AC interference between co-located pipelines and high voltage AC powerlines can result in safety hazards to operating personnel and the public under powerline steady-state and fault conditions.
Under steady-state conditions, AC voltages are induced on the pipeline via electromagnetic coupling. Under fault conditions, high AC voltages can be present via electromagnetic coupling and AC currents discharging into the earth from the powerline structures, i.e., conductive coupling. These high voltages can result in serious injury or death to any person in contact with any above-ground metallic appurtenance that is electrically continuous with the pipe.
The type and magnitude of AC interference hazards are dependent on many factors including the co-location configuration, the electrical resistivity of the soil, the AC currents on the powerline, and the powerline and pipeline characteristics. Consequently, AC mitigation strategies must be put in place to ensure the safety of all persons and must be tailored according to the various conditions.
This paper discusses the factors that should be considered when designing AC mitigation systems for pipeline facilities. Such factors include facility layout, isolation points, fencing, and ground conditions. The paper also discusses the different mitigation strategies that can be implemented including gradient control grids, ensuring electrical continuity, and grounding.
When a pipeline is co-located with an AC powerline, it is subject to AC interference effects. These AC interference effects can result in safety hazards to operating personnel and the public under powerline steady-state (normal operation) and fault (short-circuit) conditions.
The possible AC hazards under fault conditions include electrical shock to personnel and the public resulting in serious injury, damage to the pipe coating and pipe wall, and damage to pipeline systems and components (e.g., cathodic protection rectifiers, sensing devices, gaskets, and valve motors).
The mechanism of interference and the type and magnitude of hazards depend on many factors including the co-location geospatial configuration, the electrical resistivity of the soil, the AC currents on the powerline, the duration of the hazard (fault clearing time), and the powerline and pipeline characteristics.
To ensure the safety of all persons contacting the pipeline and to maintain integrity of related systems, a mitigation strategy must be developed and implemented. Mitigation of AC hazards may also be required for compliance depending on the jurisdiction.
