Different types of Turbines

 Turbine 

Turbine is the main equipment in the hydro power plant  that converts energy of falling water into rotating shaft power, means it converts kinetics energy of water into rotating shaft mechanical energy . There are different classification and types of Turbines are available.

                  The  proper selection of turbine for hydro-site or hydro power plant depends upon head and flow available. Generally, turbines  are  of two types, 

On the basis of action on moving blades; 

1. Impulse turbine 

2. eaction turbine.

1. Impulse Turbine

This turbine is never immersed in water but operates in air, driven by jet (jets) of water striking the rotor blade. The nozzle of penstock converts head of water from fore-bay tank into high speed jet that hits the turbine runner blades. Thus, turbine starts to rotate.

             This type of turbine is cheaper than reaction turbine because there is no need of pressure casing. It is widely used in micro-hydro applications rather than reaction turbine because they have several advantages like; simple design, easy to fabrication and maintain greater tolerance towards sands and other particles in water and better part load efficiency.

This type of turbine is suitable for high head only but not for low head sites because they have lower specific speed and to couple it to a standard alternator, the speed would have to be increased to greater extent. It's types are explained below;

a).Pelton Turbine

The basic principle of pelton turbine is simple. When a high speed water jet injected through a nozzle hits the buckets of pelton turbine and induces the impulse force. This force make turbine rotate. The rotor shaft runs generator and produce 

electricity.

         A pelton turbine consists of special shaped buckets mounted on the periphery of circular dice. It is turned by the force of water jet which is discharged through nozzle and hits the buckets. 

              The buckets are splinted into 2 halves so that central area doesn’t acts as dead spot incapable of deflecting water away from coming on jet. The bucket is designed to deflect jet through 1650 which is maximum angle. 

b).Turgo turbine 

Turgo turbine is an impulse turbine designed for medium head. Turgo installations are usually preferred for small hydro scheme where low is important. Water potential energy is converted in kinetic energy with penstock and nozzle. High speed water jet is then directed on turbine blade which deflect and reverse the flow and water exists little energy.

c).Cross-flow Turbine

Cross-flow turbine has a drum-shaped runner consisting of two parallel discs connected together near their rims by series of curve blades. A cross-flow turbine always has its runner shaft horizontal. In cross flow turbine, water passes through turbine transversely or across turbine blades. As with a water wheel, water enters at turbine's edge. After passing the runner, it leaves on the opposite side. The crossflow turbine generally operates at low speed. It is used for wider range of heads overlapping those Kaplan, Franchis and Pelton, operates in the head between 1-

200m. 

2.Reaction turbine

In reaction turbine, there is pressure change (lowers) of water when it passes through the rotor. So, it uses both pressure energy and kinetic energy. So, it is known as reaction turbine.

a).Franchis turbine

*. Radial flow reaction turbine with fixed runner blades and adjustable guidevanes used for medium head.. Water curves out axially

*. Turbine consists of spiral casing.

*. Low pressure in existing side of turbine may cause cavitations. So draft tube is used to discharge fluid. It converts dynamic pressure to static pressure by increasing area and reduce cavitations problem. 

The Francis turbine is a type of reaction turbine, a category of turbine in which the working fluid comes to the turbine under immense pressure and the energy is extracted by the turbine blades from the working fluid. A part of the energy is given up by the fluid because of pressure changes occurring in the blades of the turbine, quantified by the expression of degree of reaction, while the remaining part of the energy is extracted by the volute casing of the turbine. At the exit, water acts on the spinning cup-shaped runner features, leaving at low velocity and low swirl with very little kinetic or potential energy left. The turbine's exit tube is shaped to help decelerate the water flow and recover the pressure. 

b).Kaplan or Propeller Turbine 

Axial flow turbine, generally used for low head and high flow rate. 

 Kaplan is special type of propeller turbine which has adjustable runner blade and may or may not have adjustable guide vane. 

 Flow enters radial inward and makes right angled turn before entering runner  in axial direction. 

 Low pressure in existing side of turbine may cause cavitations. So, draft tube is used for discharging fluid. 

The Kaplan turbine is an inward flow reaction turbine, which means that the

working fluid changes pressure as it moves through the turbine and gives up its

energy. Power is recovered from both the hydrostatic head and from the kinetic

energy of the flowing water. The design combines features of radial and axial turbines.

The inlet is a scroll-shaped tube that wraps around the turbine's wicket gate. Water

is directed tangentially through the wicket gate and spirals on to a propeller shaped

runner, causing it to spin.

The outlet is a specially shaped draft tube that helps decelerate the

water and recover kinetic energy.