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Experimentation was performed to determine if there might be a way to further reduce the AC voltages on pipelines better than the existing system of just using parallel ground paths as a mitigation technique.
Pipelines located near high voltage alternating current (AC) transmission lines may be subjected to induced AC current buildup. Present mitigation strategies employ parallel electrical paths, effectively dumping excess electrical charge safely to ground. These strategies use capacitors to stop direct current flow down these parallel paths which maintains the integrity of cathodic protection systems installed on the pipeline while allowing induced AC currents to freely take the parallel path to ground. Experimentation was performed to determine if there might be a way to further reduce the AC voltages on pipelines better than the existing system of just using parallel ground paths as a mitigation technique. Transformers can be added to the grounding path design to create a resonant condition, referred to as a RLC circuit consisting of a resistor (R), inductor (L), and capacitor (C), from the known frequency of the induced AC which will remove energy from the circuit in the form of a magnetic field or electric field. When a RLC circuit is tuned to its resonant condition the power angle is zero, thus removing unnecessary impedance due to capacitance only, which is the case for current AC mitigation designs. Additionally, a transformer can be designed to transfer energy to the secondary effectively helping drain energy which reduces the induced voltage on the AC mitigated pipeline and the total energy returning to ground.
Key Words: AC Mitigation, Mitigation, RLC Circuit, Energy Transformation.
This paper involved a case study of a project involving AC interference on pipelines located in Canada where soil resistivities increase rapidly by up to several orders of magnitude once water in the soil freezes in the winter.
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Three recent international pipeline projects illustrate that the typical surface profile height and abrasive blast cleaning requirements in today’s coating standards and specifications have not been sufficient to define the adequate level of the abrasive blasting.
An AC interference study in advance of an upgrade of a transmission line. Field measurements on the pipelines were compared to computer modeling results and known operating loads to validate a baseline model.