Research On Inter-turn Short Circuit Characteristics Of Isolation Transformer In Power Supply Equipment

Power transformer is widely used in power system.As the critical equipment,the normal operation of the transformer is very important to the stability of the power system and the safety of the electric equipment.The large-scale power transformers are usually very expensive,and its structure is much complex.If there is a serious fault,it may take a long time to overhaul and cause serious direct and indirect economic losses.Thus,a set of sensitive and reliable protection device can be very important.The amount of the inter-turn short-circuit fault reaches 50% to 60% of the amount of the faults in large-scale power transformers.The basic principle of the isolation transformer is the same as that of the power transformer.As a preparation for the study of the inter-turn short circuit of power transformer,firstly isolation transformer is studied as an object.Isolation transformer is often applied in power supply equipment,like UPS.Thus,the study of the inter-turn short circuit of the isolation transformer do have meaning in practice.At present,many scholars have studied the inter-turn short circuit of transformer,and proposed a large number of inter-turn short circuit fault diagnosis methods,such as voltage and current ratio method,power loss method,transformer impact test method,power frequency voltage method and current ratio method based on variation,and so on,which are basically based on field test methods.A lot of scholars have deduced the variation law of the electromagnetic field in the transformer when the turn to turn short circuit occurs.At present,the correctness ratio of the generator protection and the system protection is 98.2% and 99.33% respectively.But the correctness ratio of the transformer protection is lower,because of the interference of the transformer inrush current and that the internal failure mechanism of the transformer is very complex.Therefore,the research on the characteristics of transformer inter turn short circuit is of great significance for transformer fault diagnosis and protection.In view of the above problems,this paper mainly studies the following aspects:(1)Measuring the physical parameters of the power transformer for the experiment,and establishing the corresponding model in the finite element software FLUX 3D.(2)The accuracy of the steady-state,transient and inter-layer short-circuit model is verified by comparing the measured data and the simulation data obtained by the FLUX model.(3)Several inter-turn short circuit experiments were simulated,and then the current changes in the high voltage side(HV-side)and the low voltage side(LV-side)were analyzed when the fault happens.The simulation includes: the inter turn short circuit occurs on the HV-side and the LV-side;different winding turns;different short-circuit position.(4)The numerical analysis of the internal magnetic field of the transformer during the inter-turn short circuit,which is confirmed by the results of(3),and the corresponding laws are obtained.