DAC February 2022

Drives & Controls & BACK TO BASICS n SPONSORED BY Tapping into flowing water to generate power Flowing water represents a huge opportunity for small-scale generation of clean energy with rapid paybacks. According to ABB’s UK water industry manager, Clayton Mead, such applications are easier and cheaper than you might think, and VSDs can play a key role. I n 2018, the UK generated an estimated 1.87GW of power from hydroelectricity – equivalent to 21% of all electricity generated from renewable sources that year. Hydroelectric schemes can range in size from large power plants, down to micro-generation and run-of-river installations. In Scotland, where I live, there is a huge untapped potential in the form of the many reservoirs, dams and watercourses across the country. Huge volumes of flowing water could be harnessed to create green electricity from existing natural and man-made processes. While every project may have its own technical challenges, many hydroelectric installations are, in fact, surprisingly straightforward and low-cost. All you need is gravity, a turbine and a regenerative variable-speed drive (VSD). As long as there is a flow of water, almost any watercourse can be harnessed to produce hydro power. However, with that said, from an electrical engineer’s perspective there are some technical aspects to consider in any such installation. The process is simple: the force of flowing water turns a turbine-generator, and the electrical energy created feeds into the VSD. The use of a regenerative drive allows power to flow from the turbine to the grid, unlike a conventional VSD. It uses an active rectifier, which has the added benefit of producing extremely low harmonic content. The VSD is essential to the process, because attempting to connect a turbine to the grid without one would result in power quality issues. A regenerative VSD can also manage any temporary loss of connection to the grid, using braking resistors. Many hydro projects are in remote locations with poor grid stability. If the grid connection fails, the electrical energy still has to go somewhere, without risking damage to the hydraulic and mechanical equipment. The braking resistor turns the excess electricity into heat, and because it can be included as an built-in feature of the regenerative drive, no additional equipment is needed, which can reduce the need for maintenance – especially important in remote or unmanned facilities. n