5.6 Powerhouse and Switchyard
5.6.1 The type of powerhouse shall be selected after techno-economic comparison of the project layout，topographical and geological conditions，variation amplitude of upstream and downstream water levels，etc.
5.6.2 The layout of the site of a ground powerhouse shall comply with the following principles:
1 The layout of the powerhouse site shall be coordinated with that of other project structures.
2 The layout of power house，auxiliary rooms，main transformer yard，high voltage outlet lines，switchyard，entrance access，diversion structures for power generation and tailrace structures shall be coordinated with each other.
3 For the drainage system on the powerhouse site，dedicated drainage pumps shall be installed if gravity drainage is impractical.
4 For a powerhouse at a hillside，necessary facilities shall be installed on the slopes to prevent mountain flood and rolling stones.
5 The locations of switchyard and main transformer yard should be close to the powerhouse.If limited by topographical conditions，the main transformer and the switchyard may be laid out separately.
6 The powerhouse site is built with environmental protection and landscaping measures.
5.6.3 The location of a ground powerhouse shall be designed based on topographical and geological conditions，with consideration of the requirements for general layout of project，type of powerhouse，flood control，ventilation and lighting，and be finalized after comparison of options.If the penstock is an exposed pipe，the powerhouse should be arranged away from the main flushing direction of emergency water flow or with other anti-flushing measures be taken.
The location of powerhouse should be kept away from any gulley pass.If it is impossible to avoid this，the corresponding protection facilities shall be installed.If the powerhouse is located under high and steep slopes，the slope stability shall be analyzed and corresponding safety protection measures shall be taken.
5.6.4 In the layout of the tailrace channel of a hydropower station，the impact of water flow from the discharge structure outlets should be avoided.If limited by conditions，a training wall shall be built between the tailrace channel and the discharge structure outlets.
5.6.5 The types of flood control structures of a ground powerhouse shall be determined according to the variable amplitude of water level.If the variable amplitude of water level is small and the topographical conditions permit，a flood wall or a flood embankment should be built outside the powerhouse；if the variable amplitude of water level is big，the powerhouse may function for water-retaining or be installed with a flood gate.
5.6.6 The height and width of the machine hall shall be finalized according to the requirements for the layout of electromechanical equipment，installation and overhaul of units，lifting of equipment，ventilation and lighting.(https://www.daowen.com)
5.6.7 The spacing of units in the power house shall comply with the following requirements:
1 If horizontal units are adopted，the spacing shall meet the requirement that the generator rotor may be drawn out during installation and overhaul，and the net spacing between units shall not be less than 1.5m.
2 If vertical units are adopted，the spacing should be set according to the diameter of the generator wind cover，the size and plane layout of spiral case and draft tube；the thickness of the division pier between two neighboring concrete spiral cases and between the draft tubes should not be less than 1.0m，ands the spacing should not be less than 2.0m if there are permanent joints.The thickness of the division pier between metal spiral cases should not be less than 1.0m，and the net spacing between the generator wind cover plates should not be less than 1.5m.
3 The length of the side unit section next to the units shall be determined according to the location of erection bay，the elevation difference between the generator floor and the erection bay，and the working range of the crane，etc.
5.6.8 The area of erection bay should be determined in accordance with the requirement for extended overhaul of one unit.The ground elevation of erection bay should be the same as that of the generator.The erection bay should be located at one end of the powerhouse and be of the same width as that of the power house.
5.6.9 Ventilation，lighting and noise-proof facilities shall be installed in the powerhouse；for riverbed powerhouse，damp-proof facilities shall be installed；and for ground powerhouse and auxiliary rooms in frigid regions，heating（heat insulation）facilities shall also be installed.
5.6.10 For areas between the main machine hall and the adjacent structures such as the erection bay and the auxiliary rooms，permanent deformation joints shall be set based on the foundation condition and the layout of powerhouse.Water-stops shall be installed for underwater permanent joints and vertical construction joints that bear water pressure，and water-stops that extended downwards to the foundation rock shall be firmly connected with the foundation rock.
5.6.11 In the calculation of the integral stability and foundation stress of a ground powerhouse，the middle unit section，side unit section and erection bay section shall be respectively regarded as an independent module and the following computations shall be conducted under various loading combinations:
1 Computation of stability against sliding along the foundation plane and vertical normal stress.If there is a weak plane in the foundation of powerhouse，the in-depth anti-slide stability of powerhouse shall also be rechecked.
2 For the powerhouse with high tailrace water level，the stability against floating shall be calculated.
5.6.12 The foundation of a ground powerhouse to be located on a non-rock foundation shall meet the requirements for strength，anti-seepage，drainage and minimizing differential settlement.
5.6.13 Strength calculations shall be conducted for all structural parts of the powerhouse，and the pressure-loaded parts of high bents shall be further examined for their stabilities.For crane girder，powerhouse framework and components for which deformation values need to be controlled，the deformation calculations shall also be conducted.For the parts of substructures that bear water pressure and the parts of upper structures for which crack width need to be controlled when the structures are being used，the crack width shall be calculated；and for the parts that directly bear vibration load，a dynamic calculation shall be conducted as well.
5.6.14 The architectural design of the powerhouse of a hydropower station shall be developed by using advanced technology，be visually pleasing and elegant，user-friendly，and in harmony with other structures of the project.
