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Lecture 30 November 4, 2013 ECEN 2060 Lecture 30 Fall 2013

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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 2 ECEN2060

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Rapid Grow of Wind Capacity 3 ECEN2060

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World Wide Growth of Wind Energy 4 ECEN2060

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Fraction of Total Generation by Wind 5 ECEN2060

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Data on Wind 6 ECEN2060

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Types of Wind Turbines 7 ECEN2060

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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. 8 ECEN2060

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Schematic for Horizontal Wind 9 ECEN2060

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Wind Turbine Gear Box 10 ECEN2060

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Area of Capture 11 ECEN2060

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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. 12 ECEN2060

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Pitch Angle Controls Lift, Speed and Power 13 ECEN2060

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High Pitch Can Lead to Stall 14 ECEN2060

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Wind is Slowed by Blades 1 15 ECEN2060

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Wind Power 16 ECEN2060

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Wind Power 17 ECEN2060

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Area of Darrieus 18 ECEN2060

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Lecture 31 November 6, 2013 19 ECEN2060

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Temperature Correction for Air Density 20 ECEN2060 The molecular weight of air is approximately 28.97 and the density at 15 o C is 1.225 kg/m 3

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Dry Air Pressure at 1Atmosphere 21 ECEN2060

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Altitude Correction 22 ECEN2060

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Table of Air Pressure with Corrections for Temperature and Altitude.. 23 ECEN2060

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Effects of Tower Height 24 ECEN2060 Z is the roughness length

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Surface Friction 25 ECEN2060

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Roughness 26 ECEN2060

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Effects of Height with Different Roughness 27 ECEN2060

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Effects of Variation of Wind Speed with Height on Stress 28 ECEN2060 This leads to vibrations, noise, blade flexing and fatigue. Factors to 1.45 more power at top to bottom in example.

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Maximum Rotor Efficiency 29 ECEN2060 Betz limit 1/3 initial velocity

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Blade Efficiency 30 ECEN2060 Assume uniform velocity over the blade To find the maximum power efficiency

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Real Turbines 31 ECEN2060 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.

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Blade Efficiency 32 ECEN2060

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Efficiency for Different Blade Systems 33 ECEN2060

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Idealized Operating Power Curve 34 ECEN2060

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Matching Generator Size to Rotor Diameter with Wind Speed 1 35 ECEN2060

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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% 36 ECEN2060

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Some Real Turbines 1 37 ECEN2060

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Efficiency and Power for Some Turbines 38 ECEN2060

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Average Wind Speed Classifications 39 ECEN2060

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Wind Speed Measurements 40 ECEN2060

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Types of Generators 41 ECEN2060

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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 V induced = - = - ~ 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 42 ECEN2060

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Types of Systems 43 ECEN2060

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Synchronous Generator 44 ECEN2060

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A Direct Drive Permeate Magnetic Machine 1 45 ECEN2060

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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. 46 ECEN2060

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Forces with a Rotating Magnetic Field 47 ECEN2060

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Squirrel Cage Rotor 48 ECEN2060 Note 3 phase driving current gives a rotating field when the currents are 120 degrees out of phase Synchronous speed N s = 120 f/p where f is the frequency and p Is the number of poles.

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Squirrel Cage Rotor 49 ECEN2060

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Rotating Magnetic Fields 50 ECEN2060

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Induction Motor Torque –Slip Curve 51 ECEN2060

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Example of Induction Motor. 52 ECEN2060

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Inductance Machine as Generator 53 ECEN2060 1.The wind starts the machine as a motor until it gets above synchronous speed 2.Can be connected to the grid or self excited with a capacitor and remnant magnetic field. Set it to resonate with the Stator Inductance

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Need for Speed Control 1. Want to operate with a tip speed ratio of 4-6 for maximum power and blade efficiency C p 2. If direct connection to the grid need a fixed blade speed for phase and frequency control to match frequency on the grid if you have a fixed turbine to generator connection. 3. Need to shed power in high winds. 4. Use a gear box. 5. Use pitch control of the blades 6. Control of slip which in turn controls power. 7. Doubly wound rotor. 54 ECEN2060

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Inductance Generator Speed Control 55 ECEN2060

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Examples of Speed Adjustments. 56 ECEN2060

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Control of the Number of Poles in the Stator 1. This can be done by changing the connections on the windings. For example two poles adjacent to each other can be connected to look like one. This is 1/2 the frequency for a fixed speed. 2. Change gear ratio. 3. Varying the resistance seen by the rotor winding varies the slip. 4. Use an indirect connection to the grid by way of an inverter AC to DC to AC(60hz.) This allows for variable frequency into the inverter and variable turbine speed. 57 ECEN2060

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Variable Speed Turbine and Indirect Connection to the Grid 58 ECEN2060

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Doubly Wound Induction Machine 59 ECEN2060

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Gearless Drive 1 60 ECEN2060

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Average Wind Power 61 ECEN2060 This is the wind turbine owners get paid. Note there is a big difference between V average and V 3 average

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A wind speed histogram 62 ECEN2060

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A Probability Density Function 63 ECEN2060

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Weibull and Rayleigh Functions 64 ECEN2060

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Weibull Density Functions 65 ECEN2060

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The Rayleigh Probability Density Function 66 ECEN2060

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Rayleigh Distribution 67 ECEN2060

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Some Real Data 68 ECEN2060

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Midwest Wind 69 ECEN2060

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Wind Turbine Gear Box 72 ECEN2060

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73 ECEN2060

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