ABSTRACT

AC interference from high voltage power lines can constitute an electric shock hazard and a threat to equipment integrity during both normal operation conditions and fault conditions. Simplified analysis methods can lead to millions of dollars in excess expenses due directly to overdesign or resulting from the consequences of underdesign. This paper presents a cost- effective AC interference mitigation method, which is made possible by the power of presently existing computer software. The importance of the soil?s multilayer soil structure in determining the performance of mitigation systems is discussed. This mitigation method is compared with other types of mitigation systems.

INTRODUCTION

A pipeline which shares a common corridor with AC transmission lines becomes energized by the magnetic and electric fields surrounding the power system in the air and soil. This AC interference can result in an electrical shock hazard for people touching the pipeline or metallic structures connected to the pipeline... or simply standing nearby; furthermore, damage to the pipeline?s coating, insulating flanges, rectifiers or even direct damage to the pipeline?s wall itself can occur. This paper discusses recent advances made in mitigating electromagnetic interference generated by electric lines on neighboring pipelines (oil, gas, water). It describes state-of-the-art analysis tools and mitigation techniques which effectively reduce AC interference to acceptable levels, while yielding tremendous cost savings compared to alternative methods.

HISTORICAL PERSPECTIVE

In 1976, EPRI and A.G.A. jointly funded a research project which resulted in the development of a hand calculator program to predict inductively induced voltages on pipelines parallel to power lines?.2.3.4.5. Further work was carried out later in a follow-on research program to develop computer software which can handle realistic rights-of-way in which pipelines and power lines are not always paralle16. Subsequent funding by EPRI and AAR focused on interference to railroad facilities?.* and a computer program called CORRIDOR, capable of predicting steady-state induced voltages on pipelines and railroad facilities was made available. In the late 80?s, the ECCAPP (Electromagnetic and Conductive Coupling Analysis from Power lines to Pipelines) was developed to account for both inductive and conductive coupling during fault conditions, a problem which could not be investigated using the CORRIDOR program?...

The preceding work focused mainly on the prediction of interference levels, but very little work was devoted to the development of sound and practical mitigation methods. Indeed, following the initial EPRI/A.G.A.- funded research work, a mitigation method called the Cancellation Wire technique was developed and presented as a highly effective approach to reduce inductive interference. As explained later, it turned out that this method was not appropriate because it transferred dangerous voltages from one location to another. Furthermore, all this work considered the soil to be uniform and did not discuss the effects of soil inhomogeneity on the design of effective mitigation.

Significant work on economically sound and practical mitigation measures started with studies in the Saudi desert

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