EEE223 Energy Conversion II Md. Asif Uddin Khan Lecturer, EEE BRAC University

Power Generation By Wind Turbine Materials taken from: WIND ENERGY SYSTEMS, by Gary L. Johnson, Rainbow Power Company Ltd., Australia; 2004

 Introduction to Wind turbine system  Construction, Wind turbine power  Synchronous and asynchronous operation  Wind turbines coupled with(a)Synchronous (b) DC, (c) Induction generators

 Wind was almost the only source of power for ship until Watt invented the steam engine in the 18 th Century CE (Christian Era).  Denmark was the first country to use the wind for generation of electricity. The Danes were using a 23m diameter wind turbine in 1890 to generate electricity. By 1910, several hundred units with capacities of 5 to 25 kW were in operation in Denmark.  The largest wind turbine built before the late 1970’s was a 1250 KWA machine built on Granpa’s Knob, near Rutland, Vermont in 1941 and named as the Smith-Putnam turbine.

Darrieus Turbine: Vertical axis wind turbine was built by Darrieus in Fig. 5 shows a 17 meter Darrieus turbine built at Sandia. The diameter of the blades is the same as the height, 17 m. The extruded aluminum blades were made by Alcoa ( Aluminum Company of America, Alcoa Center, Pennsylv ania). This machine is rated at 60 kW in a 12.5 m/s wind. The Darrieus has several attractive features. One is that the machine rotates about a vertical axis, hence does not need to be turned into the wind. One disadvantage of the Darrieus is that it is not normally self starting. That is, if the turbine has stopped during a period of low wind speeds, it will not us ually start when the wind speed increases. Starting is usually accomplished by an induction motor connected to the local utility network. However, this is not necessarily a major disadvantage because the same induction motor can be used as an induction generator to supply power to the utility network when the turbine is at operating speed network when the turbine is at operating speed.

How Wind Turbine work?

Power Output from an Ideal Turbine – (Derivation)

Continuation:

Power output from a practical turbine- (Derivation) The coefficient of power of a wind turbine is a measurement of how efficiently the wind turbine converts the energy in the wind into electricity.

Betz Limit: Albert Betz was a German physicist who calculated that no wind turbine could convert more than 59.3% of the kinetic energy of the wind into mechanical energy turning a rotor. This is known as the Betz Limit, and is the theoretical maximum coefficient of power for any wind turbine.

Continuation:

A small wind turbine contains three blades, each 4 meters long. If the turbine rotates at a rate of 72 rpm answer the following questions considering a wind speed of 6 m/s and a wind density of 1 kgm -3. a)Calculate the amount of energy with which the wind is striking the turbine b)Calculate the maximum output power that can be harnessed from wind c)Calculate tip-speed ratio (TSR) d)Actual power output from the wind turbine

Methods of Generating Synchronous Electrical Power:

Asynchronous Electrical System:

There are a number of advantages to synchronized operation (utility connected) in that frequency and voltage controlled by the utility, reactive power for induction generators is available, starting power for Darrieus turbines is available and storage requirements are minimal But in asynchronous operation the main disadvantage is requirement of storage facility and/or back up diesel generators to combat wind power intermittency and unavailability of reactive power in case induction generators are used. For loads requiring fixed frequency, AC ‐ DC ‐ AC system is used in asynchronous operation i.e. if AC generators are used,their output will be converted into DC and then inverted at the desired fixed frequency AC.

DC Shunt Generator in battery Charging Circuit:

Self excited Squirrel Cage Induction Generator