By Ritesh Gupta

Wind farm SCADA systems are predominantly provided by wind turbine original equipment manufacturers (OEMs). Other than the core visibility and control functionality aspects, these systems provide reporting facilities and, where available- an interface to the wind farm control system- where real and reactive power control are available.

The OEM system typically provides a real-time interface, currently most likely to be OPC, to allow third party systems access to the current values and also to commands. They also offer an interface to historical data, which is typically stored in a SQL relational database.

There is a move towards providing standard interfaces to the OEM SCADA systems, using the IEC 61400-25 standard, but this is not yet universally available, says Alok Kumar, Head of Group, Independent Engineering GL Garrad Hassan.

Change of focus

Kumar says the focus of owners and operators of wind farms has shifted from individual wind farms to their portfolios. Owner operators with more than a few wind farms require a portfolio management system to view the current status of their wind farms from a central control centre and to be able to efficiently report across their portfolio.

“This shift of focus to the portfolio has resulted in a number of third party portfolio management systems becoming available and also for some larger owner operators to develop in-house portfolio solutions or to integrate their renewable assets into existing systems,” says Kumar.

For its part, GL Garrad Hassan offers WindHelm Portfolio Manager, a single platform for the monitoring, optimisation and control of any grouping of operational turbines, farms and portfolios. It offers consistent access to, and breakdown of, SCADA data. One of the major features is operational reports to facilitate optimisation including power curves, availability, meteorological data etc.

Reporting

Efficient reporting and reporting by exception allow asset managers to be able to review more wind farms, increase their reporting frequency and respond more quickly to potential issues. Performance losses due to reduced availability and reduced efficiency can be caught more quickly and remedied, hence avoiding lost production.

The datasets across fleets of wind turbines allow the statistical data from the wind farm SCADA systems to be used for condition monitoring purposes, allowing identification of major component issues many weeks in advance of failure, allowing repairs to be scheduled before there is lost production and before failure takes place, says Kumar.

Structural analysis software

Kumar explains that offshore wind structures are typically designed using a combination of Beam-element and Finite-element structural analysis software.

Finite-element software is required to model more complex areas of the structure such as transition pieces, challenging jacket joints and concrete gravity based structures.

“Calculating the loads for a WTG foundation structure is significantly more complex, than with a traditional offshore structure, due to the large time varying component of the loads. This means analysis of time-series loads and resulting fatigue loading is of paramount importance,” says Kumar.

The team at GL Garrad Hassan has also developed Bladed Software, which can generate time-history loads from a WTG and calculate the load time-history at any point within the offshore wind foundation. Bladed offers a Windows-based interface and supports calculations of combined wind and wave loading, with full aeroelastic and hydroelastic modeling.

Structural Design Process

Typically the structural design process can proceed in two ways:

• Coupled analysis: wind load time-histories are generated in WTG design software (such as Bladed) and imported into proprietary structural design software which calculates the wave and current loading independently (hence coupled).

The combined stress-histories from the wind and wave loads are then calculated throughout the structure and members/ joints are checked using a suitable offshore design standard. This is the method traditionally used in the offshore wind industry and is conducted in an iterative design loop with the foundation designer and WTG designer.

• Integrated analysis: this method calculates both the wind and wave/ current loading in the WTG design software and generates load time-histories at every point in the structure. Proprietary structural design software is then used to undertake the design code checks. This method is considered to offer more efficient designs and hence cost savings to the client. The method is now becoming more widely accepted in the industry as cost reduction becomes critical, says Kumar.

In terms of selecting the most suitable foundation type for the site (both technically and economically) this depends on a number of key factors, primarily; the water depth, geotechnical conditions, local extreme load cases, the WTG design (e.g. frequency window, tower top mass), local costs and availability of suitable installation equipment.

Historical data, such as that gathered around maintenance flare-ups or downtime averages, will also form trends for certain turbines within certain foundations and conditions. This will ultimately help software developers make more proactive software solutions that help in real-time situations and in the pre-planning stages of any new wind farm. Standardising interfaces to the OEM SCADA systems will also help shape how farm operators run their assets more efficiently, which is good for all parties involved. When this will happen is not known, but is a much awaited service.