Wednesday, July 6, 2011

Wind Turbine Rated Power

Wind Turbine Rated Power – Wind turbine are basically rated in terms of how much power they can produce at a particular wind speed. Most manufacturers if not all will rate their wind turbines at a particular wind speed.

If you take a look at a wind turbine power curve below you would notice that the Y-axis has values starting from zero Kilowatt to some maximum Kilowatt value. These Power rated value are usually the turbine output  power that corresponds to different wind speed values on the X-axis.
Wind Turbine Power Curve

However, this is not the wind turbine rated power. Usually the manufacturer will rate the output power at around 50%-75% of the maximum power output of the alternator and would consider that point to be the wind turbine rated power. Having said that, it means that the wind turbine can produce more power than its rated power. But, why is that?

There is a reasonable explanation why manufacturers rate their turbines lower than the maximum output power. The wind speed is never constant at the same particular value; rather it is fluctuating all the time. Sometimes wind speed with small fluctuation can’t be noticed and some other times large fluctuation can be noticed.

For small fluctuating wind speed, the power output from the wind turbine would stay around the average wind speed of that location, however; for large fluctuating wind speeds, the power output can reach the maximum peak value and even exceed that point.

It is interesting to know that when the wind speed exceeds the maximum peak value its output power starts to drop down and can bring the output power to the wind turbine rated power value or even below. However, if the wind speed becomes excessive, the wind turbine has to protect itself by applying the internal breaking system to slow down the turbine blades and prevent damage to its equipments.


To simplify things, look at the wind turbine power curve in the graph below. You will notice that the wind turbine rated power is around 6.5 kilowatts at 8.5 meters per second (the red lines). While the maximum output power (peak power) is 10 Kilowatt accruing at around 10.5 meters per second (dotted pink line).

However, if wind speed increases without being turbulent (above 17 m/s), the output power will start to drop down as the wind speed increases till it reaches a pre-assigned value (6 Kilowatts) by the manufacturer. At that point the wind turbine will apply its internal breaking system to slow down the wind turbine from over speeding (to the right of blue dotted line).
Wind Turbine Rated Power Graph

Note that the wind turbine breaking system of the wind turbine are applied in case of over speeding in order to keep the output power near the wind turbine rated power but on the upper limit of the power curve.

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