Calculation And Analysis Of Temperature Rise On Converter Transformer Windings Under Variable Load

Converter transformer is the key node equipment of HVDC system.Its operation state is related to the stability of the two power grids,the sending end and the receiving end.Because there are a large number of high-order harmonics in the winding current of converter transformer,the eddy current loss of winding increases,so the total loss will be increased.Finally,the temperature rise of winding hot spot increases.The life of insulation material inside transformer is closely related to the temperature rise of winding.In order to ensure the safety of power grid and improve the operating economy of converter transformer,the research on the temperature rise of the converter transformer winding is particularly important.In this paper,first of all,the winding eddy current loss and total load loss of converter transformer at rated load are obtained by using the special software mf2 d for transformer electromagnetic field calculation and the calculation method of high-order harmonic eddy current loss specified in GB/T 18494.2.The simulation results are compared with the measured values to provide a heat source for the calculation of temperature field.A two-dimensional simplified model of converter transformer is established by using ANSYS fluent,which is a software based on the finite volume method.The loss of each coil in rated load operation is loaded into the model as a heat source,and then the temperature field is simulated.The error between the calculated result and the measured value is within4%.Based on the distribution of winding temperature field obtained by numerical method,the "integral average method" is proposed to calculate the average temperature rise of winding.The error between the calculation result of "integral average method" and the measurement result of "resistance method" is within 5%,which can meet the needs of engineering.Based on the accurate calculation of the steady-state temperature field of rated load,the hot spot temperature rise of the winding under the time-varying load of the converter transformer is calculated respectively by the analytical method and the numerical calculation method,and the accuracy of the method is verified by each other.After that,the influence of overload on the steady and transient temperature field of converter transformer winding is analyzed.Finally,it is proved by numerical calculation that changing the oil flow rate at the winding inlet of the converter transformer and using low viscosity natural ester insulating oil can reduce the temperature rise of the winding hot spot,which provides a reference for improving the overload capacity of the transformer.