FEATURE DRIVES, CONTROLS & MOTORS Keeping the turbine turning
Growing in popularity and commercial viability, renewable energy sources produce more than one-third of the world’s energy. Wind energy alone accounted for 48 gigawatts (GW) generated globally in 2018. Here, Steve Hughes, managing director of renewable power quality expert REO UK, explains how we can keep these turbines turning and ensure that power flows reliably
R
ecent years have seen no shortage of scientific warnings and social movements
to combat the climate crisis. Socially, the past couple of years have seen public protests over climate-related issues reach new levels of notoriety; most recently through the Fridays For Future movement led by the now widely renowned 16-year-old climate activist, Greta Thunberg. Not only do such movements reflect public
sentiment, they also underpin changes on a governmental level. For example, the UK Government has set the goal that 20% of the nation’s energy should be derived from renewable sources by 2020. The country is presently on course to narrowly hit this target, although recent Government analysis indicates that it could be exceeded to reach 50% by 2025. These socio-political movements place
greater pressure on electrical and design engineers involved in renewable energy projects. They must work consistently to maximise the efficiency and efficacy of renewable infrastructure, such as photovoltaic panels and wind turbines. At the moment, wind turbines are most at
home in the UK. The world’s largest offshore windfarm, the Walney Extension, occupies 56-square miles off the shore of Walney Island, off the west coast of England. Another windfarm is to be built in 2020 at Dogger Bank, the large sandbank in the North Sea. Set to begin operation in 2023, the farm is expected to also
Socio-political movements place greater pressure on electrical and design engineers involved in renewable energy projects
house the world’s largest wind turbines. Investments such as these are
positive steps. But, while wind turbines are undoubtedly effective, they are fundamentally limited by their need for real estate. For example, a typical
2-megawatt (MW) turbine installation will generally require roughly 65,340 square feet of space. However, it must also be spaced a certain distance apart to allow for blade-turn and to avoid creating turbulence that disrupts the air flow around other turbines, reducing their efficiency. That’s why there is a need for ever-evolving
However, if we are
designing a variable speed turbine to maximise efficiency, engineers must consider other
power electronics beyond rectification and filtering equipment. This means
designing in measures to ensure that any surplus energy from
REO braking resistor
turbines is dissipated safely without
causing any damage to the VSD. Here, we need an effective braking resistor. In wind generation, these resistors must not
efficiency improvements during the design of wind turbines. In our book, R30: The Past, Present and Future of Power, we anticipate that this growing need for efficient wind generation is set to continue for many years to come.
MAXIMISING EFFICIENCY The key to maximising the efficiency of a wind turbine is for the rotor to capitalise on the aerodynamic power of the wind, which varies frequently. Variable speed wind turbines achieve this by using variable speed drives (VSDs) that adjust the rotor speed. Although variable speed turbines can achieve greater efficiency, they do pose a problem of compatibility as the AC voltage frequency is not constant. This requires effective current rectification, from AC to DC, prior to further conversion at the point where the turbine couples with the grid. All of this can produce erroneous electrical frequencies that may develop into issues, such as harmonic currents, unless properly filtered.
20 OCTOBER 2019 | DESIGN SOLUTIONS
only be able to handle the immediate increase in energy, but also do so consistently after frequent use. In addition, they must balance the capacity for high continuous power with a compact profile, to meet the space-limited requirements of wind turbines. REO UK recently launched the REOHM 155
series braking resistor for this reason. The resistor offers continuous power of up to 3500W, within a compact unit that is rated to IP66 to protect against dust ingress and powerful jets of water. This, we believe, is the prime choice for the wind turbine industry, to help design engineers get the performance they need without compromising on size. The REOHM 155 series is a braking resistor
born of industry experience acquired over decades of work with design and electrical engineers. Because of this, it also happens to be one that’s designed perfectly to meet the mounting pressures on design engineers in these pivotal times for renewable energy. As public outcry inevitably forces more urgent environmental legislative progress from global governments, we can at least ensure that wind generation technology keeps things moving. What else will affect power quality over the
coming decades, and how can engineers prepare? REO UK offers insight in its upcoming ebook. Register for a copy via the website.
REO
www.reo.co.uk
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