33 kV Subsea Power Re-configuration Project

Two of the three platforms generated power to supply all three platforms. Marathon Oil proposed to decommission one of the platforms, which operated with three gas turbine generators, and the remaining generating platform, supporting the non-generating platform. The power management system that manages the power flow between all three platforms was complex.

Marathon Oil requested EPS to carry out a number of transient motor starting scenarios to determine whether the existing 33 kV power network would enable a 4.35 MW motor to start on their East Brae platform. The main concern was whether the limited power generation would maintain a voltage within a transient starting voltage dip limitation of no less than 20%.

At the time, Marathon Oil did not have a detailed work scope. EPS assisted in creating a work scope in the form of a project plan, which consisted of a structured, logical plan to help Marathon achieve decommissioning of the Bravo within a certain time period. EPS set and achieved realistic delivery dates for the following activities:

  • Dynamic motor and load model creation
  • Gas turbine generator dynamic model
  • Check and verify the existing power system model (originally constructed some time ago for an arc flash study)
  • Power system Transient stability model
  • Transient motor starting report
  • FEED study report
  • Offshore motor starting measurement recording
  • Determination of worst case events and scenarios
  • A new 33 kV topside ‘T’ connection solution incorporating new 33 kV switchgear to supply a decommissioning load
  • Inter-platform protection schemes and designs
  • Transformer tap setting optimisation (once the Brae Bravo has been removed)
  • Statement of Requirements for 40 MVA transformer energisation studies
  • Transformer energisation studies
  • Worst-case scenario, transformer energisation scenarios and events
  • Platform-neutral earthing schemes and solutions

Load flow, short circuit, and protection analysis with an arc flash study revision followed.

Given the tight deadlines and budget restraints, the level of service Engineering Power Solutions provided was outstanding. The offshore UPS consolidation project was engineered and designed to the platform’s requirements and offshore standards minimising platform shutdowns.

Mr Low – Petrofac Oil&Gas