Some Practical Strategies and Methods for Large-Scale Hydropower System Operations in China Chuntian Cheng 1; Jianjian Shen1; Xinyu Wu1; Gang Li 1; Shengli Liao1; Kwok-wing Chau2 1Institute of Hydropower and Hydroinformatics, Dalian University of Technology, Dalian 116024 China. E-mail: ctcheng@dlut.edu.cn 2Department of Civil & Structural Engineering, Hong Kong Polytechnic University, Hong Kong, China. E-mail: cekwchau@polyu.edu.hk ABSTRACT With the rapid increase of number and capacity of hydropower plants operated by single dispatching departments in China, more attention should focus on seeking for more robust methods with reducing dimension curse, improving effectiveness and practicability of optimization results and enhancing computational efficiency of large-scale complex hydropower system operations. In this paper, a general solution framework for large-scale complex hydropower system operations is presented from the real hydropower systems in China. The framework consists of intelligent strategies to reduce problem size during modeling, integrated optimization methods and search methods to vanquish dimensionality difficulties effectively and cope with complicated spatial-temporal constraints, as well as interactive interfaces to adjust optimal results. Two case studies are given out. Keywords: Large-scale; Hydropower operation; Optimization; Dimensionality reduction; Integrated method Introduction Over the last two decades, China’s hydropower has undergone rapid development. Up to the end of 2011, the installed capacity of hydropower has reached 230.51 GW. More than 45,000 hydropower plants have been in operation, including about 400 ones with more than 50 MW generation capacity, 85 ones with more than 300 MW, as well as 32 ones with more than 1000 MW (Huang and Zheng 2009; Cheng et al. 2011a). The majority of hydropower plants are concentrated in southwestern regions and operated by a few large-scale regional and provincial power grids in an integrated fashion. For instance, China Southern Power Grid (CSG), whose total hydropower installed capacity amounts to 50 GW, is in charge of more than 100 large and medium-sized hydropower plants with more than 350 hydropower generator units. According to the “Twelve ‘Five-Year’ Plan” released in 2011, China will continue to exploit the abundant hydropower resources in southwestern regions to meet rapidly growing demand. The focus will be primarily on the development of 6 hydropower bases, i.e., Jinshajiang River, Yalongjiang River, Daduhe River, Lancangjiang River, Nujiang River and the upper main stream of Yellow River. Up to the end of 2015, some of these large cascaded hydropower systems will be completed and implemented into operation successively. It is projected that, in that time, the scale of hydropower installed capacity in a single regional power grid or provincial power grid will be more dramatic. As an example, the hydropower installed capacity in Yunnan Power Gird will reach 75 GW in 2015, occupying about 73.4% of provincial total generation capacity. With the rapid expansion of hydropower systems, long distance and large scale electric power transmission is necessary for effective utilization of hydropower resources. Thus more complex spatial and temporal constraints are imposed on the operation and management of hydropower systems. There are traditional hydraulic and electricity connections amongst plants and cascaded systems, but also new electric transmission constraints amongst power grids. The operation of hydropower systems exhibits remarkable large- scale and nonlinear characteristics. It faces great difficulties and challenges to formulate and solve the optimization problems. Hydropower system is generally known as one of the most complicated application systems in the field of water resources (EL-Hawary and Christensen 1979; Yeh 1985; Simonovic 1992; Laud and