Partition And Recognition Technology Of Needle-plate Defect Partial Discharge In Oil-paper Insulation Under Combined AC-DC Voltage

The converter transformer is one of the core equipment of HVDC transmission,and its safety and reliability is the guarantee of the safety operation of the HVDC transmission system.Converter transformer valve side windings long-term withstand the role of AC-DC composite voltage,insulation problems are more complex.For ensuring the safe and stable operation of the converter transformer,it is necessary to take certain measures to realize the effective diagnosis of the insulation defect of the converter transformer.However,the current commonly used partial discharge detection due to the lack of flow control transformer operating conditions for the perfect diagnostic basis,insulation diagnosis is not ideal.The development process and discharge characteristics of typical defects of oil and paper insulation under AC-DC combined voltage can be used to provide scientific basis for the diagnosis of converter transformer defects.At present,some problems such as partial discharge stage,feature extraction and pattern recognition have been studied in some typical defects.However,as a typical representative of the oil-paper insulation defects in the very uneven electric field,the discharge of the needle-plate defects is fierce and unstable,and the discharge development characteristics have not been fully studied.To provide a more scientific basis for the evaluation of the oil-paper insulation status of the converter transformer,this paper has carried out the work from the following aspects:(1)The discharge process of the oil-paper insulated needle plate defect model was studied by the oil-paper insulation partial discharge test under combined voltage.Based on the variation rule of various feature quantities in different time periods,the process of discharge development is divided into stages,and the discharge characteristics of different development stages are analyzed and studied.(2)Under different combined voltage ratios and different temperatures,the partial discharge test of the oil and paper needle plate defects was carried out and the discharge characteristics of each stage of development were recorded.On the one hand,we can study the influence of external factors such as voltage form and temperature on the development process of partial discharge.On the other hand,it can simulate the external conditions such as different temperature and voltage forms that the converter transformer may withstand.The experiment provides sample data for diagnostic identification.(3)Feature database of.the partial discharge characteristics was constructed and appropriate characteristic parameters were extracted.The application of the support vector machine and the neural network in the identification of the partial discharge development stage of the oil-paper needle plate defect under the composite voltage were also studied,the appropriate pattern recognition method was explored to achieve the development of partial discharge of the severity of the diagnosis and identification.