Apr18-13, 03:21 AM
I'm sure there is a simple answer to the following question that's got me thinking lately but I'm unsure (it's more of a hypothetical question out of interest and not homework).
If a simple older type fixed speed wind induction generator was connected directly to the grid via a gearbox and a transformer (as per attached diagram) and if the wind speed = 0 m/s, would the generator then act as a motor rotating the blades with an electrical frequency locked to the grid's frequency?
Based on torque-slip characteristic, if the stator leads the rotor with a positive slip (which is the case here), then you have a motor. Would this mean that the windmill now consumes electricity from the grid it's meant to be supplying?
Also, how do older windmills keep the rotor at a constant speed when there are no electronics to for control? What happens at higher wind speeds? Would the electrical frequency then go out of sync with the grid?
My understanding is that the blades are designed to spin at certain wind speeds. Any faster and the turbulence effect kicks in causing the blade to stall and thus no longer produce electricity. Hence, only spinning at a rate that produces the grids frequency.
Note that I'm talking about older wind generators with no power electronics to control the pitch.
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