Wind farms have become much more widespread in recent years and they present some new challenges to the electrical systems that they connect to and indeed on the systems that are required to interconnect the units within the wind farm itself. Increasing size is leading to more complex systems and necessarily better MW, MVAr and control requirements. We have the expertise to ensure that electrical power issues are properly addressed and designed to provide wind farms with cost effective electrical systems.
Voltage performance and VAr compensation – depending on the type of generation used and the voltage performance of the system with varying wind regimes – can be critical. The three main types of generation – induction machine, double fed induction machine and fully converted – all have their relative financial and technical merits and drawbacks. Designing a system to cater for them is not a standard process since the connection to the utility, utility requirements, the layout of the wind farm and financial constraints can be very different in every case.
VAr compensation at the grid connection and at points more local to the WTGs has to be assessed. In some cases the selection of the generation type can be included in the compromise required at the design stage, as selection of cheaper generation types can lead to higher costs of system compensation and vice versa. These issues have a bearing on the PV and PQ curves for the plant and the system.
System transients on, and due to, wind farms have to be examined, both to ensure that the wind farm does not impose unacceptable transients on the utility and that disturbances to the grid do not cause unwarranted problems to the wind farm equipment. Controls and protection have to be designed and set accordingly. We have an extensive range of software to assess transients including PSS/e, IPSA, PSCAD/EMTDC, ETAP and EDSA.
Harmonic distortion is a growing issue in wind farms. DFIG systems convert about 10% of a unit’s power and fully converted systems 100%. The use of VAr compensation involves mechanically switched capacitors (which affect harmonic impedance) and fully dynamic compensation generates its own harmonic distortion. Interaction between new connection and existing system distortion is often difficult to assess. We can identify potential problems at the design stage or help troubleshoot existing systems.
The use of DC for connection of large offshore wind farms to the onshore grid system is also being explored at present. This too will have harmonic implications both on the wind farm end of the connection and at the grid connection end. In this field we have major expertise that can be utilised by utilities and wind farm developers alike.
Control and protection issues have to be considered at the design stage and knowledge of system behaviour is a pre-requisite to ensuring that these issues are properly taken into account. Our system analysis experts have an in-depth understanding of these functions in wind farms and utility networks and of how they are best applied to systems.
With our wider wind farm engineering and project development capability we are able to integrate our electrical design and optimisation work with all the other functions. For example, when designing cable systems within wind farms we understand the constraints imposed by environmental considerations and by the road system required for construction and maintenance access. Working with civil and environmental staff is second nature to our design teams.
Our substation experts, system analysis and concept design engineers also have a thorough knowledge of the detailed design and implementation stages of projects. This ensures that the early designs and the analysis are rooted in the practicalities of good engineering practice, facilitating a smooth design process after the concept design stage is complete. Other services include:
- Design and optimisation of wind farm internal electrical systems and connections to utility networks
- Performance modelling of wind farms and associated grid systems
- Assessment and design of connection options and grid modifications for utilities.
Our engineers work closely with our clients to ensure that the best is obtained from both to the benefit of the power system project. We will ensure that power dispatch is a s smooth as possible.
Savings/value added demonstrated
- Optimising the grid connection arrangements can make great savings in capital requirements.
- Life extension studies
Selected project examples
Mott MacDonald has an extensive track record in wind projects in general and in the electrical aspects of them in particular. We have carried out electrical systems work for onshore and offshore wind farms as follows:
- Grid connections work on behalf of utilities such as ScottishPower and National Grid.
- Extensive development and design work for Noble Environmental Power for projects in New England, New York and elsewhere in the USA.
- Grid connection work for developers such as Scottish and Southern Energy, CRE Energy, Amec and British Energy.
- Wind farm internal electrical arrangements for Scottish and Southern Energy, LWP, Nuon/Shell, CRE Energy and ScottishPower.
- Offshore wind farm design for UK projects such as Robin Rigg, Barrow, London Array and Gwynt y Mor.