STRAY CURRENT CONTROL BY A NEW APPROACH BASED ON TRUE POTENTIAL MONITORING

摘要

In presence of stray current interference due to DC transit systems, CP is operated at so-called “constant potential” condition. This technique consists of a continuous measurement of the pipeline potential by a fixed reference electrode, and the use of such measured potential to pilot the feeder dynamically, in order to maintain that potential constant. An accurate analysis of this technique reveals that what is maintained constant is IR drop in soil rather than the true potential of the structure. On the basis of this evidence, a new approach was investigated, consisting on two steps: the first was the measurement of the true potential by means of a corrosion coupon with an embedded reference electrode, to check protection conditions, and the second was the measurement of the coupon current. The innovation consists of the use of such current to pilot the feeder on the basis of an effective range of the current the coupon should receive. Laboratory tests confirmed the feasibility of such new approach. Modeling and test results are presented and discussed.