Electrical and chemical diagnostics of transformers insulation. B.Accelerated aged insulation samples

This paper describes the analysis of accelerated aged insulation samples to investigate the degradation processes observed in the insulation from aged power transformers. Short-term accelerated ageing experiments were performed on paper-wrapped insulated conductors and on pressboard samples. The condition of aged insulation samples was investigated by two relatively new diagnostic techniques: (a) measurements of interfacial polarization spectra by a DC method; and (b) measurements of molecular weight and its distribution by gel permeation chromatography (GPC). Several other electrical properties of the paper/pressboard samples were also studied. Possible correlations have been investigated among the different measured properties. The GPC results have been used to predict how power transformer insulation molecular weights change with temperature and time     

Investigating the effects of oxidation and thermal degradation onelectrical and chemical properties of power transformers insulation

This paper describes the analysis of thermally accelerated aged insulation samples to investigate the degradation processes observed in the insulation of aged transformers. Accelerated ageing experiments were performed on paper wrapped insulated conductors in the presence of air and nitrogen environments over a temperature range of 115 to 145°C. Effects of oxidation on the ageing of oil-paper insulation were investigated and results are presented in this paper. The condition of aged insulation samples was investigated by a number of diagnostic techniques: (a) measurements of interfacial polarization spectra by the return voltage method, (b) measurements of molecular weight and its distribution by gel permeation chromatography, (c) surface analysis by X-ray photo-electron spectroscopy, and (d) a study of the oxidation of the oil by UV-visible spectroscopy. Results from these measurements are presented in this paper and are used to analyse the degradation process with special emphasis on oxidation     

宝钢高能耗配电变压器的淘汰更新

尽管配电变压器的能源转化效率较高，但因其在供配电网络中数目众多，具有较大的节能空间。分析了高能耗配电变压器淘汰更新问题及宝钢配电变压器现状，针对宝钢高耗能配电变压器淘汰更新的具体技术进行了讨论，对类似企业的高能耗变压器淘汰更新工作提供参考。     

The transformer short-circuit test and the high power laboratory in China the past, present, and future

Over the last half-century, the transformer industry in China has experienced substantial development due to the study of the short-circuit performance of power transformers by using short-circuit tests. This is because power transformers operating in power systems are exposed to short circuits, which cause high short-circuit currents of more than 10 times the rated current and are dangerous to the transformer. In this paper, the author reviews short-circuit testing of distribution transformer, including power transformers. The Hushita I High Power Test Laboratory is also described in this paper along with its main equipment and test capabilities. Potential for future development is also discussed.     

电力电子变压器电路拓扑与控制策略研究

介绍了与传统电力变压器的概念有着极大不同的电力电子变压器。着重分析了电力电子变压器的工作原理及其主要拓扑结构、典型控制策略，并对拓扑和控制策略提出了多项改进措施。在此基础上，探讨了实现电力电子变压器的关键技术，并提出了有效的解决方案。最后根据交流柔性输电技术发展的需求，提出了电力电子变压器的多项扩展功能。     

S11型配电变压器的技术经济分析及应用

阐述我国S11型配电变压器的发展过程，分析比较了卷铁芯和叠铁芯2种结构的优缺点，并对S11和S9型配电变压器的损耗参数进行比较。建立了S11型配电变压器技术经济分析的数学模型，对更换S9型和S7型配电变压器的投资回报以及使用S11型配电变压器对广电集团公司电网线损的贡献分别进行了分析和测算。计算表明S11型配电变压器具有非常可观的经济效益。S11型配电变压器的技术已趋成熟，生产已具规模，具备大批量采购的条件，建议新采购时应以S11型配电变压器为主，对于运行12a及以上的老旧S7型（或更早期的）配电变压器应考虑逐步更换。     

Measuring and understanding the ageing of kraft insulating paper inpower transformers

In this paper we discuss the application of a number of techniques that are currently being developed for use in life assessment/condition monitoring of transformer insulation, and we illustrate possible applications with some recent data. These include: high performance liquid chromatography (HPLC) of the oil to measure the product concentrations; size exclusion chromatography (SEC) of the paper to measure changes in molecular weight distribution (related to the degree of polymerization, DP) and computer modeling of the degradation process to relate chemical degradation rates to changes in physical properties, such as tensile strength, which is of critical importance in assessing the probability of damage to the paper under fault conditions. We also revisit the use of DP measurement as a means of assessing insulation life and present results that illustrate problems that we have identified in obtaining consistent data. We describe a method, developed from the British and American standards, which enables us to obtain reproducible results with a known variance. The aims of this paper are to present a limited review of techniques that are relatively new to the transformer monitoring field, to provide some recent results from this laboratory to demonstrate their potential application, and to show the need for a range of new tools, if we are to improve our ability to assess the condition of transformers and the remanent life of their insulation     

电压响应方法在电力变压器状态评估中的应用(英文)

Power transformer is one of the most important equipment in the power system.Its operating condition affects the reliability of power supply directly.Therefore,in order to guarantee transformer operation safely and reliably,it is necessary to assess condition of power transformer accurately.Return voltage method based on voltage response measurements is still a new non-intrusive diagnosis method for internal insulation aging of transformer.In this paper the technique and application of return voltage measurement and some results of voltage response measurements of several transformers was introduced.Voltage response measurements were performed on various transformers with different voltage grades,various operating periods,different moisture contents and aging degrees on site.Derived moisture contents from return voltage measurement were compared with the corresponding moisture contents obtained from the analysis of oil samples.Based on on-site experiments and theoretical analysis,the criteria for insulation state of transformer are proposed.Moisture condition of transformer insulation can be determined by using return dominant time constant,and a good correlation between aging degree and the return voltage initial slopes of the aged transformers.Field test performed on several transformers,its interpretation of results are also presented,which proves that return voltage measurements can be used as a reliable tool for evaluating moisture content in transformer insulation.     

高温超导变压器

高温超导变压器与常规变压器相比 ,具有体积小、重量轻、效率高、无火灾隐患、不污染环境和限制短路电流改善系统动态稳定性等诸多优点。阐述了欧洲、美国及日本等国家的高温超导变压器的研究现状、基本特点、优越性及研究中存在的技术问题等。并且讨论了高温超导变压器的设计原则和将来其投入电力系统运行时所需要进一步考虑的问题     

Effects of open-wye/open-delta transformers on the operation of distribution systems

Transformers with open-wye/open-delta connections have been widely used in electrical distribution systems, the advantage being that both three-phase and single-phase loads may be supplied by using only two single-phase transformers. In this paper, the equivalent circuit of the transformer bank was derived for the computer simulation of a distribution system. The models were verified with laboratory experiments. A sample feeder with this type of transformer was used to demonstrate its effect on the operation of a distribution system. The power flow and voltage imbalance which were induced by this transformer were analyzed. The relationship between the system imbalance and the power factor of a three-phase load was also investigated.     

厂用电变压器满负荷并环运行讨论

针对厂用电变压器在并列操作过程中容易造成过负荷的情况,讨论了变压器在并列时由于各变比的差异而引起的循环功率,造成变压器负荷分配不合理的问题,介绍了使变压器在较佳的状态下运行,在不同运行工况所采用的调整手段,以及变压器在并列操作中应注意的问题。     

Thermal Analysis of Power Transformer Using an Improved Dynamic Thermal Equivalent Circuit Model

Abstract

—To insure the health of power transformers insulation, its heat distribution in different operating conditions must be determined. In extended thermal equivalent circuits (TECs), less attention has been paid to losses and temperature distribution of different parts such as core, tank and metallic regions of transformer. Most previous works, hot-spot temperature of winding and top-oil were considered by available no-load and on-load losses of transformer. This paper extends the TEC to be able to evaluate fully the different operating conditions of transformer. Estimation of losses of different elements of transformer as heat generating source and thermal parameters of transformer are introduced as two major challenges of the proposed model. At this end, an appropriate three-dimensional finite element method is used to estimate the losses of different components of power transformer. In addition, to identify the transformer thermal parameters, a genetic algorithm is used by searching in chosen measurements. Finally, the results obtained by the TEC are compared with IEEE-Annex G method and measured temperature and high accuracy of the proposed model in temperature estimation in different parts of transformer are shown.     

有载调容变压器在农村电网中的应用

变压器损耗在电网损耗中占有较大的比重,因此降低配电变压器损耗成为有效的节能措施之一。介绍了有载调容变压器的结构与节能原理以及采用有载调容变压器后带来的经济效益,预期了有载调容变压器在农村电网中的应用前景。     

The determination of FFA concentration in transformer oil byfluorescence measurements

Condition monitoring of the paper winding of power transformers involves the measurement of the concentration of 2-furaldehyde, also called furfuraldehyde (FFA) in the transformer oil. Measuring the concentration of FFA in the oil gives a reliable indication of the condition of the paper insulation. This measurement has routinely been performed by using techniques such as high performance liquid chromatography. We report for the first time the use of fluorescence-based methods for the assessment of FFA in transformer oil     

B1 field-insensitive transformers for RF-safe transmission lines

Objective: Integration of transformers into transmission lines suppresses radiofrequency (RF)-induced heating. New figure-of-eight-shaped transformer coils are compared to conventional loop transformer coils to assess their signal transmission properties and safety profile. Materials and methods: The transmission properties of figure-of-eight-shaped transformers were measured and compared to transformers with loop coils. Experiments to quantify the effect of decoupling from the B₁ field of the MR system were conducted. Temperature measurements were performed to demonstrate the effective reduction of RF-induced heating. The transformers were investigated during active tracking experiments. Results: Coupling to the B₁ field was reduced by 18 dB over conventional loop-shaped transformer coils. MR images showed a significantly reduced artifact for the figure-of-eight- shaped coils generated by local flip-angle amplification. Comparable transmission properties were seen for both transformer types. Temperature measurements showed a maximal temperature increase of 30K/3.5 K for an unsegmented/ segmented cable. With a segmented transmission line a robotic assistance system could be successfully localized using active tracking. Conclusion: The figure-of-eight-shaped transformer design reduces both RF field coupling with the MR system and artifact sizes. Anatomical structure close to the figure-of-eight-shaped transformer may be less obscured as with loop-shaped transformers if these transformers are integrated into e.g. intravascular catheters.     

Analysis of Temperature Distribution in Cast-resin Dry-type Transformers

Non-flammable characteristic of dry-type cast- resin transformers make them suitable for residential and hospital usages. However, because of resin’s property, thermal behavior of these transformers is undesirable, so it is important to analyze their thermal behavior. Temperature distribution of cast-resin transformers is mathematically modeled in this paper. The solution of the model was carried out successfully by finite difference method. In order to validate the model, the simulation results were compared with the experimental data measured from an 800 kVA transformer. Finally, the influences of some construction parameters and environmental conditions on temperature distribution of cast-resin transformers were discussed.     

油纸绝缘变压器老化特征分析

目前,国内外学者对回复电压法做了大量的研究,但是还没有一个明确评估变压器油纸绝缘老化状态的方法。在理解介质极化特性的前提下,以变压器油纸绝缘极化等效电路模型为基础,仿真分析了回复电压特征量随极化等效电路参数(极化电阻、极化电容以及支路数)变化的规律。仿真结果表明,回复电压峰值的最大值、回复电压初始斜率最大值及主时间常数等可用来评估变压器绝缘状况。同时,等效电路模型的支路数也可辅助评估变压器的绝缘状况。最后对多台实际变压器进行测试分析,验证了上述特征量用于评估变压器绝缘状态是可行的。     

基于分布反馈半导体激光器的CO气体光声光谱检测特性

一氧化碳(CO)是变压器油中溶解的主要故障特征气体之一,能有效反映运行电力变压器中油纸绝缘的放电及老化;而光声光谱(photoacoustic spectroscopy,PAS)技术能够应用于变压器油中溶解气体的在线监测。基于光声光谱检测原理,利用分布反馈(distributed feedback,DFB)半导体激光器搭建了CO气体光声光谱检测平台,选择1.567m的CO分子谱线为研究对象,实验研究了DFB半导体激光器的辐射特性和CO气体的光声光谱响应特性,分析了光声信号与激光功率、气体浓度的关系。结果表明:在气体吸收未发生饱和效应的条件下,光声信号与激光功率、气体浓度均具有良好的线性关系。该研究结果为变压器油中气体光声光谱的在线监测奠定了基础。     

Transformer tank vibration modeling as a method of detecting winding deformations-part II: experimental verification

In Part I of the paper, a tank vibration model was proposed as a method to detect the winding deformations in power transformers. This model is incorporated in a model-based monitoring system for power transformers. In this paper, the experimental verification of the proposed model that calculates vibration on the transformer tank is reported. The model was validated in a 1500-kVA experimental transformer constructed as a reduced scale model of a 60-MVA 220-kV unit. In order to load the test transformer, the opposition method described in IEC 60076-2 Standard was used allowing to vary the load and power factor over a wide range. Sensors to measure vibrations and temperature were installed in the test transformer. The model was validated under different test transformer operating conditions. In order to verify the model's ability to detect failures, a deformation was provoked in the test transformer winding. Model predictions were compared with the measured vibration in that situation. The model has also been applied to four (30-40 MVA) grid transformers. Some results of this field validation are presented in this paper.