Micro-processors helping to make windmills reliable

Press, 30 August 1984, Page 21

Micro-processors helping to make windmills reliable

Windmills have been turning for centuries — the Emperor Hammurabi considered using them for irrigation in the seventeenth century B.C. — but they are still being developed and refined. In the Electrical and Electronic Engineering Department of the University of Canterbury an experimental unit has even been fitted with a microprocessor for experiments to improve efficiency. But windmills, or wind turbines as they are known, have not been thrust into the electronics age at the whim of a researcher. The induction generator and microprocessor controlled rectifier fitted into the business part of the wind turbine at Ham are there for a specific purpose: to make the turbine reliable and more efficient in the special fields for which it has been designed.

Windmills have been controlled for many years by varying the pitch of the blades, but the response to changes in wind speed are sluggish. In any case, variable pitch blades are expensive. To overcome this special problem, lan Milner, who is undertaking doctoral research at Ham, has constructed a wind turbine without variable pitch blades. The characteristics of his fixed geometry wind turbine generation system are such that for any particular wind speed it is possible to gain maximum power transfer from the wind to the turbine shaft by adjusting the generator electrical load so that the shaft load and speed are controlled.

The advantage is relatively simple mechanical construction. Pitch control is eliminated, leading to fewer maintenance problems and possibly to a longer lifetime.

The turbine, mounted on a 15metre tower, consists of a threebladed trailing horizontal axis wind turbine six metres in diameter, coupled through a gearbox to a squirrel cage induction motor acting as a self-excited generator. This, along with controls, is mounted on a four-metre steel column.

Self-steering is achieved by the down-wind, or trailing design, but it can be steered for shut-down by a hydraulic drive at the base of the column with transmission by a shaft through the column. The hardware cost about $lB,OOO.

It is all rather a far cry from the giant wind turbines being used in Europe and the United States, such as the two-bladed turbine 130 metres in diameter and producing 7.3 megawatts which is expected to begin operating in Oahu early next year for the Hawaii Electric Company.

But it is being perfected for specific, principally rural, purposes. Dr D. B. Watson, a senior lecturer in electrical engineering, who is supervising Mr Milner’s research, describes the turbine as a small-scale autonomous wind energy conversion system.

the Electricity Division of the Ministry of Energy, hopes that the fixed pitch design will prove successful because it could then be used for very large turbines. Large wind generators are not easy to construct and pose special design problems the larger they become. The wind is slowed by friction with the ground at low level, but at higher levels it blows much faster. Thus the wind tends to drive a blade near the ground more slowly than a blade near the top of the arc. With propellers swinging through more than 100 metres, the

It is not intended, he says to supply power to the national grid, but to provide power for specific purposes mainly in rural areas — for heating glasshouses, fowlhouses, pigpens or cowsheds, or for domestic heating. Because it is not connected to the grid and because of the heating application, it does not need to generate at constant frequency and voltage. Mr Milner, who is on leave from

ERIC BEARDSLEY, information officer at the University of Canterbury, tilts at windmills in his third article of the series outlining how young engineers are being trained in the new high technology field of micro-electronics and the application of research at Ham in both industry and agriculture.

though small, could cause sewsije vibration problems. In addition, large blades flashing roundhand round might interfere withJfSTevision reception in nearby areas. “So in some places the tendency today is to think in terms of ‘farms’ of small turbines instead of one large windmill,” Mr Milner said. “Indeed, the British are thinking of installing small turbines at sea in places where the winds blow consistently. Power from the wind remains an attractive proposition in an energy-short world.”