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Lecture 30 November 4, 2013. ECEN 2060 Lecture 30 Fall 2013. Wind Power Systems. 1. Windmills go back a long time. A key money maker for milling grain. 2. First use for electrical generation in 1891 by Poul la Cour used generate hydrogen. 3. Used shortly afterward in the rural US.

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## Lecture 30 November 4, 2013

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**Lecture 30 November 4, 2013**ECEN 2060 Lecture 30 Fall 2013**Wind Power Systems**• 1. Windmills go back a long time. A key money maker for milling grain. • 2. First use for electrical generation in 1891 by Poul la Cour used generate hydrogen. • 3. Used shortly afterward in the rural US. • 4. 1941 Grand Paw’s Knob Vermont 1250 kW,175ft two blade system. Failed in 1945 • 5. 1970’s to mid 1980’s in California and then to Europe**Characteristics of Some Wind Turbines**• 1. Horizontal Axis Wind turbine Up wind and Down wind. • A. Down wind has advantage of self aligning (yaw) • B. Disadvantages Shadowing by tower that increases flexing of the blades which, decrease power, increases fatigue and noise. • C. Up wind Advantage More power, Smoother • D. Disadvantages more complicated control • 2. Vertical Axis, Darrieus • Advantage Heavy equipment on the ground. Lighter tower. • Disadvantage Blades close to the ground where the wind is slower. Low starting torques. Hard to feather in high winds.**Wind Turbines**• Most wind turbines are up wind horizontal. • Many blades high torque and works well at low wind speeds. • Two blades turn faster than 3 blades, less turbulence. 3 blades smoother and installed the most. 3 blade weights more.**Temperature Correction for Air Density**The molecular weight of air is approximately 28.97 and the density at 15o C is 1.225 kg/m3**Table of Air Pressure with Corrections for Temperature and**Altitude. • .**Effects of Tower Height**Z is the roughness length**Effects of Variation of Wind Speed with Height on Stress**This leads to vibrations, noise, blade flexing and fatigue. Factors to 1.45 more power at top to bottom in example.**Maximum Rotor Efficiency**Betz limit 1/3 initial velocity**Blade Efficiency**Assume uniform velocity over the blade To find the maximum power efficiency**Real Turbines**1 Best 80% of Betz limit more often 40% to 50% 2. Depends on ratio of rotor speed to wind speed. Often defined in terms of Tip speed.**Matching Generator Size to Rotor Diameter with Wind Speed**• 1**Blade Speed Limits**• 1. Want to operate in the TSR of 4-6 • 2. Example 40m blades 600kW ,14m/s, This leads to 26 revolutions per minute and tip speed of 56m/s • 3. Required gear ratio to get to 1800rpm of 67.4 • 4. Wind Power of 2,112 kW to get 600kW or an efficiency of 28%**Types of Generators**• 1. Synchronous Generators • A. Fixed Speed • Rotational speed N(rpm) = p = number of poles • f = frequency for a three phase winding. 2. Induction Generators These generators have slip between the rotor speed and the speed of the rotating field in the stator.**Generators for Wind Turbines**• 1. A key issue is the variable of the wind speed and a need for nearly constant speed to achieve 50 or 60hz. • 2. Basic equations • F= q(E + vxB) = qE + I xB and Vinduced = - = - ~ I 3. Note the current I is proportional to the rate of change of the magnetic field B and the force is proportional to the product B ∂B/∂t 3. Synchronous Generators A. Need for constant speed to keep output at 60hz. 4. Induction Generators**Induction Generator**• 1.Fixed windings on the rotor and does not require brushes or electrical contact with the rotor. • 2. The rotor runs a little slower than the rotating field when operating as a motor and faster when it is working as a generator. • 3. The induced current in the rotor conductors generate the magnetic fields that lead to the torques.**Squirrel Cage Rotor**Note 3 phase driving current gives a rotating field when the currents are 120 degrees out of phase Synchronous speed Ns = 120 f/p where f is the frequency and p Is the number of poles.

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