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Sketch of a medium head PROR plant

Short answer

A PRoR plant has a weir forming pondage, intake, desander, headrace, surge tank, penstock, powerhouse with Francis turbines, tailrace, and switchyard. Pondage stores off-peak inflow for daily peaking; surge tank controls water hammer; Francis turbines suit medium head and large discharge.

Make a sketch to show various components of medium head and relatively large discharge, medium size Pondage Run of River (PRoR) hydropower plant. Also, mention the functions of each component.

A Pondage Run-of-River (PRoR) plant diverts river water through a water conductor like an ROR plant, but stores water in a pondage (daily storage) during off-peak hours so that the plant can run at full output during the peak hours (typically 4–6 hours in the evening). For medium head (about 50–300 m) and relatively large discharge, Francis turbines are used.

Sketch

        River
          |
   ======[Dam/Weir + Gates]======
   |  Pondage (daily storage)   |---> Spillway
   |_____________________________|
          |      |
          |      +--> Riparian release
       [Intake + trash rack]
          |
     [Desander / settling basin]
          |
   Headrace tunnel ==============\
                                  [Surge tank]
                                      |
                              Penstock |
                                      \|
                    [Powerhouse: MIV, Francis,
                     Generator, Governor, AVR]
                          |            |
                     Tailrace     GSU transformer
                          |            |
                       River      Switchyard -> Grid

Components and functions

ComponentFunction
Diversion dam / weir with gatesRaises water level, diverts water, forms pondage
PondageStores off-peak inflow for daily peaking operation
Spillway, undersluicePasses floods, flushes sediment
Intake with trash rackAdmits design flow; stops debris
Desander (settling basin)Removes fine sediment to protect turbines
Headrace tunnelConveys large discharge to the surge tank with low loss
Surge tankControls water hammer; supplies flow during load change
Penstock / pressure shaftCarries water under pressure to turbines
Main inlet valveIsolates each unit
Francis turbine + draft tubeConverts hydraulic energy to mechanical; draft tube recovers energy
GovernorControls speed/frequency and load
Synchronous generator + excitation/AVRGenerates power; controls voltage and reactive power
Generator CB, GSU transformerSwitching and step-up to transmission voltage
SwitchyardConnects plant to grid; isolation and protection
TailraceReturns water to the river
AuxiliariesStation transformer, DC system, diesel generator (black start), cooling, crane, SCADA

Why PRoR

It supplies the evening peak, which is valuable in Nepal, especially in the dry season (e.g. Kaligandaki A, Middle Marsyangdi are peaking ROR plants).

✓ Answer checked by Claude Opus 5.5 (high effort)

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