Research On On-Line Monitoring Of Dielectric Loss For Transformer Bushing

The main transformer of transformer substation is the main equipment of the electric power system, the security and reliability of the electric power system is directly influenced by its reliability. In order to guarantee the safe circulate of the electric power system, the insulation monitoring of the transformer is necessarity reinforced. Bushing is one of the most important insulation parts in transformer. Therefore, the research of dielectric loss factor online monitoring of capacitance-type bushing has a high degree of theoretical significance and a great economic value.The paper pointed out the main factors influencing capacitance-type bushing dielectric loss, and then introduced the current situation of on-line monitoring situation of dielectric loss. Harmonic analysis method requires synchronous sampling for measurement signals. However, it's difficult to achieve complete synchronous sampling for the influence of power frequency fluctuation. It's the reason of spectrum leakage and fence effect. Paper analyzes the effects of spectral leakage, the reasons for the fence and analysis the role of spectrum correction. On this basis, the paper puts forward the method of harmonic analysis method based on gravity method in dielectric loss angle measurement. Compared with the traditional harmonic analysis method, this method can greatly reduce the error of synchronous sampling, and is easy to realization based on DSP. The simulation results show that the harmonic analysis method based on hanning-windowed possesses good accuracy, real-timing and anti-interference characteristics.Because the angle error of PT have a big influence on the on-line monitoring of Dielectric loss, this paper analyzed the influence factors of the angle error of PT, and puts forward some solving measures. In this paper, the algorithm for calculating the angle error of PT is studied and improved. Without increasing hardware, this algorithm can be used in on-line monitoring system. Simulation results show that this algorithm has accuracy and can effectively reduce the impact of the angle error of PT on the calculation of tanδ.On the basis of theoretical analysis, this paper designed a set of on-line monitoring system for capacitance-type bushing. This system adopts layered distributed structure, PC is located in the field of computer control indoor unit, On-site measuring unit adopts digital signal processing (DSP) TMS320F2812 as chip processor. This paper introduces the software structure of the system and the division of modules, and illustrates the function of each software module and realization method.