Getting Started Resource
When Do I Need a Dairyland Decoupler?
The short answer is that a decoupler can be used for a variety of purposes and applications, anytime it is desirable to isolate DC current (CP current) while simultaneously grounding AC fault current and lightning current. This could be to separate your cathodically protected structure from a grounding system, or from other structures.
Let us explain further. In the oil and gas business, metallic structures including such things as pipelines and tanks, are made more corrosion resistant by the application of cathodic protection current. Typically, devices such as a rectifier are used to provide this current to the pipe, which shifts the potential of the pipe more negative vs. other structures, preventing corrosion.
Corrosion industry professionals also have a responsibility to protect personnel from the dangers of over-voltage conditions, such as lightning or AC fault events. In order to accomplish this a method of safety grounding is required.
Unfortunately, the two goals stand in opposition to each other. Grounding systems interfere with the cathodic protection on the pipe, providing a path for CP current to be diverted to the grounding system, or to other structures electrically connected to them. Often times, this effect makes it difficult to obtain the proper levels of cathodic protection current necessary for corrosion prevention.
And this is where the decoupler comes in… a solid-state device that allows safety grounding of a structure such as a pipeline, without interfering with CP current that was placed on it for corrosion prevention. This process is commonly referred to as “decoupling.” Decoupling can be defined as: utilizing a device that blocks direct current while providing continuity for safety grounding.
DC Decouplers are commonly used for applications such as:
- Isolating electric equipment from grounding systems, while still meeting electrical codes for safety
- Insulated joint over-voltage protection
- Connecting a cathodically protected pipeline to an AC mitigation system
- Tying a cathodically protected pipeline to a gradient control mat
- Grounding of power cable sheaths/casings to substation grounding systems
- Separating a facility with CP from power utility grounding systems beyond the transformer