Long Cable Applications with PM Motors and MV Drives

Subsea Pump applications commonly use induction motors due to their rugged design and simple construction. However, such motors operate at low power factor and efficiency. These issues are minimized with Permanent Magnet Motors (PMMs) that operate at higher power factor and lower currents. Lower stator current is desirable because losses are an important factor with long umbilical cables between drive and motor. A PMM also allows an increased rotor gap reducing hydrodynamic drag on the motor and enabling higher shaft speeds. In this paper, operation of a mud line pump (MLP) coupled to a medium voltage PMM that is powered by a medium voltage (MV) drive over a 10.5 km cable length is presented. Motor starting and operation under load disturbances are investigated to show drive and motor performance. Waveforms showing steady state operation are presented to show benefits of the MV drive. The overall benefits of a PMM as compared with an induction motor based on operating experience are included.