Design Of Low-frequency Short-circuit Heating Device For Transformer

Power transformer is one of the most important parts of the electrical power systems,the security and efficiency of the power transmission are affected by the operating state of power transformers,and the moisture of transformer is one of the most important factors that impact the safe operation of the power transformers.Therefore,dry the transformer is essential.The traditional hot oil circulation method using vacuum oil filter has the disadvantages of low efficiency and long cycle,and the effect is not obvious in the low temperature climatic environment.Power frequency short-circuit heating method also has many shortcomings such as large volume,great weight,complex composition and high voltage,and it is not applicable for site.Therefore,it is of great significance and application value to explore a simple and efficient method of heating and drying transformer.In this dissertation,the technical background and development of drying of transformer are analyzed and introduced.Then the principle of moisture in the transformer is analyzed.On this basis,the low frequency short-circuit heating method of transformer is put forward.The influence of frequency on the low frequency short-circuit heating device is deduced.The safety and heating capacity of low frequency short-circuit heating method are analyzed theoretically.Based on PWM control technology,using DSP28335 as the main control chip,designed the transformer low frequency short-circuit heating device,including the overall design of the system,the design of main circuit structure,the design of control circuit,the design of load current detection system and the design of transformer winding hot spot temperature monitoring system,designed the software part of the system and completed the production of the device.Finally,the output waveform of the device was tested,and the relationship between the frequency and the voltage,capacity and power factor of the heating power source is tested,then simulation of large-scale power transformers,made a short-circuit heating model test.Through the results of the test we can found that,the voltage and capacity of the heating power supply are reduced and the power factor will increase in the case of constant output current.The results show that the low frequency short-circuit heating method can improve the heating and drying efficiency of the transformer and reduce the volume and weight of the heating device,thus enhancing the mobility of the heating device,suitable for outdoor drying of large scale power transformers.