Research On The Application Of Giant Magneto-Resistance Sensor In DC Current Detection

As the rapid development of high voltage direct current(HVDC) transmission network in China, the electric power industry is facing more challenges come from the computer technology and other new technologies, which make the traditional DC current transformer(CT) can't fulfill the further development of the power system. Therefore, the CT which owns the excellences of intelligent, digital and small size is urgently needed. According to the comparison on different principles of DC measurement, this paper adopts giant magneto-resistance (GMR) sensor to measure the magnetic field intensity in the iron core's air gap, so the current value can be gained.By comparing the cost and measurement accuracy of the open-loop and closed-loop CT, this paper adopts the open-loop CT as the research direction. The relationship between the exciting current and the magnetic field intensity of the iron core's air gap is calculated by the finite element software, and the saturation problem of this iron core is solved perfectly. The iron core's material and size can also be determined by the calculation results. According to these results, a CT whose rated current reaches 3000A is designed. Through the analyses of GMR sensor's technical parameters, which conclude the input and output characteristics, the temperature characteristics, the magnetic hysteresis reaction and the angle of magnetic sensitive axis, the sensor's linearity range is determined. According to these analyses, a CT whose range is between 0 and 400A has been designed. The experimental results prove that the linearity of this CT is superior to 0.5%, which has achieved the original design target. Furthermore, the power supply and anti-interference characteristic of this CT are discussed.