Temperature Sensing And On-line Monitoring System For Oil-Immersed Transformer Internal Winding

220kV high-voltage oil-immersed transformers work in high voltage,high current,strong magnetic field environment for long time.The aging of the insulation material directly determines the working life of the transformers.At the same time,the winding hot temperature plays a decisive role on the aging of the insulation material.So the real-time and on-line monitoring of transformer’s winding hot spot temperature is critical.In this paper,several traditional temperature measurement technologies were introduced,then the disadvantages of the current temperature measurement technologies were pointed out.Based on the rapid development of the optic-fiber temperature sensing technologies,the Ga As optical-fiber temperature sensor and on-line monitoring system for oil-immersed transformer winding was proposed.The system can precisly measure the winding’s temperature.Firstly,the temeperature sensing principle of Ga As was analyzed.As with the increase of temperature,Ga As absorbs the longer wavelength light that belongs to near-infrared band.A reflection-type optic-fiber temperature sensor was designed by using Ga As.According to Ga As’ s light absorption characteristic,the temperature sensing model was completed.Secondly,combined with the transformer’s internal complex environment,the Ga As optic-fiber temperature sensor was designed.The Ga As optic-fiber temperature sensor’s structure design,Ga As wafer’s design and the temperature probe’s packaging technology were introduced in details.The Ga As optic-fiber temperature sensor can work stably for years,as well it has the advantages such as excellent insulation and pressure performance,high reliability,good robustness,good interchangeability,small temperature probe,moderate cost.In summary,the temperature sensor is fully compatible with the transformer installation environment.Again,the on-line temperature monitoring system for the winding of the oil-immersed transformer was built.The system mainly includes the central control unit,the light source drive module,the light source group and the optical multiplexing system.In the optical multiplexing system,the light source and the spectrometer have the self-calibrating features which overcomes the wavelength drift caused by high temperature,thus can improve the temperature accuracy of the system.The hardware design of the temperature monitoring system mainly includes the design of the light source driving circuit,the interface circuit design of the central control board and the design of the spectral analysis unit.The software design is able to measure temperature accurately and in real time,and display temperature on LCD.Finally,a series of experiments were conducted to test the environmental adaptability of the Ga As optic-fiber temperature sensor and the temperature monitoring system.The results shows that the Ga As optic-fiber temperature sensor can meet the requirements of high pressure environment,and the work performance is stable.The temperature accuracy of the temperature monitoring system can reach ±2 ℃,the resolution is 0.1℃,the temperature measurement range is-20℃~150℃.At the same time,the temperature monitoring system passed the national standard certification tests and got the user authentication.