A novel de-noising method based on coherence average for ultrasonic signal of partial discharge in transformer

In the developing process of ultra-high voltage oil-gas bushings prototype,the E-field distribution around the bushing end and the structure optimization of shielding electrode are important issues.We presented the basic principles and processes of hybrid algorithm which combines particle swarm optimization and back-propagation neural network(PSO-BP) in detail.The optimization capability and accuracy of the proposed algorithm were verified through a continuous explicit function.Moreover,the structure of shielding electrode was optimized using the PSO-BP algorithm.By using the PSO-BP algorithm,extreme points of the testing function could be found out exactly to jump over traps of local optimal solutions.A three-dimensional model of bushing is needed to accurately calculate the electric-field distribution around the bushing end.By using the PSO-BP algorithm,the optimum structure parameters of shielding electrode that make the maximum electric strength on the surface of the shielding electrode decreased by 64.9% is gained while reducing cost by about 75.2% than traditional PSO algorithm.The PSO-BP algorithm has been successfully applied in the manufacture of the bushing prototype.

Optimization of Shielding Electrode for UHV Oil-gas Bushings with Improved Hybrid Algorithm Combining Particle Swarm Optimization and Back-propagation Neural Network

Comparative Study on Accelerated Thermal Ageing of Vegetable Insulating Oil-paperboard and Mineral Oil-paperboard

The noise generated during transformer operation is one of the hot spots in transformer field. It is also more important to determine the position of transformer noise source based on acoustic imaging technology. This paper introduces the method and theory of transformer noise imaging, establishes transformer noise positioning system based on LabVIEW, and introduces the hardware structure and software structure of the system. LabVIEW is used to build the system, which greatly reduces the complexity of the work, and makes the system intelligent, convenient to control, real-time monitoring, with high value of use.

Transformer Noise Monitoring System

Partial discharge (PD) investigations can identify and localise incipient failures in power transformers early, thus avoiding considerable financial losses. The feature extraction of PD signals is a fundamental step for the development of such location techniques since it directly influences the performance of a location method. This study presents a detailed comparative analysis of four traditional approaches for the obtaining of attributes towards a better set of signal features for the location of PDs. The approaches were critically compared regarding their ability to locate experimentally generated discharges between adjacent layers of a prototype winding. In order to perform such analysis, a localisation structure based on logistic regression models was elaborated, capable of determining both layers and sections of the winding affected by PDs and easily applicable in practice. The results show energy features of wavelet coefficients, obtained through the decomposition of high-frequency current signals acquired at the winding endings, achieve better performance in the PD localisation, accurately indicating discharge occurrence points among layers and sections of the winding.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-smt.2020.0186

Localisation of inter-layer partial discharges in transformer windings by logistic regression and different features extracted from current signals

To investigate the effect of aging on surface discharge of the pressboard on the shielding electrode at the end of bushing, a thermal aging preparation methods of different aging degrees of pressboard samples, surface defect model, and the associated hemisphere are designed and the step-up method is used for subsequent experimental work. Finally, the partial discharges (PDs) under different degrees of aging are compared and combined with Fourier Transform Infrared spectra and electric field simulation. Results show that the pre-discharge occurs mainly in the oil gap between the hemispherical electrode edge and the pressboard. The aging of the pressboard exerts no obvious effect on the discharge characteristics in the initial stage of PD; with the development of the discharge, the development of aging of pressboard leads to a higher electric field intensity acting over a greater area, the more intense the discharge, the faster the relative discharge increases and the larger its amplitude. This discharge will cause decomposition of the oil in the pores of the aging pressboard thus generating gas bubbles which will move as discharge develops. When the bubbles reach the surface of the pressboard, the local electric field intensity will increase and the discharge will become more intense.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-smt.2018.5138

Effect of the oil-paper insulation aging on partial discharge characteristics in a hemispherical surface model

Pressboard samples with different aging degrees were prepared to study the material and discharge characteristics of pressboards with a shielding electrode. The step-up method was used for the subsequent experiment. The partial discharges of the pressboards with different aging degrees were compared and combined using Fourier transform infrared spectra, as well as electric field simulations and analysis. The microstructure of the aged pressboards was observed with scanning electron microscopy. The results showed that pre-discharge occurred mainly in the oil gap between the hemispherical electrode edge and pressboard. Aging the pressboard had no obvious effect on the discharge characteristics at the initial partial discharge stage. As the partial discharge developed, aging the pressboard resulted in a higher electric field intensity acting over a greater area, which led to a more intense discharge. Microscopic observation showed that aging and discharge destroyed the fibre, reduced the fibre width, and caused holes and fractures, which promoted further development of the discharge. The spectroscopic analysis showed that aging destroyed O-H functional groups and reduced the intermolecular forces and mechanical properties of the pressboard.

https://ojs.cnr.ncsu.edu/index.php/BioRes/article/download/BioRes_14_1_1303_Wang_Aging_Material_Properties_Discharge/6583

Xia Zhang

Papers

Effect of the oil-paper insulation aging on partial discharge characteristics in a hemispherical surface model

Effect of Aging on Material Properties and Partial Discharge Characteristics of Insulating Pressboard