Research On Dynamic Stability Analysis Of Power Transformer Windings Based On Cumulative Effect

With the construction and development of China's Energy Internet,UHV power grid plays an increasingly important role in China's power supply.As a key equipment of power transmission and conversion in power grid,power transformers are unavoidably subjected to impact of the short-circuit current during operation,their ability to withstand short-circuit current is related to the safety factor and operational sustainability of the entire power grid and themselves.The calculation of dynamic stability of power transformer windings under multiple short-circuit electromagnetic load is a multidisciplinary comprehensive problem involving electromagnetism,mechanics and materials science,it needs to synthetically consider the related knowledge of various disciplines and then apply related knowledge to the accurate calculation of the dynamic stability under the short circuit of the power transformer,which is a practical issue with great value and difficulty.This paper summarizes the domestic and international research status of electromagneticfield,short-circuit strength and cumulative effect of short circuit electromagnetic force and the calculation methods and research results of related issues firstly.According to the basic mechanism of cumulative effect of transformer windings under short-circuit electromagnetic load,different phase winding's leakage magnetic flux distribution,electromagnetic load distribution of the three-phase three-legged transformer in different short-circuit conditions are analyzed by the finite element simulation software then.Finally the short-circuit strength and cumulative effect of the medium-voltage winding of different phases are calculated by the finite element magnetic-structural direct coupling method.And the law of short-circuit transient temperature rise,partial stay failure and axial pre-tightening force on the cumulative effect of winding short-circuit is summarized at the same time.Based on the calculation model of transformer three-dimensional magnetic field and taking into account the magnetic field distribution of transformer winding affected by the core,the comparison and analysis of the leakage magnetic field distribution of a three-phase three-legged transformer in single-phase short-circuit and three-phase short-circuited condition of each zero-crossing phase winding are carried out,and an experimental platform with the model transformer is built to compare the measured value with the calculated value;Then a three-phase three-legged power transformer model suitable for the magnetic-structural direct coupling method is established,and the electromagnetic load distribution and the single short-circuit response of different phase the medium voltage windings are calculated and analyzed.On this basis,the material mechanical properties of the copper conductor wire are studied,and the material mechanical model of the copper wire suitable for the calculation of the cumulative effect is proposed,to calculate the short-circuit cumulative effect of different phase middle windings under three-phase short-circuit condition and a stability criterion applied to the check of cumulative effect is summed up.And the influence law of various factors that may affect the cumulative effect of winding short circuit is calculated and summarized,and then some effective measures for improving the resistance to the cumulative effect of power transformer windings are put forward.The research in this paper has certain practical value to the short-circuit stability check and design improvement of the transformer.