灌区水费征收的历史与启示

建立科学合理的水利价格收费管理体系，是水利部1993年提出的水利“五大体系”建设的重要内容之一。我国灌区很早就有征收水费的历史，可为现行的水费改革提供经验与启示。目前水费已进入计收阶段，两者本质区别在于征收是一种政府行为，而计收是一种市场行为。现代水费突出供水的商品性，是供水价值的完整体现，而古代水费未考虑供水成本，是供水价值的不完整体现。灌区水费的历史表明：水费产生与发展与社会经济发展水平息息相关，水费必须适宜社会经济发展的需要，同时水费能促进社会经济的发展，现在我国正进行社会主义市经济的改革，水费也必须适宜改革的要求，向更真实的反映水利工程供水价值的方向改变。

Design capabilites and structural characteristics of generating units of the Three Gorges power station

At present, the 14 hydroturbine generator units of the left power station of the Three Gorges project are being manufactured or installed. The difficulties in design and manufacture of the hydroturbines consist in great water head variation, high guaranteed value of the optimum efficiency, high stability requirements in the high head operation zone, lower pressure fluctuation index for the draft tube, large size of the turbine components, and other requirements for taking account of the turbine components' abrasion by sediment, material selection, and transportation of the large-sized components, etc. The difficulties in design and manufacture of the electric generators consist in strict requirement for their performace parameters needed by electric networks, great thrust bearing load, complicated structures of the water cooled stator winding, the stator frame and the rotor spider, etc. Through technical consultation, getting in close touch with the designers and manufacturers, strengthening the supervision of the manufacture of components, and with the help of the successful manufacture experience on other largesized generating units and new technical results, some feasible solutions to many of the above-mentioned difficult problems have been found.