Technical Article

What Are Solid-State Decouplers and How Are They Used?

Solid-state decouplers are widely used in the energy industry. But many people don’t understand what they are, how they function and the many ways in which they can be used. This article will arm you with a basic understanding of them – in layman’s terms.

A decoupler simultaneously performs two electrical functions: DC isolation and AC grounding. This seems like a conundrum: how can something be electrically isolated and safely grounded at the same time? The easiest way to understand how a decoupler works is via an example of its most common use: a buried pipeline.

It can be helpful to think of a decoupler as a filter, which handles four different scenarios:

Cathodic Protection: Cathodic Protection (CP) systems are often necessary to prevent galvanic corrosion of a pipeline or other metallic structure. A CP system provides corrosion protection by applying a low voltage negative DC bias to the structure.  However, required safety grounding systems connected to the structure short this CP current to ground and can compromise the efficiency of the CP system. Under normal circumstances, the decoupler functions to isolate or block the flow of DC current (cathodic protection) to other equipment or grounding material, thereby eliminating any negative influence on your CP system caused by neighboring equipment or grounding materials. Yet the decoupler also provides safety grounding protection from AC faults and lightning.

AC fault protection: AC fault current generated by a failure of nearby equipment is a safety hazard. This AC current can be transmitted via the pipeline, endangering nearby workers or causing damage to your pipeline. When an AC fault occurs, the decoupler instantly conducts fault current to ground, carrying AC current away from the pipeline and providing instant protection.

Lightning protection: When a lightning strike occurs, it can present a safety hazard to personnel and pose a risk to the pipeline. The decoupler behaves in the same way as it does during an AC fault. It safely channels the high-voltage DC current of the lightning to ground, protecting nearby workers. As soon as this event has ended, the decoupler automatically switches back to its DC isolation/cathodic protection role.

Mitigation of induced AC current: Many pipelines are buried along a shared right-of-way with high-voltage power lines, which induce AC current in the pipeline. This is not only a safety hazard to workers, but can also cause corrosion issues. Decouplers such as the PCR or SSD are designed to continuously conduct induced AC current to ground, mitigating this risk while simultaneously isolating your CP system.

Visualizing How Decouplers Work

AC Mitigation

Using an AC mitigation application as an example, the diagram above visually summarizes how the decoupler functions.

In AC mitigation applications, a zinc or copper mitigation wire is laid next to the buried pipeline and is electrically connected to it. The job of the mitigation wire is to safely channel induced AC to ground. But this creates a challenge for cathodic protection: Because the mitigation wire is electrically connected to the pipeline, the cathodic protection system must now protect both the pipeline and the wire, which requires significantly more CP current and may result in inadequate cathodic protection of the pipeline.

Installing decouplers between the pipeline and the mitigation wire, as shown, isolates the two during normal operation to ensure proper cathodic protection, while simultaneously providing safety grounding and mitigation of induced AC.

Other Electrical Applications

In addition to buried pipelines, decouplers are used to provide similar protection in numerous other applications, including:

To learn more about these applications, please click on the links above. For a more detailed introduction to decouplers, please view our Decoupler 101 video series.

Questions?

Please contact Dairyland using our contact us form or at (608) 877-9900 with any questions about solid-state decouplers, cathodic protection or over-voltage protection.

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