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6. Field Experiences on Oil Ageing Characteristics of Transformer On-Load Tap Changers

Author

Jiang Shuo, Xian Yang, Jiang Danyu, Zhou Dan, and Ma Zhiqin

Subjects
Leak, Materials science, Petroleum engineering, 010405 organic chemistry, Group composition, 010402 general chemistry, 01 natural sciences, Tap changer, 0104 chemical sciences, law.invention, Field experience, law, Breakdown voltage, Research Object, Transformer, Water content
Abstract

On-Ioad tap changer (OLTC), extinguishing arc with oil, is one of the important components of transformer. Combined many years of field experience, physicochemical properties and electrical properties of oil deteriorate under the combined action of electric, thermal and mechanical agitation. Taking the oil for OLTC in 110kV transformers as research object, ageing characteristics of oil in different operation periods, such as water content, breakdown voltage and oil group composition, were studied comparatively. The results show that the decrease of breakdown voltage is determined by the water content in oil, operation time and operation times of OLTC. Furthermore, the low content of aromatic carbon in the oil is also cause the breakdown voltage to decrease obviously, but the change of water content is small. The water content undulates during operation. The leak of sealed for OLTC is the main factor that makes the breakdown voltage and the water content greatly change.

Published
2020

7. Research on Fault Diagnosis of Oil-Paper Insulated Bushing Based on Frequency Domain Dielectric Spectrum

Author

Xian Yang, Jiang Danyu, Ma Zhiqin, Jin Yuhui, Cai Linglong, and Shu Xiang

Subjects
Materials science, Dielectric spectrum, law, Bushing, Electrical equipment, Frequency domain, Acoustics, Fault (power engineering), Transformer, humanities, Radio spectrum, Dielectric spectroscopy, law.invention
Abstract

As an important component of power transformer, transformer bushing cause thirty percent of transformer accidents. It is difficult to find defects in transformer bushing in advance because of the lack of on-site inspection methods. Frequency domain dielectric spectroscopy is widely used in the field of insulation evaluation of electrical equipment because of its frequency bandwidth and rich information. However, the frequency domain dielectric spectroscopy in the inspection of oil-paper insulated transformer bushing is affected by lacking substation test case and diagnostic criteria. In this paper, a dielectric response model of the transformer bushing is established to reveal the different defect types corresponding to the test curves in different frequency bands. In the low frequency band which is less than 0.0lHz, it is reflecting the water content of bushing. In the middle frequency band which is between 0.0lHz to 100Hz, it is reflecting the aging of bushing. Several cases of substation bushing defects detected by frequency domain dielectric spectroscopy have verified the above results. It is difficult to propose uniform fault diagnosis criteria for the frequency domain dielectric spectrum of transformer bushing which is affected by the structure and type. Based on a large number of substation case studies, a defect diagnosis criterion based on Frechet similarity method is proposed in this paper, which is universal for different structures and different types of bushing.

Published
2020

9. Experience Gained in Fault Diagnosis and Tear-down Analysis of Transformer Bushings

Author

Cai Linglong, Zhou Dan, Lin Chunyao, Ma Zhiqin, Ouyang Xudong, Ou Xiaobo, and Xian Yang

Subjects
Computer science, law, Frequency domain spectroscopy, Bushing, Dissolved gas analysis, Partial discharge, Diagnostic test, Key features, Transformer, Reliability engineering, law.invention
Abstract

As an essential component of power transformer, transformer bushing’s reliable operation does not only impact the safety of transformer itself but also other equipment located nearby. To prevent bushing failures, it is therefore important to routinely assess bushing insulation and pin-point the potential problem as early as possible. In this paper, fault diagnosis and tear-down analysis of five 500kV oil-impregnated paper (OIP) transformer bushings are presented. Results of different field and laboratory diagnostic tests are discussed and compared. Key features of partial discharge-led defect with x-wax deposits are analysed. The effectiveness of adopting frequency domain spectroscopy (FDS) in combination with dissolved gas analysis (DGA) as supplementary field diagnostic test is then demonstrated.

Published
2019

10. Internal Oil Flow of Transformer Based on Multiphysics Coupling Characteristic Analysis

Author

Ma Zhiqin, Jiang Danyu, Xian Yang, Zhou Dan, and Jingli Dou

Subjects
Computer simulation, Computer science, business.industry, Inner core, Mechanical engineering, Gas protection, Multiphysics coupling, Magnetic field, law.invention, Electric power system, Software, law, Transformer, business
Abstract

The misoperation of gas protection in transformer out-of-zone faults will seriously affect the security and stability level of power system. In this paper, the oil flow characteristics in transformer under different operating conditions are analyzed by multi-physical field coupling simulation. The principle of common gas protection relays and their causes of misoperation are analyzed. A numerical simulation model of multi-physical field inside transformer is established. The inner core and winding of transformer are modeled and simulated by ANSYS Maxwell 3D and ANSYS Fluent software. The variation of multiphysical field in normal operation, out-of-zone fault and in-zone fault of transformer is obtained. The changes of magnetic field and electromagnetic stress, oil flow and outlet pressure of inner winding and core of transformer are analyzed. This study provides a new basis for formulating measures to improve the reliability of gas protection operation.

Published
2019

14. Quantitative analysis of insulation condition of oil-paper insulation based on frequency domain spectroscopy.

Author

Liao, Ruijin, Liu, Jiefeng, Yang, Lijun, Wang, Ke, Hao, Jian, Ma, Zhiqin, Gao, Jun, and Lv, Yandong

Subjects
INSULATING materials, QUANTITATIVE research, PARAMETER estimation, ENERGY dissipation, POLYMERIZATION, MOISTURE, TEMPERATURE measurements
Abstract

In order to distinguish the influences of moisture and aging on the frequency domain dielectric response of oil-paper insulation and better apply frequency domain spectroscopy (FDS) to assess the insulation condition of power transformers, the oil-paper insulation samples with different moisture contents and different aging states were prepared in the laboratory. The FDS of the samples were tested and a group of characteristic parameters were extracted from dissipation factor (tan?) curves which could be used to assess the moisture content and aging states of oil-paper insulation respectively. The quantitative relationship among characteristic parameters, degree of polymerization (DP) and moisture contents (Km.c) was accurately established. The observations show that the proposed characteristic parameters are sensitive to the moisture in 10-3-102Hz, while the aging states influence the characteristic parameters in 10-3-10-1Hz. Meanwhile, an exponential relationship equation which could be used to assess the oil-paper insulation condition was established among the characteristic parameters, DP and the moisture content. Finally, the evaluation technique proposed in this paper was used to diagnose the insulation condition of several field transformers in this way, and its validity was preliminary and reasonably verified. [ABSTRACT FROM AUTHOR]

Published
2015
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15. Quantitative analysis ageing status of natural ester-paper insulation and mineral oil-paper insulation by polarization/depolarization current.

Author

Hao, Jian, Liao, Ruijin, Chen, George, Ma, Zhiqin, and Yang, Lijun

Subjects
QUANTITATIVE research, ESTERS, ELECTRIC insulators & insulation, MINERAL oils, POLARIZATION (Electricity), ELECTRIC currents, PHYSICS experiments, TEMPERATURE effect
Abstract

Polarization and Depolarization Current (PDC) technique is an effective tool to assess the condition of oil-paper insulation system in power transformers. So far the PDC behaviors of mineral oil-paper insulation have been widely investigated. However, with the increasing number of transformer choosing natural ester as its insulation oil, it is important to investigate the PDC characteristics of natural ester-paper insulation to see whether the PDC technique can also be used to assess the condition of new insulation system using natural ester in transformers accurately. In this research, natural esterpaper insulation sample and mineral oil-paper insulation sample were subjected to thermally accelerated ageing experiment at 110°C for 120 days. The PDC characteristics of natural ester-paper insulation sample and mineral oil-paper insulation sample were compared over the ageing process. A new method for assessing the ageing condition of the oil-paper insulation in terms of the depolarization charge quantity was proposed. Results show that the polarization/depolarization current of natural ester-paper insulation sample is higher than that of mineral oil-paper insulation sample with the same ageing intervals. The depolarization charge quantity of both kinds of oil-paper insulation sample is very sensitive to their ageing conditions. There is an exponential relation between the stable depolarization charge quantity of both kinds of oil-paper insulation sample and the degree of polymerization (DP) of paper. The depolarization charge quantity can be used to predict the ageing condition of oil-paper insulation providing the measurement temperature is kept the same. [ABSTRACT FROM PUBLISHER]

Published
2012
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16. A comparative study of physicochemical, dielectric and thermal properties of pressboard insulation impregnated with natural ester and mineral oil.

Author

Liao, Ruijin, Hao, Jian, Chen, George, Ma, Zhiqin, and Yang, Lijun

Subjects
DIELECTRICS, THERMAL properties, ELECTRIC insulators & insulation, MINERAL oils, ESTERS, COMPARATIVE studies, ELECTRIC breakdown
Abstract

Natural ester is considered to be a substitute of mineral oil in the future. To apply natural ester in large transformers safely, natural ester impregnated solid insulation should be proved to have comparable dielectric strength and thermal stability to mineral oil impregnated solid insulation. This paper mainly focuses on a comparative study of physicochemical, ac breakdown strength and thermal stability behavior of BIOTEMP natural ester/pressboard insulation and Karamay 25# naphthenic mineral oil/pressboard insulation after long term thermal ageing. The physicochemical and dielectric parameters including moisture, acids and the ac breakdown strength of these two oil/pressboard insulation systems at different ageing status were compared. The permittivity and ac breakdown strength of these two oil/pressboard insulation systems at different temperatures were also investigated. And a comparative result of the thermal stability behavior of these two oil/pressboard insulation systems with different ageing status was provided at last. Results show that though natural ester has higher absolute humidity and acidity during the long ageing period, the lower relative humidity of natural ester helps to keep its ac breakdown strength higher than mineral oil. The pressboard aged in natural ester also has higher ac breakdown strength than that aged in mineral oil. The lower relative permittivity ratio of natural ester impregnated paper to natural ester is beneficial to its dielectric strength. Using natural ester in transformer, the resistance to thermal decomposition of the oil/pressboard insulation system could be also effectively improved. [ABSTRACT FROM AUTHOR]

Published
2011
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