Experimental Research And Program Development Of Short-circuit Withstand Capability Of Power Transformers

Due to the design,manufacture and maintenance of power transformer,short-circuit damage often occurs in the operation of power system,which will lead to large area blackout.Its maintenance period often takes several months,causing huge losses to power grid and users.In this paper,a 40MVA/110 kV three-phase three-winding is used as a test model to study the short-circuit strength of transformer under HV-MV and HV-LV conditions,and the real short-circuit current tolerance value of the transformer is obtained.On the basis of the test,a software of transformer winding short-circuit strength checking is developed to improve the level of transformer short-circuit resistance design,guide transformer short-circuit resistance checking,and ensure the operation quality of transformer.Firstly,the calculation principle of transformer’s short circuit resistance is described.This paper mainly introduces the calculation principle of transformer short-circuit current,including the calculation and analysis of steady-state and transient short-circuit current of double windings and three windings,analyzes the calculation of short-circuit electrodynamic force of transformer windings from radial and axial directions respectively through the distribution of leakage magnetic field,and expounds the checking and evaluation of transformer short-circuit resistance ability.On the basis of the main characteristics of winding damage,this paper analyzes the radial strength,axial strength,insulation material strength and plate strength,and introduces the calculation principle of winding thermal stability briefly.Secondly,on the basis of basic parameters and structure,the dynamic and thermal stability of transformer is calculated in detail,and the short-circuit current tolerance values of each winding are given;the short-circuit impact test scheme of transformer is introduced;the test contents and test results of HV-MV and HV-LV short-circuit conditions are expounded emphatically.After the test,each winding of the transformer is disintegrated and analyzed,and the yield strength of each winding conductor is tested.Based on the test data and disintegration analysis,the test is summarized and analyzed.Thirdly,on the basis of introducing the characteristics of VB language,the calculation process and development content of winding short-circuit strength checking program are mainly introduced.The main contents of software development include: short-circuit current calculation,short-circuit electromotive force calculation and winding short-circuit strength checking.Finally,taking the test product as an example,the short-circuit strength of the transformer winding is checked.The results show that the accuracy of the program is high.Finally,the results of the experimental research and software application on the anti-short circuit ability of transformer in operation are summarized,and the future research prospects are prospected.