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 Grand Paw’s Knob Vermont 1250 kW,175ft two blade system. Failed in ’s to mid 1980’s in California and then to Europe 2 ECEN2060

Rapid Grow of Wind Capacity 3 ECEN2060

World Wide Growth of Wind Energy 4 ECEN2060

Fraction of Total Generation by Wind 5 ECEN2060

Data on Wind 6 ECEN2060

Types of Wind Turbines 7 ECEN2060

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

Schematic for Horizontal Wind 9 ECEN2060

Wind Turbine Gear Box 10 ECEN2060

Area of Capture 11 ECEN2060

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

Pitch Angle Controls Lift, Speed and Power 13 ECEN2060

High Pitch Can Lead to Stall 14 ECEN2060

Wind is Slowed by Blades 1 15 ECEN2060

Wind Power 16 ECEN2060

Wind Power 17 ECEN2060

Area of Darrieus 18 ECEN2060

Lecture 31 November 6, ECEN2060

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

Dry Air Pressure at 1Atmosphere 21 ECEN2060

Altitude Correction 22 ECEN2060

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

Effects of Tower Height 24 ECEN2060 Z is the roughness length

Surface Friction 25 ECEN2060

Roughness 26 ECEN2060

Effects of Height with Different Roughness 27 ECEN2060

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.

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

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

Real Turbines 31 ECEN 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.

Blade Efficiency 32 ECEN2060

Efficiency for Different Blade Systems 33 ECEN2060

Idealized Operating Power Curve 34 ECEN2060

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

Blade Speed Limits 1. Want to operate in the TSR of 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 Wind Power of 2,112 kW to get 600kW or an efficiency of 28% 36 ECEN2060

Some Real Turbines 1 37 ECEN2060

Efficiency and Power for Some Turbines 38 ECEN2060

Average Wind Speed Classifications 39 ECEN2060

Wind Speed Measurements 40 ECEN2060

Types of Generators 41 ECEN2060

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

Types of Systems 43 ECEN2060

Synchronous Generator 44 ECEN2060

A Direct Drive Permeate Magnetic Machine 1 45 ECEN2060

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

Forces with a Rotating Magnetic Field 47 ECEN2060

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.

Squirrel Cage Rotor 49 ECEN2060

Rotating Magnetic Fields 50 ECEN2060

Induction Motor Torque –Slip Curve 51 ECEN2060

Example of Induction Motor. 52 ECEN2060

Inductance Machine as Generator 53 ECEN 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

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

Inductance Generator Speed Control 55 ECEN2060

Examples of Speed Adjustments. 56 ECEN2060

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

Variable Speed Turbine and Indirect Connection to the Grid 58 ECEN2060

Doubly Wound Induction Machine 59 ECEN2060

Gearless Drive 1 60 ECEN2060

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

A wind speed histogram 62 ECEN2060

A Probability Density Function 63 ECEN2060

Weibull and Rayleigh Functions 64 ECEN2060

Weibull Density Functions 65 ECEN2060

The Rayleigh Probability Density Function 66 ECEN2060

Rayleigh Distribution 67 ECEN2060

Some Real Data 68 ECEN2060

Midwest Wind 69 ECEN2060

70 ECEN2060

71 ECEN2060

Wind Turbine Gear Box 72 ECEN2060

73 ECEN2060