High-Precision Techniques of Analog Input Unit for Advanced Digital Protection Relay

Abstract

Power system control and protection equipment has required higher sensitibity and operational reliability than conventional one.
Studies of digital signal processing suitable for electric power systems fullfil this objection using fast sampling and digital filtering by a 32-bit DSP (Digital Signal Processor).
The fast sampling rate of 4.8kHz is carefully selected a point of view of A-D conversion time, operational ability of DSP for digital filter, the size of analog filter and the power spectrums of the A-D conversion output errors. The new analog input unit using a 16-bit A-D converter equipped with a recursive-type digital filter achieved high resolution of 14-bit conversion.
This paper describes the design concept and high-precision techniques of analog input unit for advanced digital protection relays. In addition, measured total A-D conversion errors filtered by the digital filters are described along with new analog filter characteristics.