Wu Gaolin

Discussion on Condition-based Maintenance for Electric Equipments in Chongqing Electric Power Corporation

With the development of testing and producing technology, condition-based maintenance become more and more popular and inevitable for electric equipments, because of its high reliability and efficiency. And some research about condition-based maintenance has been done for a long time in Chongqing electric power corporation. In this paper some of our research will be shared and discussed. Condition evaluation is the foundation of condition-based maintenance, and on-site testing is the main way to know the condition of equipments at present. The method to evaluate the condition of equipment will be introduced in this paper, depending on the testing data. So a new regulation about maintenance and testing of equipments is necessary, in order to regulate the testing and evaluation for electric equipments. The main idea of this regulation will be presented in this paper. According to the regulation, a software of condition-based maintenance information management system has been programmed, using MSSQL server database, and that this system runs at browser/server mode. This system can synthetically analysis the different information that show the conditions of electric equipment, including testing data, family fault, bad working state and give the evaluation of equipment with numerical value. With the publication of regulation and deep application of the system (CMIMS), the condition-based maintenance would be popularized in the Chongqing grid.

Influence of oil property on the space charge characteristics and electric field distortion in oil-paper insulation

The formation of space charge in oil/paper insulation system can lead to material degradation in the high electric field region and affect system reliability. It is important to understand factors that affect space charge formation in oil/paper insulation system. All the researches on the space charge characteristics of oil-paper insulation are all based on the oil impregnated insulation paper. In this paper, the space charge dynamic behavior of the oil impregnated insulation pressboard and the mixed insulation with a combination of oil gap and oil impregnated insulation pressboard were both studied. The oil property effect on the charge and electric field distribution behavior were discussed. The injected charge in aged oil impregnated insulation pressboard has a higher migration rate than that in new oil impregnated insulation pressboard. Compared with the oil impregnated insulation pressboard, a lot of space charges accumulate at the interface between oil and pressboard, which leads to obvious electric field distortion in oil gap and in oil impregnated insulation pressboard. The charge injected in new oil-paper insulation is more difficult to dissipation than that in aged oil-paper insulation.

Space charge characteristics of oil impregnated insulation paper under the power frequency voltage

Space charge characteristics of insulating materials under AC voltage and DC voltage are equally important. There is a huge amount of AC transformers in the power transmission system. However, there is no report about the space charge characteristics of the oil-paper insulation materials under the AC voltage. In this paper, firstly, the space charge characteristics of the oil immersed insulating paper under the positive/negative DC field were investigated using the pulsed electro-acoustic (PEA) method. Secondly, the space charge characteristics of the oil immersed insulating paper under power frequency voltage were studied using the improved PEA system. Results show that the electric field polarity has a decisive impact on the charge distribution. When the DC electrical field is positive polarity, the polarity of the charge accumulated at the paper-paper interface near the aluminum electrode is positive, while it is negative when the DC field strength is negative. The charge polarity of the charge accumulated at the aluminum electrode is negative in the positive half cycle under the power frequency voltage. It is positive in the negative half cycle of the power frequency voltage. The charge polarity of the charges accumulated at the internal interface of the oil-immersed insulation paper are opposite for 90° and 270° phase in the voltage applied process. The charges accumulated within the oil-immersed insulating paper under the power frequency voltage show a significant reduction compared with the results under DC voltage.

A new method to identify the material of transformer winding

Copper and aluminum, different in electric and mechanical properties, are the main marterial of the internal winding of the transformer, there, nevertheless, is a loss of effective method to identify them unless destroying the insulation. To solve the problem, a test platform is established with an effective and nondestructive method based on Seedback effect is provided in this paper to mesure the tempratural difference between head and terminus of the winding and the thermoelectric potential of the cuircuit to identify the internal marterial. The simulational and experimental results demonstrate the effectiveness of the method.

Space charge characteristics of oil gap and pressboard mixed insulation based on the pulsed electro-acoustic measurement

There are many researches about the space charge behavior of solid insulation (oil immersed insulation paper/pressboard) in transformer based on the pulsed electro-acoustic (PEA) technique. However, no research on the space charge behavior of the oil-paper insulation system consisted by oil gap and oil immersed insulation pressboard was conducted. The space charge characteristics of the oil immersed insulation paper, the mixed insulation consisted of oil gap and pressboard were investigated using the PEA Measurement System. The space charge accumulation behaviors at the interface between oil gap and pressboard were analyzed. The distortion of the electrical field in the oil gap and pressboard was also analyzed. Results show that there are many charges injected into the oil and the pressboard. The charges accumulated at the interface between oil gap and pressboard increases with the electric filed applied. The electrical field distortion is obvious with the applied electric filed for the sample with 0.68% moisture content. While the charges accumulated in the mixed insulation system with 3.83% moisture content become less with the conductivity increased, as well as the electrical field distortion.

Influence of oil property on space charge dynamics in oil-paper insulation under DC and AC electric field

Space charge in oil/paper insulation has a close relation to its electrical performance. Space charge characteristics of insulating materials under AC voltage and DC voltage are equally important. There is a huge amount of AC transformers in the power transmission system. However, there is little report about the space charge characteristics of the oil-paper insulation materials under AC voltage. In this paper, firstly, the space charge characteristics of the oil immersed insulating paper with different oil property under the positive/negative DC electric field were investigated using the pulsed electro-acoustic (PEA) method. Secondly, the space charge characteristics of the oil immersed insulating paper with different oil property under power frequency voltage were studied using the improved PEA system. Results show that oil property has an obvious impact on the charge distribution. The more the deterioration of the oil, the larger amount of charges injected into the oil impregnated insulation paper. The charges accumulated within the oil-immersed insulating paper under the power frequency voltage show a significant reduction compared with the results under DC voltage.

CaCu 3 Ti 4 O 12 陶瓷深陷阱松弛特性研究

研究了固相反应法及共沉淀法制备的CaCu 3 Ti 4 O 12 陶瓷深陷阱松弛特性. 测试了CaCu 3 Ti 4 O 12 陶瓷在频率为0.1~10 7 Hz, 温度为–100~100℃的范围内的介电频谱及温谱. 通过对不同温度下介电频谱的分析, 研究了双Schottky势垒结构中深陷阱松弛特性. 研究表明：在交流小信号作用下, 由于Schottky势垒中深陷阱与Fermi能级的上下关系发生变化, 引起深陷阱电子发射和俘获即电子松弛过程, 在介电频谱中表现为松弛峰; 并且由介电谱的分析结果可得深陷阱能级等微观参数. 比较不同试样的深陷阱参数可知：在CaCu 3 Ti 4 O 12 陶瓷中, 在导带以下约0.52和0.12 eV的能级处存在由本征缺陷产生的深陷阱. 介电温谱与频谱的分析类似, 二者可以互为补充.研究了固相反应法及共沉淀法制备的CaCu 3 Ti 4 O 12 陶瓷深陷阱松弛特性. 测试了CaCu 3 Ti 4 O 12 陶瓷在频率为0.1~10 7 Hz, 温度为–100~100℃的范围内的介电频谱及温谱. 通过对不同温度下介电频谱的分析, 研究了双Schottky势垒结构中深陷阱松弛特性. 研究表明：在交流小信号作用下, 由于Schottky势垒中深陷阱与Fermi能级的上下关系发生变化, 引起深陷阱电子发射和俘获即电子松弛过程, 在介电频谱中表现为松弛峰; 并且由介电谱的分析结果可得深陷阱能级等微观参数. 比较不同试样的深陷阱参数可知：在CaCu 3 Ti 4 O 12 陶瓷中, 在导带以下约0.52和0.12 eV的能级处存在由本征缺陷产生的深陷阱. 介电温谱与频谱的分析类似, 二者可以互为补充.