Innovation in Global Power - Parsons Brinckerhoff

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Hydropower – New Technologies, New Considerations access way into the turbine pit, with an unsymmetrical load distribution. The integral design of the generator support bracket foundation with the turbine pit wall was complex and fraught with constructability issues to ensure that the machine alignment during a worst case operating scenario would not exceed generator design tolerances. The alternative of supporting the generator thrust bearing directly off the pump-turbine head cover would have negatively impacted on the access to the pump-turbine for routine maintenance and deemed no overall reduction in the total unit outage for major pump-turbine overhauls. A partial compromise was reached by ensuring there was enough height in the turbine pit to temporarily lift and suspend the headcover to work on the turbine. • Pump starting system. The client specified originally a dual static frequency converter system (SFC). These devices act like a variable speed drive to start the unit in pumping mode. In conducting a reliability cost benefit study for the forecasted pump duty, we verified that a single SFC system with 50 percent redundancy resulted in considerably lower plant and powerhouse construction costs. Pre-Feasibility Design for Asia Project. This project, which is for an independent power producer (IPP) and is confidential, is a 300 MW two-unit pumped storage scheme. We recently completed the pre-feasibility conceptual design stage, for which we developed two interesting solutions: • Ring dyke embankment. We located a suitable location for the lower reservoir, which fit in well with other desirable features at the selected location. There was no natural depression for the upper reservoir, however, particularly at a high enough elevation to offer an attractive economic solution. We investigated placing a ring dyke embankment on top of the hill to create the upper reservoir. This option gave a more attractive ratio of head to horizontal distance between reservoirs, a key survey requirement for identifying potentially economic reservoir locations. • Deep silo powerhouse. Instead of the conventional underground scheme, we proposed a deep silo powerhouse approximately 130 m (427 feet) deep (Figure 1). Silo powerhouses have been used on other projects, but we could not find any example of one as deep as this one. The silo powerhouse eliminates many of the tunnels required for an underground powerhouse such as those for vehicle access and ventilation, and hence was intuitively cheaper when considering the local topography.This concept was adopted for the purposes of costing the scheme in parallel with a market and economic study to verify in principle that there was a potential commercially viable project. Both of these solutions will be tested at the feasibility stage when geological drilling is performed to better understand the site conditions and an alternative underground scheme will be studied and priced to verify the better option. http://www.pbworld.com/news_events/publications/network/ The Future of Pumped Storage The advances mentioned above and others in pumped storage technology, plus the fact that underground schemes are often desirable because they minimise visual impacts, will continue to make pumped storage an important part of power generation schemes in the future. For example, a scheme with the sea as the lower reservoir (i.e., pumping sea water) is in operation in Japan. This type of scheme may be suitable in other locations around the world. In addition, variable speed generators have been installed in some pumped storage plants to obtain the best turbine efficiency in generating and pumping modes. Traditional large pump storage will benefit from the renewed interest in nuclear power generation expansion, as such plants operate at a constant load and need to be complemented with other more dynamic and flexible generators to suit the varying power system load demand. Finally, pumped storage will play a key role also in “alternative” power generation schemes. For example: • Pumped storage has significant advantages in networks with a high proportion of wind power. • Disused deep open cast and underground mines could be adapted for pump storage. • There are benefits to be gained from combining tidal generation with pumped storage to optimise power delivery when the tidal pattern is out of phase with the power demand. Acknowledgements. The authors wish to thank Mr. F. Louwinger of Eskom Holdings Ltd for his consent to the publication of this article and for his useful comments. Ian McClymont is an electrical engineer with more than 30 years experience on hydro-electric power development and refurbishment projects. He has considerable experience with pre-feasibility and tender designs of pumped storage schemes. Paul Reilly, a mechanical engineer, heads the hydro group in Christchurch, which provides a range of services including new development design, refurbishment/ enhancement, owner’s engineer, and due diligence. He has worked for more than 14 years on numerous international and New Zealand hydro projects. Figure 1: Conceptual design of a deep silo powerhouse. PB Network #68 / August 2008 24
http://www.pbworld.com/news_events/publications/network/ Hydropower – New Technologies, New Considerations Planning for Mini Hydro in Distributed Generation By Tony Mulholland, Christchurch, New Zealand, 64 3 963 1514, mulhollandT@pbworld.com ©PHOTOGRAPHER: TONY MULHOLLAND Mini hydro generation is on the rise around the world for two primary reasons— recover energy and meet growing demands for distributed generation. Tapping into his expertise in hydro scheme development, the author outlines some primary considerations for planning and developing a mini-hydro facility, which is defined broadly as 100 kW to 10 MW. Figure 1: A 3 MW mini hydro station connected to an existing dam outlet works. We in the Christchurch office have seen a renewed interest in small hydro by owners seeking to increase revenue by recovering potential or kinetic energy in waterways from existing and new plant (Figure 1). Typical applications include: • Energy recovery from water storage and water supply pipeline outlets • Replacement of inline pressure reducing valves (as found in industrial process plant and municipal water distribution pipework) • Environmental release turbines at water storage dams • Irrigation canal outlet structures and drop structures • Lock gates • Even old watermills. Small hydro is also key to distributed generation, which is seen as increasingly important in future power generation. Financial incentives are available in many countries to supply green energy, which can significantly increase the value of hydro energy sales. The author has experience of schemes in Australia and UK that achieve almost double the value for their energy when compared to energy from fossil fuels. When considering a mini hydro facility, a large range of options and engineering factors need to be taken into account. The following discussion is based on our extensive experience in hydro scheme development—starting in the pre feasibility stage and continuing through design, construction, operations and maintenance. Planning for Mini Hydro: Concept Design The usual approach to planning a mini hydro is to begin with a pre-feasibility study to: • Evaluate the energy resource that can be recovered (in MWh) • Find out critical information about the site, such as the head and flow durations, transmission connection point, and voltage. • Establish the number of generating units and unit capacity (kW or MW). Normally the first estimate of the number of units and capacity is obtained by selecting the arrangement that provides the maximum net present value (NPV). This is done by evaluating the financial value of the energy recovered and the corresponding capital costs for various sizes of generating plant. Depending on turbine type and site flow duration, a further complexity to this process is that more units may provide a better efficiency over the flow range. From information gained in the pre-feasibility study, a preferred concept design can be prepared. This design will later form the basis for the specifications/detail design for tendering. In the distributed generation case, the mini hydro will generally be connected to a local power network. A connection usually requires permission from the network owner, who will be particularly interested in the type and size of generator being selected, and will have a list of requirements for connection, such as protection requirements. Early in the study the engineer should clarify with the network owner that the generator can be connected to the network and discuss what, if any, modifications are required of the existing transmission network. Sites that are remote from an existing network may make the scheme not viable because of the level of investment required in transmission infrastructure. Developers and owners generally prefer induction generators for mini hydro because they are cheaper and simpler than synchronous generators. Induction generations do have a 25 PB Network #68 / August 2008
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Innovation in Global Power - Parsons Brinckerhoff

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