Wind farm reactive power compensation – contributing to grid code requirements

Power systems studies are essential to ensure new wind farms have adequate reactive power compensation, S&C Electric Company tells Engerati.
Published: Mon 21 Aug 2017

With more than 500 GW of wind capacity deployed worldwide, according to the World Wind Energy Association, the importance of wind in the transition to a low-carbon economy is evident.

The engineering challenges of a wind farm development are complex in that they involve transporting and installing large pieces of equipment in locations with often limited access.

But perhaps even greater is the need to ensure the wind farm is compliant with the relevant grid code and that the project has sufficient reactive power compensation.

Wind farm studies

The key here, says Steve Stapleton, S&C’s Consultancy Services Manager for the company’s Europe, Middle East, and Africa regional office is to do detailed studies on wind farms and their connection to the grid and to develop sizing-compensation solutions during the project-conception and design stages to avoid costly delays.

Michail Theodoridis, Power System Engineer at Vestas Celtic Wind Technology, the UK branch of wind giant Vestas, adds that such studies are “super important” in firming up the costs and size for the contract-evaluation and internal reviews. “In some cases, internal resources cannot always accommodate pre-sales (or even post-sales) studies, so the external studies support Vestas fully,” he says.

From Vestas’ perspective, Theodoridis notes, input on such studies is sought as soon as his company’s sales team informs him of the number of turbines and the turbine generator type. This will also indicate the need for equipment such as a distributed static compensator (DSTATCOM) for reactive compensation.

“In our experience, all projects benefit from the additional technical input,” he says.

Wind farms - technical compliance

How the technical compliance of a wind farm is ensured depends on the local distribution or grid code, either of which can vary from country to country and potentially even between different locations within a country. And the needs of each project will be different, says Stapleton.

“In general, there are similarities between wind farms of similar sizes, but in their detail, every wind farm differs – from the turbines used to the connection to the grid and the equipment that is integrated,” he says.

However, there is a core group of characteristics that should be confirmed for any wind project, Stapleton notes.

These include assessment of the steady-state operation, including losses, power flows and voltage to ensure conformity with normal operating and statutory limits.

Other studies include short-circuit analyses to ensure adequate equipment ratings; assessments of flicker, harmonic issues, and other power-quality requirements; and dynamic performance verification.

These typically take about 10 to 12 weeks to complete, depending on the scale of the onshore project. With their greater complexity and scale, offshore wind farm studies could take up to a year.

Such studies can be required at any time during the development, right up to commissioning.  

As an example of their benefit, Stapleton cites a wind farm project that required the retrospective addition of a new harmonic filter to ensure grid code compliance.

“To take out a piece of equipment and reinstall another can amount to as much as 10% to 20% of the total project cost, which can be avoided by doing the correct studies upfront,” he says.

In this case, S&C was able to find a solution that involved modifying an existing capacitor into a harmonic filter at a much-reduced cost.

Reactive power compensation

Another group of studies should focus on the reactive power compensation requirements.

These studies can be done at various stages during the process of developing, constructing, and operating a wind farm, explains Stapleton.

The initial studies will be done with whatever information is available (in terms of the wind turbine type, electrical configuration, etc.) to estimate the reactive compensation requirements, which will provide an overall solution that is compliant with relevant requirements.

From this, elements such as cost, the physical size and layout, and timescales for manufacture will be fed into the wind farm development.

Various iterations of studies may then be done as more data becomes available or the wind farm design changes to look at alternative/optimum solutions. The results of a final ‘as-built’ study will then be provided to the power network utility company to demonstrate compliance.

Wind farm consultancy

Consultancy and project planning are areas where S&C is gaining ground. Regarding wind farms, S&C is primarily known as a supplier of products and services that include DSTATCOMS for reactive power compensation.

From its years of working on global wind farm developments, the company also is now offering this expertise in the form of technical input and design verification on a consultancy basis to parties such as project developers and wind turbine manufacturers.

"S&C is technology-neutral in its approach, and it provides technical expertise independently of whether we are supplying equipment to the project,” says Stapleton.

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