Combined Power Supply System For Electronic Current Transformer

Current transformers play an important role as a kind of high-voltage equipment in power system. It is applied in the relay protection, system metering and analysis of power system. With the development of power system towards higher voltage, higher capacity and digitization, it is different for the electromagnetic current transformers to keep up with the development of power system. Therefore, it is an inevitable trend to research a new kind of current transformer for high accuracy measurement such as electronic current transformer (ECT) which based on the technology of computer, communication and DSP. Power supply for those active electronic elements at the high-voltage part is a key technique in high ECT system.In this paper, the development of electronic current transformer at home and abroad is described, and the realized ECT power supply schemes are summarized. Based on the characteristics of ECT which is developed in our laboratory, a new power supply system combined with the self-supplying power source and the optical in ECT is proposed.Firstly, an optical power supply with digital circuit technology for high voltage ECT designed in this paper, which includes the driving, protecting and thermal-controlling circuit of high power laser with MCU MSP430, the input and display circuit, and voltage converter on high-voltage terminal. After the optical battery transfers the light power to electronic power that generate by laser source, the sensor of ECT can be supplied well. The experimental results show that a +6V voltage and more than 300mW power is supplied.Secondly, this paper introduces a design of power supply source applied for electronic system in high voltage. The energy is obtained directly from the power line by some tailor-made current transformer (CT). By setting an inductance in series with the CT and the rectifier bridge, the voltage on the rectifier is reduced to the acceptable level and the output current from the CT is also limited to very small. Thus, the inductance helps to steady the voltage and protect the follow circuit. The experimental results show that a +5V voltage is supplied, whose ripple is less than 25mV.Finally, a power supply is proposed which is combined of the self-supplying power source and the optical, and the switch technique between the two supplies is provided in the paper. The dead area is got rid of in the self-supplying CT power source and the lifetime of the optical power supply is improved.