Optical Electric Current Transformer for Monitoring Its Performance in the Substation

Abstract

The optical electric current transformer (OECT) is an important measuring and protection equipment in the power system. Its accuracy and reliability are vital to the power system’s safe, reliable, and economical operation. Because the energy supply of a high-voltage side data acquisition system is the biggest obstacle in developing this kind of transformer, a low-power data acquisition system of OECT is designed from cost, reliability, accuracy, and practicability. In the design process, the low-power microcontroller MSP430 produced by TI company is used for control. Its rich on-chip and off-chip function modules and ultra-low power performance meet the system’s requirements. The 16-bit low-power high-speed chip ADS8325 is used as an A/D converter to ensure the instantaneity and accuracy of data acquisition and the low-power characteristics of the system. The optical fiber digital transmission system is utilized to achieve high/low voltage electrical isolation, and the low-power optical fiber transmission drive circuit is devised. After the main hardware design is completed, the software is adjusted and used in the electric energy monitoring of the substation. The test shows that the error of three-phase current and three-phase voltage is less than 2%. After setting the voltage amplitude, current amplitude, and power factor, the error of its active and reactive power is less than 2% after electric energy monitoring. After multiple harmonic tests, the measurement errors of voltage harmonics and current harmonics are smaller than 5%, that is, the measurement results of each index achieve high measurement accuracy.