Review of Electrical Motor Technologies for ESP Applications

Abstract

AbstractThe electrical submersible pump (ESP) is a key artificial lift enabler within the oil industry. Since their launch in late 1920s, induction motors have been the main motor technology used in ESPs. Recent advancements in technology have opened opportunities for the development of higher performance and more efficient topologies for electrical machines. This paper aims to provide a review of different motor technologies in the well oil and water fluid lifting industry.The analysis in this paper is constructed around a comparison between several electrical machine technologies when exposed to the harsh downhole environment. The dimensions of each machine are similar and provide a fair comparison. The advantages and drawbacks of each motor are presented in respect to key mechanical or electrical considerations. Solutions are recommended when there is evidence from previous work, and several questions are raised for the feasibility of certain topologies in respect to the new challenges.Results show why the induction machine (IM) was selected by ESP providers in late 1920s and why it still has value nearly 100 years later. Permanent magnet machines (PMMs) offer higher power density levels in a smaller package. Synchronous reluctance motors (SyncR) offer a more robust and cheaper alternative, but the design is relatively new and further analysis is still required. Advancements in switched reluctance machines (SRMs) allows for the development of a motor with IM torque capabilities. Both SRM and BLDC (brushless DC) require pulse width modulation (PWM) square-pulse drives, which may prove to be a challenge when driven over a long cable. This paper emphasises the importance of a proper analysis of each motor technology in respect to a particular application. The design of electrical machines should be tailored around the specification of each environment to provide a more robust and efficient system.Although some literature is available on the comparison of PMM and IM in the artificial lift (AL) industry, it seems to promote PMMs with little attempt to suggest improvements for traditional IM topologies, which still offer many benefits in terms of ease of manufacture, robustness and capability to operate in extreme environments such as with high temperatures. This paper discusses several other technologies that have not previously been considered. The aim of the paper is to provide a holistic view of the possible problems each technology will face in the downhole environment and inform future work on possible design improvements for the most promising technologies. In addition, the paper will provide a comparative assessment of the different motor technologies in terms of their strength and weaknesses, and also issues that should be addressed for ESP applications.