The layout and sizing of the hydraulic turbine and corresponding generating units can be calculated using different computation programs, United States Bureau Reclamation (USBR) manual, Corps of Engineers manuals, American Society of Civil Engineers (ASCE) guidelines for powerhouses and the world known manufacturers experiences.The turbine and generator efficiencies for normal design conditions are taken as 90% and 96% for 750 rpm unit, however it varies with turbines running speed, generator type and type of governor. The runner, the turbine pit and housing dimensions and generator dimensions can also be calculated using different computer software.
Factors Affecting Turbine Size
Following are the few factors affecting turbine size and layout:
- Synchronous speed
- Turbine setting
- Runaway speed
Synchronous Speed It is the permissible specific speed of a turbine and calculated ad unit trial speed. For example for a turbine with 12 poles synchronous generator would require a turbine with 750 rpm of synchronous speed.
It is the centerline level of turbine and usually placed above the maximum turbine water level for a given discharge.
The unit runaway speed can be determined by the computation program such as turbonpro etc for example for turbine with 750 rpm of synchronous speed will have 1350 rpm of runaway speed, however, an accurate value is usually guaranteed by the turbine manufacturer.