Head works

Structure at the intake of the tunnels and flumes

They have Booms Trash racks Sluices for passing debris Gates and valves for controlling the flow

Booms Divert ice and floating logs from intake Consists of logs tied end to end and form a floating chain to diverts floating matter to a by-pass chute

Trash racks Remove floating or submerged debris directly at the intake entrance. Placed across the intake structure to keep out floating matter from going through the penstock.

They form a screen of oarallel bars welded to cross members and supported by beams Spacing of bars varies from 1.5 to 15cm or more Smaller the spacing greater the safety Gates control the rate of water flow entering

Low pressure intake with headworks

High pressure or high headworks

Gates like Cylindrical Spherical Butterfly of needle valves are used for water control These gates are used at headworks penstocks turbine inlets

Conduits Headrace Tail race Leads water from headwork to turbine Leads water rom turbine outlet ot downstram side of plant

Conduits Open type Closed type flumes Canals tunnels Pipe lines penstocks

Flumes It’s an artificial water channel of wood, metal , concrete or masonry supported above the surface of the ground. Used when its expensive to construct canals Commonly used to cross a depression or difficult terrain

Usually rectangular or semi circular type Bench flumes--- flumes that are directly supported on ground

Wooden flume

Steel flume

Concrete flume

Concrete flumes have longer life Low maintenance cost Wooden flumes have shorter life

Tunnels Water carrying tunnels Service tunnels --- dry tunnels Diversion tunnels To divert water away Head race or power tunnels Carry water to power house These are pressure tunnels Tail race tunnels carry water away from the power house

Cross section of tunnels Circular or horse shoe when water flow is full tunnel acta as a pressure conduit These tunnels are to be lined Steel or concrete liner is necessary to prevent collapse if tunnel material is weak During partial flow acts as open channels No need for lining

Forebay Water carried by the power canals is distriuted to various penstocks through forebay Forebay is also called head pond Water is temporarily stored in case of load rejection Water is withdrawn when load increases Acts as a regulating reservoir

Forebay is created at the end of the power canal by widening it into a small basin Constructing a small dam across the natural flow The excess water accumulated is discharged by spillways

Main Parts of a typical forebay Entrance bay or basin Spillway Flushing device Screens Valve chamber Conduit or penstock inlet

Penstock Pipe connecting forebay or surge tank to turbine Pressure conduit

Choice of penstock materials Depends on Head Topography of terrain Discharge to be handled

Materials Steel Rcc Asbestos cement Wood Cast steel

Sharp bends to be avoided They cause loss of head Require special anchorages Anchorage prevents penstock movement due to dynamic forces