Turbine And Head.docx

1

HYDRUALIC TURBINE AND TYPES ON THE BASIS OF HEAD TURBINE DEFINITION A turbine is a rotating part which converts kinetic energy of a working fluid into useful mechanical energy and/or electrical energy. Simple, right? Well, nothing is simple when you go deeper. There are set of blades mounted on a rotor which helps in extracting energy from the moving fluid. The efficiency of turbines depend on the design of the blades. Different applications need different designs & designing them isn’t a layman’s job.

Turbines used in hydro power plants The turbines used in hydroelectric power plants are water turbines which have water as their working fluid. First of all, millions of liters of water is collected in the dam. More the height of dam, more the pressure. The highly pressurized water is then made to flow via large pipe called as penstock. The turbine is located at the end of penstock from where the pressurized water strike the blades of turbine at high velocity making it to rotate. This turbine is connected to a generator which generates electricity. The shape of turbine blades depend upon the pressure & velocity of water. Water turbines are classified into 2 types1. Impulse type 2. Reaction type

Impulse type turbines Impulse turbines basically work on Newton’s 2nd law. In impulse turbines, number of elliptical half sized buckets are fitted instead of blades on the rotor hub. When water strike the buckets at high speed, the rotor starts rotating. In short, the kinetic energy of water gets converted into rotational mechanical energy ! Thus electricity is generated when one end of turbine shaft is connected to generator ! Example – Pelton turbine

2

Reaction turbines The turbine blades or the impeller blades are designed in such a way that a force is generated on one side when water flows through it just like an airfoil. The force produced by airfoil is responsible for lift of aero plane. Similarly here, that force makes the blades rotate. Example – Kaplan turbine Different types of turbines have their own ideal operating conditions. For eg. Pelton turbines are preferred where low discharge rate can be obtained & high head(801600m) is available. Kaplan turbines require high discharge rate along with low or medium head(2-70m). Francis turbine work on medium flow rate & medium head. Francis turbine is a combination of impulse & reaction turbine. Francis turbines are most widely used turbines because they offer the highest efficiency & could also work in wide range of operating conditions. 1m head of water = 9810 Pa (100m of head is almost 7 times of atmospheric pressure) TYPES OF TURBINE ON THE BASIS OF HEAD OF WATER There are three types of turbines on the basis of head 1. High head turbine 2. Medium head turbine 3. Low head turbine

HIGH HEAD TURBINE The cost of drive train is closely related to how much torque it has to transmit, so higher heads = less torque = less cost. Of course you only have what you have, so if your site only has 2 ½ metres of head you won’t be able to increase this significantly. However, even small increases in head can make a difference. Sometimes it is possible to clear silt or re-grade a tailrace or discharge channel to lower the downstream water levels slightly which increases the overall head at the site. Or it may be possible to raise the water level on the upstream side by raising weir crests or sluices, though this must be done carefully to avoid increasing flood risk, and sometimes requires the construction of new spillways or installation of fail-safe tilting weirs to ensure that flood risk isn’t increased during extreme flood events.

3

Generally speaking the cost of even small increases in head at low-head sites is repaid hundreds of times over from increased energy production for the next few decades, so is always worth the effort.

MEDIUM HEAD TURBINE Nautilus builds three different medium head designs. An open flume setting is not a practical choice on heads over 3.7m (12ft). On higher head sites the water is brought to the turbine under pressure with a penstock or pipe. The Nautilus MH line of turbines are fitted with stainless steel scroll cases or round pressure cases. The CMC-MH and T-MH turbines are sized to bolt to a 300mm (12in) penstock. The 660-MH and 440-MH models accept a 200mm (8in) connection.

Nautilus' Medium Head Turbine Line: The T-MH is the most powerful of our turbines to date. It is an unregulated design and needs to be sited where there is sufficient flow for operation, or combined with the CMC-MH which is designed for flow control. The CMC-MH is a simple ‘register gate’ turbine that will operate on heads up to 12.2m (40ft). The gates in this design allow for actuator controls to match available flow and turn the unit on and off automatically. The 440-MH and 660-MH turbine models are the smallest and highest head Francis turbines built by Nautilus. They operate at heads as high as 18.3m (60ft). A simple cylinder gate regulator allows for actuator control.

LOW HEAD TURBINE Hydropower captures energy as water moves from a higher area to a lower area. In Canada, low head hydro generally refers to hydro projects where the vertical difference in the high water and low water (referred to as “head”) is less than 15 m, and very low head hydro refers to those with a head below 5 m. In comparison to “conventional” hydro where a large portion of the potential resource has already been exploited, Canada has abundant untapped resources for low head hydropower development, with over 5,000 MW of identified potential.

There are many advantages to developing low head hydro:  

Like most hydro technologies, the output is predictable; it is therefore one of the most reliable renewable resources for electricity generation In many cases, low head hydro generation can be added where low head dams and other hydraulic structures already exist for flood control, irrigation, and water regulation

4

 

It requires a smaller impounded area than large hydro projects and therefore has less environmental impact It can help Canada increase its use of clean power, particularly in remote locations where diesel generation is currently the primary source of electricity

Economic feasibility is currently the most important factor in the development of a low head sites as lower head means lower power output per unit of flow. Low head hydro needs to move greater volumes of water if it is to produce the same amount of electricity as conventional hydro. Conventional hydro turbine technology requires larger equipment and larger civil structures than low head hydro turbines, resulting in higher development costs. As such, conventional hydro technology cannot provide an economically viable solution. Until 2010, Can met ENERGY worked with universities and the hydro industry to undertake research and development in new technologies to make potential low head sites more economically viable. Examples of these innovations include a variable-speed turbine system with reduced production and installation costs, as well as a specific very low head turbine design that significantly reduces the cost of on-site civil infrastructure.