18-08-2012, 12:32 PM
Hydro-Turbine Power System
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INTRODUCTION
This report is based on a project which was given to us students by our subject lecturer. The objective of the project was simply to model a Hydro-Turbine Power System comparing Flow rate to the Generated Terminal Voltage (Vt). The project was to be presented in the form of an oral presentation by the group members but was later changed to a written presentation.
This written report will be therefore presented in the form compatible with the oral presentation so as to capture the initial objective of the project laid out to us by Mr.Evertz and also to highlight the extensive research done to overcome the challenges in designing, not an ideal, but practical Hydropower System.
Brief History Of Hydropower
Micro Hydropower (from hydro meaning water and micro meaning small scale)refers to electrical energy that comes from the force of moving water used topower a household or small village.The fall and flow of water is part of a continuous natural cycle. The sundraws moisture up from the oceans and rivers, and the moisture thencondenses into clouds in the atmosphere. The moisture falls as rain orsnow, replenishing the oceans and rivers. Gravity moves the water fromhigh ground to low ground. The force of moving water can be extremelypowerful, as anyone who has been whitewater rafting knows! MicroHydropower harnesses some of this power to create electricity.Hydropower is a renewable energy source because it is replenished by snowand rainfall.
PRINCIPLES OF HYPROPOWER
Hydropower plants capture the energy of falling water to generate electricity. A turbine converts the energy of falling water into mechanical energy. Then an alternator converts the mechanical energy from the turbine into electrical energy. The amount of electricity a hydropower plant produces is a combination of two factors:
1- How far the Water Falls (Head): Generally, the distance the water falls depends on the steepness of the terrain the water is moving across, or the height of a dam the water is stored behind. The farther the water falls, the more power it has. In fact, the power of falling water is ‘directly proportional’ to the distance it falls. In other words, water falling twice as far has twice as much energy. It is important to note we are only talking about the vertical distance the water falls – the distance the water travels horizontally is consequential only in expense of the system and friction losses. Head is usually measured in ‘feet’ or meters.
2- Volume of Water Falling (Flow): More water falling through the turbine will produce more power. The amount of water available depends on the volume of water at the source. Power is also ‘directly proportional’ to river flow, or flow volume. A river with twice the amount of flowing water as another river can produce twice as much energy. Flow volume is usually measured in ‘gallons per minute’, or ‘GPM’. For Micro Hydro systems, this translates into two categories of turbines: For high head and low flow volume sites, impulse turbines are the most efficient choice. The power produced by an impulse turbine comes entirely from the momentum of the water hitting the turbine runners. This water creates a direct push or ‘impulse’ on the blades, and thus such turbines are called ‘impulse turbines’. For low head and high flow volume sites, a reaction turbine is the best choice. The reaction turbine, as the name implies, is turned by reactive force rather than a direct push or impulse. The turbine blades turn in reaction to the pressure of the water falling on them. Reaction turbines can operate on heads as low as 2 feet, but require much higher flow rates than an impulse turbine.
IMPULSE TURBINE
For this project an impulse turbine was select because of its power range. An impulse turbine has a maximum capacity of about 1Kw and it uses a high head and low flow rate. In a system using an impulse turbine, water is diverted upstream of the turbine into a pipeline. The water travels through this pipeline to a nozzle, which constricts the flow to a narrow jet of water. The energy to rotate an impulse turbine is derived from the kinetic energy of the water flowing through the nozzles. The term ‘impulse’ means that the force that turns the turbine comes from the impact of the water on the turbine runner. This causes the attached alternator to turn, and thus the mechanical work of the water is changed into electrical power.
PELTON WHEEL
The Pelton wheel hydraulic turbine is driven by a jet of water issuing from anozzle and striking the buckets on the wheel causing it to rotate and thusdevelops a power output. This creates a torque on the wheel. The flow rate ofthe water jet is controlled by a spear valve. After the flow leaves the turbinecasing it empties into a hydraulic bench where its volume is measured alongwith the time using a digital timer. This will then give the volumetric flowrate through the turbine. The turbine wheel speed is measured by a digitaltachometer. The torque on the turbine wheel is measured by a brake systemwith spring balances.