DCVG

Off-Potential Interference by Solid State Decoupler

Electrical Circuit for Off-Potential Measurement without SSD Electrical Circuit for Off-Potential Measurement with SSD What Happens while Measuring Off-Potentioal with SSD Connected When CP current (S1) is interrupted: The voltage across decoupler must change by the Icp x Rp voltage drop component that was eliminated A transient current must flow to make this voltage change Until this transient current is dissipated, an Off Potential measurement will not be measured accurately(too electronegative). How to Measure Off-Potential with SSD OFF waveform analysis with a longer than normal On-Off cycle (e.g. 7 On, 3 Off) Determine the time after current interruption where a…
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DC STRAY CURRENT ANALYSIS AND MITIGATION

Introduction DC stray current is defined as current flowing through the path other than the intended. The DC stray current could be either natural sources, e.g. telluric, metallic mineral deposit, or artificial sources, e.g. foreign pipeline, HVDC transmission line, DC tram, etc. DC stray current is a big threat in pipeline integrity. The severity of the risk is a related to the soil resistivity: the lower the soil resistivity, the more likely to form such electrical conductance path, i.e. stray current related corrosion. The root cause of sewer explosion in 1992 Guadalajara Mexico is stray current corrosion of ductile iron pipe….
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AC Corrosion

AC corrosion became a known issue since more and more pipelines are sharing ROW with HVAC transmission lines. It is caused by the metal loss due to AC current leaving the pipeline. There are three different types of AC interference, which are the source of such AC current. Electrostatic Coupling This is also called capacitive interference. It may only happen to well insulated (not grounded) structure, e.g. above ground test station, pipeline near ditch or in stock yard Electromagnetic Coupling This is also called inductive interference. This is the most often seen AC interference mechanism, in which pipeline is acting…
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