Robust Analog DC Isolator for Cathodic Protection Applications

Abstract

To provide cathodic protection (CP) for gas and oil underground pipelines, a direct current (DC) isolator is needed to isolate the main CP converter from the earth around the pipeline. The DC isolator, proposed in this paper, consists of four parts: a second-order low-pass active filter, voltage level shifter, pulse-width-modulation (PWM) controller, and a ground isolator. This converter is designed to accurately provide an isolated near-ground voltage as a control input of the main CP converter in harsh outdoor environments, which is its privilege in comparison with other solutions. The second-order low-pass active filter is designed to filter possible disturbances in the vicinity of the pipeline and reduce the loading effect of the permanent half-cell resistor. The voltage level shifter provides proper voltage range and increases the precision of the main CP converter. The PWM controller is used to provide alternating current (AC) voltage for ground isolator, and the ground isolator provides enough isolation from the dirty ground near the pipeline. Finally, a prototype is implemented and tested to verify the theoretical and simulation results.