Research On Measurement Technology Of High Voltage Current Based On Optic-electrical Current Transformer

CT is an important equipment of power system, which plays an important role in the measurement protection and monitoring of power system. With the development of voltage level of China’s power grid, the electromagnetic current transformer, which is widely used in the current power system, exposed insulation structural complexity, high cost, bulky and other issues. It will greatly restrict the intelligent, network-based development of the power system that conventional current transformers can only output analog signals, which cannot match the digital communication system. Optic-electrical Current Transformer(OECT), which incorporates advanced photonics technology and optical communication technology, can overcome the shortcomings of conventional transformers. It will replace the traditional current transformers, and become the main measuring device for high-voltage and large current in power system.In this paper, the research and analysis of the measurement of high-voltage current by Active Optical Current Transformer based on Rogowski coil and voltage-frequency conversion technology is conducted, and the model of relationship between the analog current input and the digital frequency output is established. This design uses the Rogowski coil as a sensing head to sample the measured high-voltage current. Then the sampled signal is converted to an optical pulse signal by V/F converter and E/O converter,and then transmitted to the signal processing section in low pressure side via the optical fiber transmission. Power supply is transmitted through the fiber probe from low pressure side to high pressure side to provide a stable power. By the two-fiber way to transmit the sampled pulse signal and power, the electrical isolation between the high and low voltage side is effectively solved. The pulse frequency signals are counted in the low pressure side to give a digital output.In order to obtain the optimal design, this paper carried out a detailed comparison and analysis of several plans of the design of the sensor head, digital signal processing, energy supply system and other parts. Laser power supply scheme is proposed, which is based on a series or parallel photodiode(PD), improving the conversion voltage that can meet theneeds of the converter probe circuit.Through the analysis of experiments and simulation results, it is verified that OECT is with high accuracy and strong anti-jamming ability, etc., and has broad application prospects.