Analysis of water in oil-impregnated kraft paper and its effect onconductivity

Oil impregnated paper or polymer film is the main insulating system for many kinds of power apparatus. The oil impregnated materials, especially oil impregnated kraft paper, include a significant amount of water, and this water disturbs the insulating performance of the devices. The amount of water in the materials usually is represented by the difference in weight between the normal material and the same material after drying. However it is difficult to measure the absolute value of the water content and to determine the state in which the water exists in the materials. In this study, we examined the IR spectra of water in oil impregnated kraft paper, because the IR spectrum of the water indicates not only the amount of water but also its state. It was found that most of the water behaves as liquid water, and some as hydrogen bonded water, interacting with the paper fiber. The dc conductivity of the kraft paper depends only on the amount and state of the water associated with it whether or not the paper is impregnated with the oil     

Virtual valuations [transformer testing]

Modern power transformers are tightly designed to minimise volume, weight and cost. One solution to striking this delicate balance is to test the transformer in a virtual way at the design stage, through numerical simulation. When power transformers fail to meet their specification, it is almost always due to a very localised effect. such as a hot spot on the tank wall or an insulation breakdown at a critical point in the winding. Finite element methods are ideally suited to calculating local electric and magnetic field variations and, for more than 30 years, have been used for examining the performance of power transformers.     

The transformer [historical overview]

Just a century ago, the transformer made the distribution of electric power a practical endeavor. Many elements of modern life depend on it, yet it remains one of technology's unsung heroes. This article presents an historical overview of the development and application of the transformer     

变压器总烃超标原因分析与处理

利用油中溶解气体分析,预测运行中的充油变压器是否处于良好状态已是对变压器技术监测的必备手段。通过对内蒙古国华准格尔电厂2号主变压器油色谱中总烃超标分析,应用三比值法初步判断变压器内有726℃的高温过热故障。结合2008年变压器春检试验中发现低压侧直流电阻不平衡率超标现象,通过专家分析,决定对国华准电2号主变压器进行吊罩检查大修。通过前期周密的筹备和检修过程中的科学管控,成功查出并处理了2号主变压器低压侧一引线断裂导致过热隐患。该项目对电力同行变压器故障判断有指导意义。     

Spectroscopic measurement and analysis of water and oil in transformer insulating paper

A portable fiber-optic spectroscopic system (TRANSPEC) has been developed for nondestructive measurement of aged transformer insulating paper. Following successful measurement of degree of polymerization (DP) of a range of transformer-aged paper samples, the system has now been shown to separate the oil and paper information for measurement of DP in oil-wetted paper samples. In addition, the system has been shown to be capable of the prediction of both oil and water content of paper to a high accuracy, and is also capable of identifying and quantifying different water species. Spectroscopic measurements have been used together with gravimetric water adsorption measurements to investigate the kinetics of uptake of water vapour into paper from air in the case of nominally dry and oil-impregnated samples. Relationships between water adsorption parameters and properties of the paper insulation have also been investigated using measurements under controlled conditions.     

变压器油中氢气含量情况分析及解决方法

阐述变压器油中氢气含量增高形成机理。对牡丹江电厂5号低压厂用变压器油中氢气含量异常的原因进行了分析,提出了防止变压器油中氢气含量增高的技术措施。     

Breakdown of transformer oil

Some of the factors affecting the dielectric strength of transformer oil are investigated. These factors include the stabilization phenomenon, oil and electrode pretreatment, the effect of oil velocity, the effect of a capacitance parallel to the test cell, and the effects of electrode area and gap spacing. The experimental apparatus and procedure are described, and the results are presented for each of the above factors. Suggestions for future research are offered     

Measurement of the space charge field in transformer oil using itsKerr effect

Nonuniform electric fields >80 kV/cm, have been measured via a relative optical intensity measurement by exploiting the Kerr effect in transformer oil. Transformer oil was used as a Kerr medium in these measurements. Neither a knowledge of the Kerr coefficient nor the actual value of maximum transmitted intensity are required to obtain the absolute value of the electric fields. Electric fields were measured with ac and dc excitations. Space charges resulting from charge injection have been found in transformer oil at room temperature under electric stresses >150 kV/cm with ac excitation and 90 kV/cm under dc excitation. The magnitudes of space charges in transformer oil with ac applied voltages varied from 2 to 50 nC/cm³. The magnitudes of space charges with dc excitation varied from 60 pC/cm³ to 10 nC/cm³. The results illustrate the limitations of the electro-optic technique for investigations of the interfacial electric fields (gas-solid) with transformer oil as the Kerr medium     

Technical report-particles in transformer oil

Attention is drawn to a parameter that plays a crucial role in determining the breakdown strength of transformer oil, yet which tends to be ignored. This parameter is the settling time, which can mean either the time interval between two consecutive measurements or the time for which an oil sample is stored before measurements begin. The term is used here in the former sense. Research carried out with Bruce profile electrodes and for gap spacings of 1 and 4 mm showed that settling times between measurements of 1 and 5 mm gave widely differing breakdown strength results. The breakdown strength with 1-min settling time was inferior to that for a settling time of 5 min. A particle counting analysis performed on two oil samples supports the hypothesis that short settling times do not allow either the bubbles from the previous breakdown to be dissolved or the decomposition products to settle under the influence of gravity, thereby increasing the probability of breakdown     

A newly modified forced oil cooling system and its impact on in-service transformer oil characteristics

This paper introduces a newly modified forced oil-cooling system, which comprises a bypass filter (BPF). The BPF has been introduced in such a way that its intake oil is the hot oil from the transformer top and to deliver it at the inlet of the oil-circulating pump. This system has been used for two transformers. Periodical measurements of the physical, chemical, and electrical transformer oil characteristics by standard testing methods before BPF operation, in operation and after stopping its operation in the transformer have been carried out. Before BPF operation, the results revealed that these characteristics are continuously deteriorating with the increase in transformer oil service period. However, when BPF is in operation, this deterioration not only has been reduced but also some of the characteristics have been improved. After the operation of BPF has been stopped, some of the characteristics resumed their deterioration. However, the rates by which these characteristics are deteriorating are noticeably smaller than their initial values. The deteriorated transformer oil characteristics (without installation of BPF) have been predicted by polynomial regression, multiple linear regression, and general linear multiple regression models. The efficiency and feasibility of the new cooling system in preserving in-service transformer oil characteristics have been proved and justified by quantitative evaluation of the measured and theoretically predicted deteriorated (without installation of BPF) characteristics.     

Water saturation limit of transformer oils - [feature article]

The stable functioning of power transformers is closely related to the state of their insulation systems [1]. Most power transformers at present employ paper/oil insulation [2]. This type of insulation has many advantages, but deteriorates under the combined influence of a number of interrelated factors. The insulation properties of the paper/oil system depend strongly on the degree of aging, moisture accumulation in the oil and the paper, and the migration of moisture between them.     

Properties of streamers in transformer oil

The electrical characteristics of creeping discharges and single creeping streamers in transformer oil first are compared with those of streamers developing in the liquid bulk. The distribution of electric potential along the channel of a single negative creeping streamer is determined using a capacitive probe technique. Then the distribution of the space charge associated with each streamer channel is discussed and the electric field around the channels is estimated. A strong correlation between the mean potential gradient and the capacitance of the streamer channels is found. The different results and considerations tend to support the hypothesis of the same basic physical mechanism for both creeping discharges and streamers developing in the bulk     

大型变压器绝缘油中硫腐蚀的危害及防护对策研究

针对电网大型变压器在运行中发现的硫腐蚀问题,初步分析了产生硫腐蚀的原因及对设备安全运行的危害;在此基础上开展了防护对策的研究,提出了向运行设备绝缘油中添加钝化剂以避免硫腐蚀发生的解决方法,介绍了钝化剂技术在华东电网500kV变压器上的具体应用情况.     

Initiation and propagation thresholds of positive prebreakdownphenomena in hydrocarbon liquids

This paper presents an experimental study of the initiation of positive streamers under step voltage in point-plane geometry, in a number of hydrocarbon liquids. The experimental conditions (point tip radius, pulse risetime, gap length) were strictly controlled in order to take valid measurements of the initiation fields and threshold propagation voltages of streamers. Transient currents associated with the initiation of positive streamers were recorded down to the μA range with a sensitive differential measurement technique. The different current shapes obtained in the liquids studied are presented. The measured inception fields of positive streamers and propagation thresholds of filamentary streamers are discussed according to the properties of the liquids (ionization potentials and mobility of charge carriers)     

Investigations of transformer oil characteristics

In this paper, the behavior of various critical parameters of transformer oil is interpreted with a view to enhancing its life time. Systems abnormalities such as excess loading, switching, and ambient conditions are responsible for the accelerated aging and sudden failure of transformer. The level of insulation plays a significant role in the life expectancy of the transformer. The diagnostics of the critical parameters for the defined ranges of aging of transformer oil attempts to determine the level of insulation and serve to ensure its efficient operation. The approach includes formulation of suggestions for determining the insulation level of the power transformer. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.