Where it all began
Most early turbines were water wheels.
Water power has been exploited since ancient times. The Egyptians had a simple water wheel in 4 BC for irrigation purposes. In the Helenistic period, more sophisticated compartmentalized wheels were developed after 3 BC and the Romans developed them further. The early water wheels were used for lifting water (like pumps) to drain mines or lift water from rivers to irrigate fields. The first evidence of a geared water wheel being used to extract power from water is dated around 1 BC.
Water wheels became common in early medieval history and by the time of the Doomsday Book (the census of 1086 AD) there were 6000 water mills in England alone.
Most of these were grist mills (used for grinding corn), but there were also weaving mills, saw mills, fulling mills, hammer mills and many others.
Mills were driven by three basic types of water wheel:
- overshot wheels, in which a flume supplies water to the top of the wheel downstream of the highest point Take a look at the animation below);
- breast wheels, in which the wheel acts as a dam and is turned by water flowing down the upstream face of the wheel and beneath it; and
- undershot wheels, in which water is supplied by a flume or canal to the lower half of the wheel and flows beneath it..
Waterwheels were usually set up to be turned by a stream, canal or flume. The axel of the wheel was connected to pulleys and belts to drive the mechanical equipment in the mill.
Water wheels were valuable sources of power for centuries, but the industrial revolution brought increased demand for power. Mills could not always located near the best sources of hydropower.
The breakthrough came in 1831, with the invention of the first electromagnetic generator by the British scientist Michael Faraday – the Faraday disk. This led to the rapid development of more advanced electric generators. Now power could be generated at one location and transmitted by electrical conductors to be used at another location.
At the same time, the size of water wheels was increasing, but there was an economical limit to the hydraulic head and flow rate they could use. The search began for larger capacity machines – a search made possible by improvements in scientific understanding, manufacturing methods, and materials.
The father of the modern hydraulic turbine is thought to be Johann Segner who developed a horizontal-axis reactive water turbine in the mid-18th century. This was followed by a series of turbine inventions, which included both inward-flow and outward-flow turbines. Inward flow turbines became more popular as they allow a better arrangement of the turbine components.
In 1849, James B. Francis developed the first modern water turbine by designing an inward flow reaction turbine with an efficiency of over 90%. The Francis turbine is still the most widely used water turbine in the world today, mainly because the design can be adapted to a large range of hydraulic heads and flow rates.
The next most common type of turbine is the impulse turtbine. If you spray water into the tire of a wheel, you can make it rotate. That’s more or less how an impulse turbine works. The first modern impulse turbines were inspired by the power of water jets used for mining in California’s gold fields. Pipelines, supplied with water from intakes high above the gold workings, had enormous pressure. Nozzles on hoses connected to these pipelines converted the potential energy of the water to kinetic energy and could be used to excavate the ore and sluice it to a collection point. In 1866, Samuel Knight directed such nozzles at the perimeter of a bucketed wheel to produce mechanical power.
Lester Pelton improved the efficiency of the Knight Wheel in 1879, by replacing the single buckets with double buckets that directed the outflow away from the wheel.
This became the de-factor design for impulse turbines, and it is still common to call impulse turbines “Peltons”. In fact, William Doyle improved Pelton’s bucket design in 1895 with a cut-out that allowed the jet a cleaner bucket entry and boosted efficiency to around 92%. He took over the Pelton company, but kept the name.
The Turgo and Cross Flow turbines (pictured below) are later impulse turbine designs that have good efficiency for intermediate and low heads and flows.
The Turgo turbine was developed in 1919 as a modification of the Pelton by Gilkes (now Gilbert Gilkes & Gordon Ltd. of Britain). Turgo runners are more compact and less expensive than a Pelton designed for the same flow and still have a high efficiency, making them a good choise for small hydro installations if the head and flow range are suitable.
The cross flow turbine was developed by Anthony Michell, patented in 1903, and manufactured for many years. It was developed further by Donát Bánki and then by Fritz Ossberger, who patented the “Cross Flow Turbine” 1933. Ossberger’s company is the leading manufacturer of this type of turbine. It suits low heads and high flows. The length of the cylindrical runner wheel is normally split into two parts, with the smaller part about half the length of the larger. The regulator can direct water to either part or to both, so while the efficiency is lower than a Pelton, it has a long, flat efficiency curve and can operate down to 1/6th of the rated design flow. Cross flow turbines are also relatively cheap and therefore ideal for small hydro and mini-hydro.
You can read more about modern turbines and operating ranges on the Generating Equipment Page.