In a Pelton
Turbine or Pelton Wheel water jets impact on the blades of the turbine
making the wheel rotate, producing torque and power. Learn more about
design, analysis, working principle and applications of Pelton Wheel
Turbine.
Hydraulic
Turbines are being used from very ancient times to harness the energy
stored in flowing streams, rivers and lakes. The oldest and the simplest
form of a Hydraulic Turbine was the Waterwheel used for grinding
grains. Different types of Hydraulic Turbines were developed with the
increasing need for power. Three major types are Pelton Wheel, Francis
and Kaplan Turbine.
Design of Pelton Wheel Turbine
The
Pelton Turbine has a circular disk mounted on the rotating shaft or
rotor. This circular disk has cup shaped blades, called as buckets,
placed at equal spacing around its circumference. Nozzles are arranged
around the wheel such that the water jet emerging from a nozzle is
tangential to the circumference of the wheel of Pelton Turbine.
According to the available water head (pressure of water) and the
operating requirements the shape and number of nozzles placed around the
Pelton Wheel can vary.
Working Principle of Pelton Turbine
The
high speed water jets emerging form the nozzles strike the buckets at
splitters, placed at the middle of a bucket, from where jets are divided
into two equal streams. These stream flow along the inner curve of the
bucket and leave it in the direction opposite to that of incoming jet.
The high speed water jets running the Pelton Wheel Turbine are obtained
by expanding the high pressure water through nozzles to the atmospheric
pressure. 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. To obtain the optimum output from the Pelton Turbine the
impulse received by the blades should be maximum. For that, change in
momentum of the water stream should be maximum possible. That is
obtained when the water stream is deflected in the direction opposite to
which it strikes the buckets and with the same speed relative to the
buckets.
Pelton Turbine Hydroelectric Setup
A
typical setup of a system generating electricity by using Pelton
Turbine will have a water reservoir situated at a height from the Pelton
Wheel.
The water from the reservoir flows through a
pressure channel to the penstock head and then through the penstock or
the supply pipeline to the nozzles, from where the water comes out as
high speed jets striking the blades of the Pelton Turbine. The penstock
head is fitted with a surge tank which absorbs and dissipates sudden
fluctuations in pressure.
For
a constant water flow rate from the nozzles the speed of turbine
changes with changing loads on it. For quality hydroelectricity
generation the turbine should rotate at a constant speed. To keep the
speed constant despite the changing loads on the turbine water flow rate
through the nozzles is changed. To control the gradual changes in load
servo controlled spear valves are used in the jets to change the flow
rate. And for sudden reduction in load the jets are deflected using
deflector plates so that some of the water from the jets do not strike
the blades. This prevents over speeding of the turbine.