 through 4.11) describe key issues that affect the risk of failure. In the most general sense, risk is defined as futures uncertainty an
35、d has two basic components: the frequency or probability of undesirable events (i.e., how often undesirable events occur) and the severity or consequences of those events (i.e., how much the failure will cost). Obviously, many of these issues address the probability of failure, but some of them affe
36、ct the severity of the failure. Risk-based methods generally use the product of both the frequency and severity of events together in the analysis process. Regardless of whether the frequency and severity data are subjective, qualitative, or quantitative, a risk-based decision process provides a log
37、ical framework to capture and portray several layers of complex data in one cohesive, easily interpreted format. 4.1. Impact on the system To conduct a risk assessment of all the transformers in a users system, one of the severity factors that should be addressed is the particular transformers curre
38、nt and future value in its service position. System operating requirements may have changed since each particular transformer was originally installed. Consideration should be given to the functionality of each individual transformer with respect to the strategic impact of the system. Some questions
39、 that should be addressed include the following: Will the transformer meet future load projections? Is there any change in impedance needed to limit fault duty or improve regulation? Does transformer design quality impact system reliability? Although somewhat subjective, answers to such questions wi
40、ll help to define the consequences for a particular transformer failure. System reliability will influence the decision of whether to invest in extending transformer useful life. Transformer rating may necessitate up-rating, if feasible, to meet anticipated transformer-loading 4 Copyright 2007 IEEE
41、All rights reserved IEEE Std C57.140-2006 IEEE Guide for the Evaluation and Reconditioning of Liquid Immersed Power Transformers requirements. A change in impedance may be required of a redesigned transformer to limit fault duty or improve reactive power performance and/or improve voltage regulation
42、 to acceptable levels. Economic considerations may include cost of transformer losses, maintenance, and undelivered energy when the loss of the transformer results in a loss of ability to supply load on the system and costs associated with failure including customer incentives. 4.2. Vintage Manufact
43、urer and vintage can be a factor of transformer quality, material, and component condition. Transformers manufactured in the United States before 1967 were likely designed without the use of computers. Being conservatively rated, these transformers may have higher loading capability. However, they m
44、ay lack adequate provision for leakage flux, have a higher probability of localized hot spots, and have high core losses (due to the quality of core steel available at the time of manufacture). The use of improved quality core steel has reduced the core losses significantly in many of the transforme
45、rs built since the mid-1980s. Modern core cutting and stacking techniques have also resulted in reducing core losses. Thermally upgraded paper was first introduced in the 1950s, but not widely used by transformer manufacturers until the 1960s. Care must be taken to evaluate temperature-related chara
46、cteristics of older transformers that do not contain thermally upgraded cellulose insulation (based on a rated temperature rise of 55 C) as compared to those with the upgraded insulation (a rated temperature rise of 65 C). Such aspects of original product quality should be assessed. Insulation defec
47、ts may result from improper assembly, inherent material defects (such as a burr on the conductor), a rough edge on a brazed connection, or damage to the conductor insulation. Defects could be intensified by coil vibration caused during shipment and normal operation. This situation can be monitored b
48、y conducting a frequency response analysis (FRA) test and leakage reactance test. Results of these two tests may be kept as a record and compared with future results when these two tests are performed again periodically. In evaluating the suitability for intended service, the original intended duty
49、and specification should be compared to the anticipated loading and system condition (e.g., fault duty, regulation, stability) as these requirements could exceed the original intended capabilities of the transformer. Caution needs to be taken that an existing unit auxiliary transformer or station transformer may not be used as a generator transformer unless there is ample verification of its withstand capability to the new load pattern. 4.3. Vacuum withstand capability Filling a non-vacuum-rated transformer from the bottom w
