Electrification of the Utsira formation : electric system requirements for a power distribution platform

Abstract

The Norwegian oil and energy department instructs operators to look at the possibility for electrification of future offshore installations with power from shore. The offshore installations at the Utsira formation may be suitable for this due to a high power demand and the distance from shore. The objective of this thesis has been to investigate requirements for an electrical power distribution system for these installations. A power distribution platform recieves power from the onshore grid through a HVDC link and distributes it through high-voltage AC cables to the offshore installations. The focus has been on the high-voltage AC part of the distribution system. Requirements and capacities for the following components have been investigated: Voltage source converter Transformers Circuit breakers HVAC Transmission cables In addition the option of integrating an offshore wind power plant in the high-voltage AC distribution system has been evaluated, as well as the modifications required for the mentioned components and the topology of the distribution system. A Simulink model of the distribution system was developed to test the solution for different load conditions. The offshore installations were modelled as a number of 28MWinduction motors with a power factor of 0.9. The voltage source converter was simplified to a constant power source and modelled as two PI controllers for power and voltage. The system currents and voltage levels from the steady state analysis are regarded as good estimates for the future realization of the distribution system with only power from shore. Future steady state analysis of the distribution system should look to the values presented in this thesis in order to verify if their results are within reasonable range. With a wind power plant (WPP) the system components must be able to withstand a higher short circuit current and the circuit breaker ratings must be modified. To avoid this, a current limiter (Is-limiter) could be introduced, which will prohibit the short circuit current contribution from the wind power plant. A new transformer will be required within the distribution system, and the capacity must be equal to the maximum capacity of the wind power plant. If the floating wind turbine technology evolves, a WPP together with power from shore should be capable of supplying offshore installations with power. The fast response and versatile control of the voltage source converter makes it well suitable for balancing the power of the WPP. The balancing would also require a maximum power reserve equal to the WPP capacity in the onshore grid. The offshore installations at Utsira formation is planned to start production in 2016 and will be operational to 2060. These installation could either be run with gas driven turbines located on the platforms or be supplied with power from onshore. Global warming and the world’s demand for gas may call for measures to supply future offshore installations with power from shore. This thesis has shown that there are few technological restraints for the electrification of the Utsira formation with power from shore.