Over-Voltage Protection: The Critical Differences Between Spark Gaps and DC Decouplers
Isolation joints are essential elements of effective cathodic protection (CP) systems and are used extensively throughout pipeline systems to electrically isolate sections of pipe for a variety of reasons. One of the most common applications is to isolate two sections of pipe from each other to prevent unwanted flow of CP current to adjoining pipe sections which may be grounded or protected by a separate CP system.
Both isolating spark gaps and DC decouplers are commonly used to protect against over-voltage conditions on pipeline isolation joints and storage tanks where cathodic protection systems are applied. Though spark gap devices are often applied because of their relatively low cost, they are not designed for many over-voltage conditions that commonly occur on pipelines. Without fully understanding the limitations of spark gap devices, pipeline operators may unwittingly put their pipeline assets as well as operating personnel at risk from over-voltage events such as AC faults and lightning.
This paper provides an overview of why over-voltage protection on isolation joints is needed, as well as a brief description of the two most common protection technologies – spark gaps and solid-state DC decouplers. The paper offers a detailed explanation of the limitations of spark gaps for use as over-voltage protection devices on pipelines, and explains why properly rated solid-state devices should be used in place of spark gaps for most pipeline applications.
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