Monitoring And Application Of Hot Spot Of Transformer Winding Based On Fiber Optic

Oil-immersed power transformer is one of the most widely used power equipment in the power grid.The life of the transformer is determined by the internal insulation materials,most of which contact with the copper directly.And the copper for winding is one of the main heating element inside transformer.Failure will occur if the internal temperature is too high,and it leads to transformer failure,power grid collapse,or huge economic loss and safety problems.Therefore,the correct and timely feedback of the hottest temperature rise of transformer windings has great significance on preventing the local overheating of transformer.The traditional winding hot spot temperature is measured by a thermometer,which includes top oil temperature and copper to oil temperature.However,the error of this method is relatively large.In this paper,a method of measuring the hot spot temperature of the winding with optical fiber is proposed.The advantage of fiber optic method is that the measurement error is only within ±2℃,which means the accuracy is higher.A 150 MVA/220 kV transformer is taken as the research object.Two kinds of methods to calculate winding temperature: engineering calculation method and temperature field simulation calculation method are used.The difference between them is presented.The key problem of fiber used in transformer is to determine the most hot spot of the winding.According to the different eddy current loss distribution caused by the leakage magnetic field of the winding,this paper studies the eddy current loss of the winding from the axial direction,radial direction and circumferential direction respectively.In order to verify the analytical and calculated results,the optical fiber probes were installed in different parts of the windings in different phases(one for each phase in HV and MV winding).The final experimental results are in line with the predicted position,and the error is also within the allowable range of the project.Therefore,it is feasible to use optical fiber to measure the temperature inside the transformer.At the same time,the data measured by optic fiber was compared with those obtained by the traditional resistance method.The maximum error is 9.4%,which indicates that the traditional method of measuring the winding hot spot has great limitations.Lastly,the reason of the error is analyzed in this paper.The experience obtained in this paper has reference value for the future use of optical fiber temperature measurement to monitor the hot spot temperature of winding online.