High Voltage Subsea Pump – A Low Cost Subsea Boosting Enabler

Abstract

In a cost constrained scenario, technology driven solutions aiming at CAPEX reductions are crucial to make Subsea Processing (SSP) projects economically attractive. Subsea Processing encompasses three main fields: (i) Subsea Gas or Liquid Separation, (ii) Subsea Compression and (iii) Subsea Boosting - Multiphase or Water. Despite the fact that Boosting is a SSP discipline in itself, both Separation and Compression will also rely on subsea pumps to support the process. Although subsea boosting technology is available and has been successfully deployed in several projects, high cost of system infrastructure is still a barrier for a broader technology adoption. Typically, a high boost subsea pumping system will require both topside and subsea infrastructure. Topsides, at the floating production unit, a subsea pump will require electric power, a variable frequency drive (VFD) to control motor speed, and a hydraulic power unit (HPU) to supply subsea barrier fluid to the motor (except for ESPs). Subsea, a pump module, power connections and a high voltage umbilical are necessary pieces of equipment without which the pump cannot be powered or installed. Aiming to reduce subsea umbilical cross-section and consequently overall system cost, operators have collaborated to develop a high(er) voltage subsea motor. Currently, existing subsea motors are powered with voltages ranging from 4.16 kV to 6.6 kV. For umbilical power dissipation, higher voltage yields a square-law reduction effect. Since ampacity (amount of electric current a conductor can carry) is a function of to the amount of copper, lower amps translate into less copper. The program scope comprises the design, components qualification and prototype build of a permanent magnet subsea motor to operate at 13.6 kV. Beta prototype design and ratings were based on a existing 3.2 MW Permanent Magnet Motor (PMM).