Hydraulic Turbines

Submitted by

Manish Ranjan

12MEE0036

What Are Hydraulic Machines?

Machine which convert hydraulic energy( energy possessed by water) into mechanical energy (which is further converted into electrical energy)---turbine

Machine which convert mechanical energy into hydraulic energy---pump

Hydraulic Turbines

Hydraulic Turbines have a row of blades fitted to the rotating shaft or a rotating plate. Flowing liquid, mostly water, when pass through the Hydraulic Turbine it strikes the blades of the turbine and makes the shaft rotate. While flowing through the Hydraulic Turbine the velocity and pressure of the liquid reduce, these result in the development of torque and rotation of the turbine shaft.

Classification of Hydraulic Turbines: Based on flow path Based on pressure change Based on head Based on specific speed Based on disposition of turbine main shaft

Based On Flow Path Axial Flow Hydraulic Turbines: This category of

Hydraulic Turbines has the flow path of the liquid mainly parallel to the axis of rotation. Kaplan Turbines has liquid flow mainly in axial direction.

Radial Flow Hydraulic Turbines: Such Hydraulic Turbines has the liquid flowing mainly in a plane perpendicular to the axis of rotation.

Mixed Flow Hydraulic Turbines: For most of the Hydraulic Turbines used there is a significant component of both axial and radial flows. Such types of Hydraulic Turbines are called as Mixed Flow Turbines. Francis Turbine is an example of mixed flow type, in Francis Turbine water enters in radial direction and exits in axial direction.

Based On Pressure Change

Impulse Turbine: The pressure of liquid does not change while flowing through the rotor of the machine. In Impulse Turbines pressure change occur only in the nozzles of the machine. Example of impulse turbine: Pelton Wheel.

Reaction Turbine: The pressure of liquid changes while it flows through the rotor of the machine. The change in fluid velocity and reduction in its pressure causes a reaction on the turbine blades; this is where from the name Reaction Turbine may have been derived. Examples: Francis and Kaplan Turbines fall in the

category of Reaction Turbines.

Based On Head

High head turbine (Above 250 m) Pelton Turbine

Medium head turbine (60 – 250 m) Francis Turbine

Low head turbine (Below 60 m) Kaplan Turbine

Based On Specific Speed Specific speed  Ns =  N √P / H5/4

Low specific speed (8.5 – 30) - Pelton Turbine Medium specific speed (50 – 340) - Francis Turbine High specific speed (255 – 860) - Kaplan

Turbine

Based On Disposition Of Turbine Main Shaft Horizontal shaft Vertical shaft

Layout Of A Hydro Electric Power Plant

Parts Of A Hydroelectric Plant

Dam. Raises the water level of the river to create falling water. Also controls the flow of water. The reservoir that is formed is, in effect, stored energy.

Turbine. The force of falling water pushing against the turbine's blades causes the turbine to spin. A water turbine is much like a windmill, except the energy is provided by falling water instead of wind. The turbine converts the kinetic energy of falling water into mechanical energy.

Generator. Connected to the turbine by shafts and possibly gears so when the turbine spins it causes the generator to spin also. Converts the mechanical energy from the turbine into electric energy. Generators in hydropower plants work just like the generators in other types of power plants.

Transmission lines. Conduct electricity from the hydropower plant to homes and business.

Pelton Turbine/ Wheels

Water strikes the vanes along tangent of the runner and the energy available at the inlet of turbine is only kinetic energy, there fore is is a tangential flow impulse turbine

In a Pelton Turbine or Pelton Wheel water jets impact on the blades of the turbine making the wheel rotate, producing torque and power.

Main Parts Of A Pelton Wheel

Nozzle: it control the amount of water striking the vanes of the runner

Casing: it is used to prevent splashing of water and plays no part in power generation

Runner with bucket: runner is a circular disc on the periphery of which a number of evenly spaced bucket are fixed

Breaking jet: to stop the runner in short time breaking jet is used

Diagrammatic View of Pelton Turbine

Working Principle of Pelton Turbine Water jets emerging strike the buckets at splitter and split into two. Stream flow along the inner curve of the bucket and leave it in the

direction opposite to that of incoming jet. The high pressure water can be obtained from any water body

situated at some height or streams of water flowing down the hills. The change in momentum (direction as well as speed) of water

stream produces an impulse on the blades of the wheel of Pelton Turbine. This impulse generates the torque and rotation in the shaft of Pelton Turbine.

Horizontal shaft - Not more than 2 jets are used and Vertical shaft - Larger no. of jets (up to 6) are used.

Iron/Steel casing to prevent splashing of water and to lead water to the tail race.

Francis Turbine

1st hydraulic turbine with radial inflow Water flow from outward to inward, k/a inward radial

flow turbine Francis turbine is a reaction turbine as the energy

available at the inlet of the turbine is a combination of kinetic and pressure energy.

Water pressure decreases as it passes through the turbine imparting reaction on the turbine blades making the turbine rotate

Main Parts Of A Francis Turbine

Casing: the runner is completely enclosed in an air-tight spiral casing. The casing and runner are always full of water

Guide mechanism: it consists of stationary circular wheel on which stationary guide vanes are fixed. The guide vanes allow the water to strike the vanes of the runner without shock at inlet

Runner: is a circular wheel on which a series of curved radial guide vanes are fixed

Draft tube: it is used for discharging water from the outlet of the runner to the tail race.

Parts of Francis Turbine

Schematic View of Francis Turbine

Working Principle Of Francis Turbine

Francis Turbines are generally installed with their axis vertical.

Water with high head (pressure) enters the turbine through the spiral casing surrounding the guide vanes.

The water looses a part of its pressure in the volute (spiral casing) to maintain its speed.

Then water passes through guide vanes where it is directed to strike the blades on the runner at optimum angles. As the water flows through the runner its pressure and angular momentum reduces.

This reduction imparts reaction on the runner and power is transferred to the turbine shaft.

If the turbine is operating at the design conditions the water leaves the runner in axial direction.

Water exits the turbine through the draft tube, which acts as a diffuser and reduces the exit velocity of the flow to recover maximum energy from the flowing water.

Kalpan Turbine

Kalpan turbine is an axial flow reaction turbine

The water flows through the runner of the turbine in an axial direction and the energy at the inlet of the turbine is the sum of kinetic and pressure energy.

In an axial flow reaction turbine the shaft is vertical.

Lower end of shaft is k/a hub or boss.

On the hub vanes are attached. If the vanes are adjustable then it is k/a kalpan turbine, if vanes are not adjustable then is k/a propeller turbine

Best suited where large quantity of low head water is available.

Kaplan Turbine has propeller like blades but works just reverse. Instead of displacing the water axially using shaft power and creating axial thrust, the axial force of water acts on the blades of Kaplan Turbine and generating shaft power.

Main Parts Of A Kalpan Turbine

Scroll casing Guide vane mechanism Hub with vanes Draft tube

Schematic View of Kalpan Turbine

Working Principle Of Kalpan Turbine

The working head of water is low so large flow rates are allowed in the Kaplan Turbine.

The water enters the turbine through the guide vanes which are aligned such as to give the flow a suitable degree of swirl determined according to the rotor of the turbine.

The flow from guide vanes pass through the curved passage which forces the radial flow to axial direction with the initial swirl imparted by the inlet guide vanes which is now in the form of free vortex.

The axial flow of water with a component of swirl applies force on the blades of the rotor and looses its momentum, both linear and angular, producing torque and rotation (their product is power) in the shaft.

The scheme for production of hydroelectricity by Kaplan Turbine is same as that for Francis Turbine.

Draft Tube

It is a pipe of gradually increasing area which connects the outlet of the runner with the tailrace.

One end of the draft tube is connected to the outlet of the runner while the other end is submerged below the level of water in the tailrace

It creates a negative head at the outlet of the runner thereby increasing the net head on the turbine

It converts a large proportion of rejected kinetic energy into useful pressure energy

Governing of Turbines

It is the operation by which the speed of the turbine is kept constant under all conditions of the working load. This is done automatically by a governor which regulate the rate flow through the turbine according to the changing load condition on the turbine

It is absolutely necessary if the turbine is coupled to an electric generator which is required to run at constant speed under all fluctuating load conditions