Mechanical Integration of Large Two-Pole Variable Speed Electric Motors for High Availability of Liquified Natural Gas Compression Trains: Returns of Experience and Recommendations

Synchronous and asynchronous motor technologies dedicated to high speed make it possible to offer high-power variable-speed compression services without using gearboxes. The mechanical integration of these motors requires special precautions because of the wide speed variation ranges required. The first part of this article explains the mechanical integration rules described in the American Petroleum Institute (API) 541 and 546 standards, which are the most restrictive in the world, and rotating machine signatures of vibrations in case of mechanical looseness. The main linear and nonlinear dynamic mechanisms related to electrical machines are also explained. The second part of the article describes four returns of experience on 15 MW and 20 MW at 3,600 rpm starter-helper variable speed induction motors fed by a voltage source inverter (VSI) and full electric liquified natural gas (LNG) compression trains driven by 75 MW at 3,000 rpm synchronous motors fed by a load commutated inverter (LCI), including the availability and repairability of the rotating exciter-rectifier device. A special focus is made on one return of experience that occurred during on-site commissioning due to vibration instability of a 15-MW two-pole starter-helper induction motor, explaining the mechanism that led to this instability. The last part of this article proposes the recommendations to be followed for synchronous or induction two-pole motors by manufacturer, original equipment manufacturer (OEM), the electronics part catalog (EPC), and user-end in terms of modeling, design, and testing for successful mechanical integration and high availability. See “Nomenclature” for a list of terms and symbols used in this article.