The turbine efficiency curve calculation is based on rated head design gross

The turbine efficiency curve calculation is based on

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residual flow, the load (in case of isolated grid), the gross head and the efficiencies/losses. The turbine efficiency curve calculation is based on rated head (design gross head less maximum hydraulic losses), runner diameter (calculated), turbine specific speed (calculated for reaction turbines) and the turbine manufacture/design coefficient.
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RETScreen Inputs ....... The RETScreen-Small Hydro Project Software is written in Visual Basic Code and provides a means to calculate the available energy at a potential small hydro site that could be provided to a central-grid or for isolated loads In RETScreen, hydrological data are required to be specified as a flow duration curve, which represents the flow conditions in the river being studied over a period of time. How do we read a Flow Duration Curve … If we look at the flow value at ‘60% exceedence’ we will see that it is 1.3 m 3 /s. This does not mean that the flow rate is 1.3 m 3 /s for 60% of the time, but that the flow is equalled or exceeded for 60% of the time , so basically the flow is at this flow or at a higher flow for 60% of the time. If we look at the flow at 20% exceedence it is 3 m 3 /s; this is a higher flow rate, so the flow is only at or greater than this flow rate for a smaller proportion of the year. If you look at 100% exceedence, it is 0.25 m 3 /s, which is the lowest flow rate recorded, so by definition the flow in the river is at this flow rate or more for 100% of the time. It does not necessarily mean that the flow rate is 0 for 100% of time.
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Flow rates between Q0 and Q10 are considered high flow rates, and Q0 to Q1 would be extreme flood events. It is important that hydropower systems are designed to cope with such extreme flows. Flows from Q10 to Q70 would be the ‘medium’ range of flows and you would want your hydropower system to operate efficiently right across these flow rates. Flow rates from Q70 to Q100 are the ‘low flows’ when hydropower systems will just be operating but at a low power output, and as you move further to the right on the FDC hydro systems will begin to shut down due to low flow. As flow rates move from Q95 towards Q100 you move into the low-flow draught flows. From historical records of water flow, a Flow Duration Curve (FDC) can be built. The flow duration curve is a plot that shows the percentage of time that the water flow in a river is likely to equal or exceed a specified value of interest (the area below the curve is a measure of the potential energy of the river or stream). For instance, the FDC can be used to assess the expected availability of water flow over time and the power and energy at a site and to decide on the “design flow” in order to select the turbine. Decisions can also be made on how large a generating unit should be. If a system is to be independent of any other energy or utility backup, the design flow should be the flow that is available 70% of the time or more. Therefore, a stand- alone system such as a mini hydro plant should be designed according to the flow available throughout the year; this is usually the flow during the dry season. It is possible that some streams could dry up completely at that time.
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Figure 3 shows the FDC for the time series under study. From this figure it is possible to observe that for nearly 80% of the time the water flow is equal or below to 28.4 x 10 5 m 3 . Also, it shows
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  • Spring '20
  • Design Flow, Cross flow, Natural River Flow, Hydro Project Software

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