Moray Firth Offshore Windfarm, UK Moray Firth

Project Summary

As part of the Moray Firth Renewables Limited development team which integrates work packages from a number of key consultants, Petrofac is responsible for Work Packages 5 and 6, array electrical layout, and electrical infrastructure and grid connection (OFTO). Petrofac has worked with MORL on the electrical design of this offshore windfarm from concept stage, helping to develop a suitable Rochdale envelope and investigate the impact of design decisions on safety, consents, operation and costs. This was through a three stage iterative approach –  Initialise, Optimise and Finalise, with each stage aiming to evaluate available options and rule out unsuitable ones.The initial scope of work consisted of developing, testing and optimising concept engineering designs for the array electrical layout,electrical infrastructure and export connection.

This specifically included providing engineering input to project cost models and preliminary cost-benefit analysis, supply chain engagement in advance of the main tendering activity and establishing a project engineering baseline for input to Front End Engineering Design (FEED). Petrofac’s original scope has since been extended to include consideration of spare strategies, communication and SCADA protocols and offshore substation structural design and layout.

Key facts

with the development of Petrofac’s offerings for offshore wind, and in particular our acquisition of TNEI, we have a developing presence in the renewables market, and this contract award illustrates the value that offshore oil and gas expertise can bring to this emerging industry

for this and other offshore wind projects, TNEI have developed a software solution that enables the analysis of a large number of array layouts, determining cable lengths, sizes, costs, losses, availability and overall lifecycle costs of each option. This is a semi-automated tool and allows many different layouts and turbine types to be compared quickly and easily to enable concept selection

in this project, Petrofac and TNEI have demonstrated not only their excellent technical capabilities but also an ability to identify and address the key risks and challenges within a wide-ranging and complex project, helping the customer to make robust and sensible design decisions. These were based on an understanding of the electrical, structural, installation and operational issues and the challenging environment in which the equipment and installations will have to operate Long Connections – HVAC or HVDC?

The electrical layout of the Array is closely linked to the optimum export solution, in particular around the number of platforms and capacity of each.  Also, the electrical system cannot be considered in isolation from the supply chain or more critically for offshore, the installation and O&M costs. Considerable attention was given to interfacing with the other work packages throughout the course of this work to manage the uncertainty in available data and ensuring new information is incorporated into the design process in a timely manner.

Given the distance from shore and the capacity of the proposed windfarm, it is deemed beneficial for the project to investigate if a HVAC solution would be sufficient, cost effective and technically feasible or if a HVDC link would be required to avoid restrictions in the power transmission to shore.

There are a number of technical questions relating to the viability of ac export cables over longer distances. These include questions relating to the optimised approach to reactive compensation and the performance/issues of long ac cable systems from both a steady state and transient perspective.

The main technical challenges for this offshore windfarm connection were:

• determining the optimal windfarm capacity and the impact this would have on costs and export connection options
• finding a technically achievable and consentable route for the grid connection
• undertaking detailed electrical studies to consider such things as transient stability and overvoltages, grid code compliance, harmonics, EMF and cable rating calculations
• considering HVDC and HVAC connection options and the technical, commercial and consenting challenges that they each pose