PELTON WHEEL AND FRANCIS TURBINE GUIDED BY KRUNAL PATEL Prepared by Harshul Bhatia 130050119010 Kalp Bhatia 130050119011 Kevin bhagat 130050119505

Pelton wheel It is impulse , tangential flow, high head and law specific turbine. It require comparatively less quantity of water. A pelton wheel name after the American engineer lester pelton who contriute much to its development. The energy available at inlet is only kinetic energy.

Types of Impulse turbine: Water wheel : A water wheel is a machine for converting the energy of free-flowing or falling water into useful forms of power . A water wheel consists of a large wooden or metal wheel, with a number of blades or buckets arranged on the outside rim forming the driving surface . Most commonly, the wheel is mounted vertically on a horizontal axle , but the tub or Norse wheel is mounted horizontally on a vertical shaft.

Main parts of pelton wheel Nozzle and flow regulating arrangement(spear) a nozzle is a conical guide mechanism, which guide the water to desire path. It also regulate the flow of water.this water in the form of jet strike the vanes.. A conical spear operates inside the nozzle in an axial direction. The function of spear is to control the quantity of water through the nozzle. When the spear push forward into the nozzle it reduce the area of jet, and then quantity of water flowing through jet is reduced. When spear is pull back of the nozzle, the quantity of water is increased.

2 . Runner and buckets A runner is a circular disk fixed to horizontal shaft. on the periphery of the runner, a number of bucket are fixed uniformly. The shape of bucket is of a double hemispherical cup or bowl. Each bucket is divided into 2 symmetrical parts by dividing wall is called splitter. The purpose of splitter is to split water jet in two equal parts without shock each part of the jet flows sides ways round the smooth inner surface of the bucket and leaves it with a relative velocity almost opposite in direction to original jet. When the bucket is exactly hemispherical cup, the jet gets deflected through an angle 180˚, and maximum driving force will be exerted on the runner. For high head turbine, bucket are made of bronze, stainless steel or alloys, but for low head turbine it may made of cast iron. The surface of bucket is very smooth.

3. Casing the function of casing in pelton turbine is to prevent splashing of water, guides the water to flow to tail race & provides safety against accidents. In impulse, the static pressure of water is atmosphere throughout turbine and hence casing of pelton wheel has no hydraulic function to perform.

4. Breaking jet This is used when it is required to stop the turbine suddenly, water flow through main nozzle is stopped, but turbine rotates at higher speed because of inertia. Therefore, breaking jet directed through break nozzle opposite to the direction of rotation. This produces breaking torque on the bucket and stops the runner immediately.

5. Penstock it is large sized pipe or conduit which conveys water from the high level reservoir to the inlet of turbine. Penstock is made of steel, concrete or wood depending on head and quantity of water requires.

The water from dam is brought to the turbine inlet through pipes ending in one or more fixed nozzles. The entire pressure energy is of water is converted into the kinetic energy of water jet in nozzle. The water jet then strikes the blade of the runner and loose its all kinetic energy. The static pressure at inlet of turbine is equal static pressure at outlet of turbine. The rotation of wheel in impulse turbine is caused purely due to tangential force created by the impact of the jet and therefore is called impulse turbine.

Velocity triangles

Francis turbine The Invention Studying the boyden turbine francis was able to redesign it to increase efficiency. Constructing turbines as “sideways water wheels,” francis was able to achieve an astounding 88 percent efficiency rate. After further experimenting, francis developed the mixed flow reaction turbine which later became an american standard. Twenty-two of the “francis turbines” reside in hoover dam to this day. His work on these turbines was later published as the lowell hydraulic experiments in 1855.

Various components Spiral Casing : The fluid enters from the penstock to a spiral casing which completely surrounds the runner. This casing is known as scroll casing or volute. The cross-sectional area of this casing decreases uniformly along the circumference to keep the fluid velocity constant in magnitude along its path towards the stay vane/guide vane. Penstock Scroll casing Guide blades Governing mechanism Runner

Francis turbine It is a reaction turbine developed by an english born american engineer, sir J.B. Francis. The water enters the turbine through the outer periphery of the runner in the radial direction and leaves the runner in the axial direction, and hence it is called ‘mixed flow turbine’. It is a reaction turbine and therefore only a part of the available head is converted into the velocity head before water enters the runner. The pressure head goes on decreasing as the water flows over the runner blades. The static pressure at the runner exit may be less than the atmospheric pressure and as such, water fills all the passages of the runner blades. The change in pressure while water is gliding over the blades is called ‘reaction pressure’ and is partly responsible for the rotation of the runner. A francis turbine is suitable for medium heads (45 to 400 m) and requires a relatively large quantity of water.

Francis turbine

Francis turbine

The Francis Runner Traditional runner X blade runner

Francis Turbine Power Plant : A Continuous Hydraulic System

Spiral Casing