Lightning Protection for Submergible Oilwell Pumps

Lightning protection for electric submergible pumps has long been an area of concern. Related insulation failures are costly and not altogether uncommon. These are due in part to poor-quality grounds and the tightly spaced geometry of submergible motor windings. An improved protection scheme is proposed wherein separate high-and low-current grounds are used, and the rate of voltage rise is limited. These techniques divert the major portion of lightning energy before it reaches the downhole equipment, thus minimizing coil-to-frame voltage stress. It also slows the rate of voltage rise to reduce turn-to-turn stress within a single motor coil. Design considerations are developed for the protection of an electric submergible pumping system, particularly as they relate to the value, quality, and reliability of individual protection components and various grounding systems. Laboratory test data are presented, showing the effects of motor impedance on performance when characteristic lightning transients are applied. Finally, available field data are reviewed.