Palmer Putnam's 1.5 MW Wind Turbine

This article was initially published in Today's Engineer on May 2013

Supplying electrical power generated from wind to the commercial supply grid has a long history. Although wind power began to make great strides towards industrial scale installations in the late 1970s and 1980s, many of the technical obstacles had been addressed in the 1930s. Wind power’s current success owes much to pioneers who built wind generators and solved many engineering problems in the years prior to World War II. One of the major obstacles in attaching wind generators to an alternating current power grid was synchronizing the generator to the frequency of the grid, in part by smoothing out the variations in wind speed. Prior to the 1930s, small wind generators had supplied electricity for local consumption, especially in rural Canada and the United States, where they were especially popular with farmers. As early as 1888, Charles Brush had powered his laboratory in Cleveland, Ohio with a 12.5 kilowatt DC wind generator.

In 1933, at Balaclava, Crimea (near the scene of the famous 1854 charge of the light brigade), V. N. Krasnovsky and his engineers built a 100-kilowatt wind generator on a twenty-five meter high tower. Harvesting the winds blowing in off the Black Sea, it generated DC electricity which synchronous converters transformed into AC and allowed three-phase current to be fed into the grid. At the time the Crimean turbine was built, it was the most powerful wind generator in the world. It operated for ten years, but was dismantled during World War II when it failed.

In the U.S.A., Palmer C. Putnam (1900-1984) realized that – in order to generate power from the wind efficiently and economically – location was vital, and the turbine would need to be larger than those then being used on farms and in rural locations. He sought sustained wind speeds in excess of 30 mph (48 kph) and he wanted to be able to supply alternating current to the grid without the losses incurred by converting direct current to alternating current. In the mountains of Rutland, VT, U.S.A., Putnam found a place that was —to use his phrase from his patent— “advantageously exposed” called Grandpa’s Knob, a 1976ft (600 meter) high forested summit with a rocky base. Grandpa’s Knob has strong, but generally not too irregular winds. There, during the winter of 1940-1941, workers built the 120 foot (36 meter) tower and turbine.

The design and the scale were daring. The two steel blades of the turbine weighed 7.5 tons or 6818 kg. each and were 66 feet (20 meters) long —bigger than the wings of all but a handful of bombers flying at the time. The turbine was designed to operate in wind velocities between thirty and sixty miles per hour (48 and 96 kph) and to withstand gusts stronger than 140 mph (225 kph). The generator was designed to produce 1.5 megawatts, fifteen times more than the largest wind generator then in existence.

The genius of Putnam’s design lay in the ways his turbine could be adjusted to the varying speed of the wind, thus keeping the generator speed within the ranges that would keep it synchronized with the line. Electric control circuits controlled relays and motors which changed the pitch and the coning of the blades. The blades could be “coned” meaning that they could be angled forward or back instead of remaining perpendicular to the turbine shaft in order to change their exposure to the wind. This was particularly useful in coping with gusts. Either of the two blades could cone independently to allow for the difference in wind gusts encountered by the blade close to the ground versus the gusts encountered by the blade at the top of the arc. The pitch of the blades could also be changed in response to wind velocity to keep the turbine synchronized with the line, and the axis of rotation of the entire turbine could be angled forward and downward.

Frequency-matching circuits placed the generator on the line when properly synchronized with the power line frequency and then gradually loaded the generator. If the wind velocity either decreased so much that the turbine could not turn fast enough to synchronize with the line, or increased so much that the turbine was too fast, the circuits would remove the generator from the line.

On 19 October 1941 the turbine began supplying power to the lines of the Central Vermont Public Service Corporation. In the course of 695 operating hours, it produced 298,240 kilowatt hours of electricity.

On 26 March 1943, one of the two turbine blades broke off and crashed partway down the side of the mountain. With metals in short supply because of World War II, the turbine was not considered a priority and was not rebuilt. However, the knowledge gained and the technical solutions that Putnam worked out would prove extremely important decades later when wind power began to become commercially important.

Video

A video clip of the turbine in action

Palmer Putnam's 1.5 MW Wind Turbine

Video

Further Reading