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The Effect of Inductive Loading on Rectifier Interruption

Direct current (DC) sources are a critical component of many cathodic protection (CP) systems. In order to assess the performance of these CP systems, momentary interruption of the DC current output is often utilized to help obtain true polarized potentials of protected structures1. This is achieved with a relay that is either integral to the DC current source or installed externally. Traditionally, these relays use a mechanical or mercury contactor, but solid-state relays are becoming more popular for their increased performance and reduced environmental footprint. Recent experience has indicated that interruption of current with an inductive load can damage solid state relays by momentarily exceeding their voltage rating. This has been observed by some CP technicians when they return to site to check on a previously installed interrupter, only to find it overheated and not interrupting. This study will examine the various sources of inductance in impressed current CP systems and discuss methods for mitigating the inductive effects during interruption. To demonstrate the effectiveness of these methods, an electrical circuit was created to mimic a cathodic protection circuit, and the effectiveness during interruption was measured using an oscilloscope.  

Product Number: 51320-14621-SG
Author: Michael M. Dockery, Stephen B. Gibson
Publication Date: 2020
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