Hydraulic Machines
Hydro-Electric Plant
INTRODUCTION
The purpose of the Hydro-Electric Plant is to harness power from water flowing under pressure. Water flowing under pressure has two forms of energy - Kinetic and Potential. These kinetic and potential energy possessed by water is converted into mechanical power by Hydraulic Turbine. The hydraulic turbine is, thus, a prime mover which when coupled to a generator produces electric power. Hydro-Electric Projects may not be used exclusively for power generation. Sometimes, they are the offshoot of flood control and irrigation projects and are known as "Multipurpose Projects".
HEAD
Head is the difference in elevation between two levels of water. It can be characterized as :(a) Gross Head and (b) Net or Effective head.
(a) Gross Head
It is defined as the difference in elevation between the head race level at the intake and the tailrace level at the discharge side, naturally, both the elevations have to be measured simultaneously. The gross head may vary as both the elevations of water do not remain the same at all times.
(b) Net or Effective Head
It is the head obtained by subtracting all the losses from the gross head in carrying water from the headrace to the entrance of the turbine. These losses are due to friction occurring in tunnels, canals, and penstocks which lead the water into the turbine.
ESSENTIAL COMPONENTS OF HYDROELECTRIC
(1) Storage Reservoir:
The storage reservoir may be natural or artificial.
Natural - Lakes, Mountains.
Artificial - Dam constructed across a river valley.
(2)Waterways and their control work:
A waterway is a passage through which water is carried from the storage reservoir to the powerhouse. It consists of a tunnel, canal, flumes, forebays, penstocks, etc.
(a) Forebays: It is an enlarged section of a canal spread out to accommodate the required width of the intake.
- It is provided with an intake structure, to direct water into the penstocks.
- Intake should be provided with trash racks so as to prevent the entry of debris into the penstock and thus avoid the possible damage to turbine runners.
- Its function is to store temporarily the water rejected by the plant when the electrical load is reduced and also to meet the instantaneous increased demand for water due to a sudden increase in load.
(b) Surge Tank: It is a reservoir fitted at some opening made on a long pipeline to receive the rejected flow when the pipeline is suddenly closed.
- It also helps in absorbing the sudden pressure rise due to closing of the valve when the load on the turbine is reduced thus eliminating the water hammer effect.
- When it is not possible to provide forebay we provide a surge tank to absorb pressure fluctuation.
- It reduces the distance between the turbine and the free surface.
- Long penstock should be provided with a surge tank so that water hammer pressure could be dissipated.
(3) Hydraulic Turbines:
(4) The Power House :
A powerhouse is a building consisting of a substructure to support the hydraulic and electrical equipment and a superstructure to house and protect this equipment.
(5) The Draft Tube :
It is a conduit that connects the outlet of a reaction turbine runner to the tailrace.
(6) The Tailrace :
It is a waterway to conduct water discharged from turbine to a suitable point where it can be safely disposed of or stored to be pumped back into the original reservoir.