INDUCTION GENERATOR FOR WIND POWER GENERATION OUTLINES INTRODUCTION HISTORY WIND TURBINES TERMINOLOGIES USED WORKING CONTROLLING ADVANTAGES OF VARIABLE SPEED GENERATION WHY INDUCTION GENERATOR? ADVANTAGES & DISADVANTAGES OF WIND ENERGY APPLICATIONS CONCLUSION INTRODUCTION Wind turbines convert the kinetic energy present in the wind into mechanical energy by means of producing torque. Large scale wind power projects are an attractive alternative to conventional capacity expansion. In the present scenario , most wind turbine manufacturers now equip power generating units by induction generators. They are operated either at fixed speed or variable speed. Generators driven by fixed speed turbines can directly be connected to grid. Variable speed generators need a power electronic converter interface for interconnection with the grid. Variable speed generation is preferred over fixed speed generation. HISTORY In 200 B.C., in ancient Persia , the earliest windmills were used to grind grain. These early devices consisted of one or more vertically-mounted wooden beams , on the bottom of which was a grindstone, attached to a rotating shaft that turned with the wind. Starting in the 11th century A.D. , European crusaders brought the concept and developed the DUTCH type wind mill. The first automatically operating wind turbine for electricity generation. It was built by Charles F. Brush in 1887-1888 in his backyard. Charles’s 60 foot , 80,000 pounds turbine supplied 12 kW power to 350 incandescent lights. Its rotor was 17 meters in diameter. WIND TURBINES Wind turbines convert wind energy to electricity for distribution. Aerodynamic modeling is used to determine the optimum tower height, control systems, number of blades and blade shape. Wind turbines are generally classified depending on their axis of rotation as: -Horizontal axis type, -Vertical axis type. The horizontal axis types generally have better performance. A quantitative measure of the wind power available at any location is called Wind Power Density(WPD). Commercial wind farms generally produce a WPD of 400 watts/square meter. HORIZONTAL AXIS WIND TURBINE VERTICAL AXIS WIND TURBINE AALBORG-TURBINE DARRIEUS-WINDMILL The ROTOR component : Its approx 20% of the wind turbine cost, includes the blade for converting wind energy to low . speed rotational energy. The GENERATOR component : Its approx 34% of the wind turbine cost, includes electrical generator ,the control electronics and a gearbox. . The STRUCTURAL component : Its approx 15% of the wind turbine cost, includes the tower and yaw mechanism. TERMINOLOGIES USED ANEMOMETER: IT’S A WIND DIRECTION SENSOR WITH DIGITAL DISPLAY. USED IN AREAS WHERE AC POWER IS NOT AVAILABLE. MONITORS WIND SPEED AND STORE MAX AND AVERAGE VALUE. YAW SYSTEM: THEY PERFORM THE TASK OF ORIENTING THE ROTOR IN THE DIRECTION OF WIND. NACELLE: IT IS STRUCTURE THAT HOUSES ALL OF THE GENERATING COMPONENTS LIKE-GEARBOX, ROTOR SHAFT AND BRAKE ASSEMBLY ETC. ROTOR BLADES: THE BLADES ARE THE SAILS OF THE SYSTEM , WHEN THE WIND FORCES THE BLADES TO MOVE , IT HAS TRANSFERRED SOME OF ITS ENERGY TO THE ROTOR. . SHAFT SYSTEM: THE WIND TURBINE SHAFT IS CONNECTED TO THE CENTRE OF THE ROTOR , WHEN THE ROTOR SPINS THE SHAFT SPINS AS WELL.THUS ROTOR TRANSFERS ITS MECHANICAL ROTATIONAL ENERGY TO THE SHAFT. WIND VANE: SMALL TURBINES ARE POINTED INTO THE WIND BY USING IT. GEAR BOX: IT TURNS THE SLOW ROTATION OF THE BLADES INTO A QUICKER ROTATION THAT IS MORE SUITABLE TO DRIVE AN ELECTRICAL GENERATOR WORKING Aeroturbines convert wind energy into rotary mechanical energy. A mechanical interface , consisting of a step –up gear and a suitable coupling transmits the energy to an electrical generator. The output of this generator is connected to the load or system grid. The controller senses the wind direction ,wind speed , power output of the generator and other necessary performance quantities of the system and initiates appropriate control signals to take suitable corrective actions. Several schemes for electrical generation have been developed. These schemes can be broadly classified under these categories: 1. Constant speed generation system. 2. Variable speed generation system. As constant speed generation system suffer from a number of drawbacks hence variable generation system is preferred . GEARING WIND AND ELECTRICAL TURBINE COUPLING GENERATOR WIND WT WT GC EG TO LOAD UTILITY GRID CONTROL GEN. PITCH YAW SIGNAL TEMP. CONTROL CONTROL SPEED CONTROLLER COMPONENTS OF WIND ELECTRIC SYSTEM VARIABLE SPEED WIND ENERGY CONVERSION SYSTEM In variable speed systems, the turbines rotor absorbs the mechanical power fluctuations by changing its speed. So the output power curve is smoother which greatly enhances the quality of power. However ,since variable speed operation produces a variable frequency voltage, a power electronic converter must be used to connect to the constant frequency grid It can be achieved by using: WECS with Squirrel cage induction generator. WECS with Wound rotor induction generator. WECS with Doubly-fed induction generator. WECS with Squirrel cage induction generator In this set up the stator of the squirrel cage induction generator will be connected to the grid by the means of back to back connected power electronic converter bridges. Since the power converter has to convert all the stator power, the converter size depends on the stator power rating. ADVANTAGE: Ability to make the best use of available wind power. It eliminates the need for a capacitor bank. DISADVANTAGE: Cost of power converter is high. WECS with Wound rotor induction generator The power converter size in the earlier system can be reduced by using it on the rotor side of a wound rotor induction generator. Above fig shows a variable speed system using a wound rotor generator. The power converter is now connected between the rotor and grid , so it needs to carry only the slip power. ADVANTAGES: For utility scale wind power generation it outweighs squirrel cage machine. WECS with DFIG Double-fed induction machines can be operated as a generator as well as a motor in both sub-synchronous and super-synchronous speeds, thus giving four possible operating modes. Only the two generating modes at sub-synchronous and super-synchronous speeds are of interest for wind power generation. BACK TO BACK CONNECTED POWER CONVERTER BRIDGES Two power converter bridges connected back-to-back by means of a dc link can accommodate the bidirectional rotor power flow in a DFIG. The purpose of the grid side converter is to maintain the dc link voltage constant. It has control over the active and reactive power transfer between the rotor and the grid. The rotor side converter is responsible for control of the flux, and thus, the stator active and reactive powers . ADVANTAGES: Less cost of AC-AC converter. Improved system efficiency. WIND POWER DEVELOPED BY THE WIND TURBINE IS GIVEN BY : P=(Cp AρV^3)/2 Where Cp: Power coefficient A: Area swept by rotor blades ρ: Air density V: Velocity of wind CONTROLLING Induction generator control: Cage rotor induction generators can be made to operate over a wider speed range by pole changing or pole amplitude modulating the main winding. A Wound rotor induction generator can be controlled by varying the slip energy of the rotor circuit using following methods : rotor resistance control , cascading etc A bank of capacitors connected to the terminals can be used. Transmission control: By using silicon controlled rectifier device. Conduction period of electronic devices can be controlled by applying delayed trigger pulses. Load control: Using switched load resistors stepwise load approximation can be made . Operation within the maximum current loading of the generator can be set. ADVANTAGES OF USING VARIABLE SPEED GENERATION Better energy capture than fixed speed generation. Mechanical stress reduction of turbine. Acoustic noise reduction. Cost effective and entirely feasible. WHY INDUCTION GENERATOR? Simple and robust construction. Can run independently. Inexpensive. Minimal maintenance. Inherent overload protection. At high speed, reduces size and weight of machine(roughly 0.33m long, 0.5m diameter) and filter components. Wind turbine data The wind turbine is a MOD 5 type with the following data Nominal values Turbine 1.8 MVA Rated wind speed 7 m/s Rotor radius 40 m Rotor swept area 5026.548 m2 Air density 1.225 kg/m3 Gear box efficiency 0.979 pu Gear ratio (machine/turbine) 120 ADVANTAGES OF WIND ENERGY It is a renewable source of energy. Wind power systems are non-polluting. Wind energy systems avoid fuel provision and transport. On a small scale upto a few kilowatt system is less costly. DISADVANTAGES OF WIND ENERGY Wind energy available is fluctuating in nature. Wind energy needs storage capacity because of its irregularities. Wind energy systems are noisy in operation. Windpower systems have a relatively high overall weight. APPLICATIONS OF WIND ENERGY Invarious industrial process like: food processing, textile processing , production of inorganic chemicals like chlorine, bromine etc Wind powered pump can be used to desalinate water. powerful turbines(50kW), are for operating irrigation The pumps , navigational signals and remote communication. Inaqueduct system , large scale wind driven units can provide power for the pumping of water from the main reservoir to auxiliary reservoir. CONCLUSION Wind is one of the most flexible and tractable of all energy sources, since the mechanical energy derived directly from the wind can be readily and efficiently converted to other forms of energy. The cost of power generation from wind farms has now become lower than diesel power and comparable to thermal power in several areas of our country especially near the coasts. Thus Wind power can be used in centralized utility applications to drive synchronous AC electrical generators.
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