Stress Analysis And Research On Winding Faults Of Dry-Type Transformer

With the development of offshore oil platforms,the stable operation of their power systems is becoming more and more important,The epoxy resin cast dry-type transformer is an important link in the power supply and distribution system of offshore oil platforms,and there are few opportunities for power outages.Therefore,reducing the failure probability of transformers is important to improving the reliability of the power system.Winding fault is one of the common faults of transformers,even minor winding faults can lead to serious consequences.At present,most researches focus on oil-immersed transformers,but the research on winding faults of dry-type transformers has not attracted enough attention.This paper researched on the thermal stress,mechanical stress and winding fault diagnosis methods that cause dry-type transformer winding faults considering the structure and characteristics of dry-type transformers used on offshore platforms.The main research contents of the paper are as follows:(1)The finite element model of epoxy resin cast dry-type transformer is established and thermal stress analysis is studied:analyzed the theory of heat conduction and thermal stress,established a field-circuit coupling finite element model,and calculated the results of different working conditions to verify the accuracy of the model;Calculate the thermal time constant of the transformer,analyze the thermal stress under various working conditions,and obtain the characteristic that the thermal stress is proportional to the square of the current.It is concluded that the thermal stress mainly causes the radial and axial expansion and deformation of the winding and the thermal stress has an effect on the epoxy resin.The conclusion that the influence is greater than the winding;the operation and maintenance guidance is given from the perspective of the influence of thermal stress on the life of epoxy resin.(2)The effect of mechanical stress on epoxy resin cast dry-type transformers is studied:the mechanism of mechanical stress is introduced,the generation and types of transformer electromagnetic force are analyzed;the electromagnetic force of windings is calculated on the basis of electromagnetic finite element analysis.The electromagnetic force and the distribution on the winding are calculated and summarized rules to verify the principle;the modal analysis is used as the basis of the stress analysis,and the feedback effect of the transformer structure on the electromagnetic force of the winding is investigated;the winding strength is calculated and analyzed The ability of the winding to bear stress;the mechanical stress is analyzed using electromagnetic force structure coupling,and the mechanical stress of the transformer under normal,overload and three-phase short-circuit fault conditions is analyzed,and the characteristic that the mechanical stress is proportional to the square of the current is obtained,and the stress concentration is analyzed The law and its influence on winding deformation;the transient changes of winding insulation life and winding deformation under the influence of stress are analyzed.(3)The method for diagnosing minor winding faults using the currents on both sides to calculate the short-circuit impedance is studied:first,the method of calculating the short-circuit impedance is introduced and the reliability of the algorithm is initially verified,and then the online calculation using the currents on both sides and considering the change of the excitation current and the relevant characteristic quantities for the identification of inter-turn short-circuit faults is extracted;finite element analysis to simulate various winding deformations of transformers including inter-turn short-circuit faults and use algorithms to calculate the change trend of short-circuit impedance caused by deformation Analyze and discuss the degree and degree;when the transformer winding deforms,the short-circuit impedance change becomes larger with the degree of deformation.When the axial displacement or radial expansion deformation,the short-circuit impedance change is greater than the radial displacement deformation;short circuit between turns Under the circumstances,the transformer short-circuit reactance changes greatly,in which the high and low voltage windings change in the opposite direction,and the inter-turn short-circuit fault characteristic quantity changes greatly in the case of inter-turn short-circuit,indicating that this feature can be effectively used to detect and identify minor inter-turn deformation faults.