Returns of Experience and Recommendations of Mechanical Integration of Large 2-Pole Variable Speed Electric Motors aor High Availability of Lng Compression Trains

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 paper explains the mechanical integration rules described in the API 541 and 546 standards which are the most restrictive in the world, and rotating machines signatures of vibrations in case of mechanical looseness. The main linear and non-linear dynamic mechanisms related to electrical machines are also explained. The second part of this paper describes a site return of experience from a vibratory instability of a 15MW 2-pole starter-helper induction motor and explains the mechanism that led to this instability. The third part of this paper proposes the recommendations to be followed for synchronous or induction motor by manufacturer, OEM, EPC and User-End in terms of modelling, design and testing for successful mechanical integration and high availability, and is illustrated by four business cases: 15MW & 20MW @3 600rpm starter-helper variable speed induction motors fed by Voltage Source Inverter, full electric LNG compression trains driven by 75MW@3000rpm synchronous motors fed by Load Commutated Inverter, including the availability and repairability of the rotating exciter-rectifier device.