A 350 kVA Windmill at Satara, in the state of Maharashtra, India. A brief description of overall working of Suzlon windmills at this location is given here. The author is thankful to Suzlon for the inputs given during the visit to the site in Nov. 2002

More than 560 windmills have been errected on this plato near Satara. Most of these are of 350 kVA rating. A few are of 1000 kVA. Towers for 350 kVA units are 50 meters in height. 1000 kVA units require towers of 60 meters height. Power is generated at low voltage of 415 volts and is then stepped up by transformers near the base of the tower. These windmills are errected, operated and maintained by Suzlon. These windmills are divided in 5 groups . A monitoring station in the form of a two storied circular shaped building called CMS ( computerized monitoring station ) monitors and controls opertion of the units under it. Monitoring Stations have PCs which monitor parameters like wind speed, wind direction, kW, rotational speed, power generation trend, faults etc. Around 100 different faults are monitored. Some faults are of “Auto Reset” type. e.g. windspeed falling below 3.5 m/sec is a fault which gets cleared automatically if the windspeed increases again. DATA logged is sent to Suzlon’s office in Pune via VSAT everyday. The data is analysed here and forwarded to the respective investors. Details of a 350 kVA windmill: Blades of windmills are made of FRP in the factory of Suzlon at Daman. These blades are hollow. Each blade is 15.5 meters in length for 350 kVA unit and 27 meters for 1000 kVA unit. The tips of the blades are rotatable and are rotated by mechanism inside the blade, when the windmill is to be stopped. There are wind speed sensors which monitor the maximum speed allowed. If the speed is more than 7 m/sec, the tips of the blades are turned so that the winmill stops rotating. Wind sensors keep watch on the direction of the wind. An average direction is determined after monitoring the data for 30 minutes. There are motors which are called Yaw motors which turn the blades against the direction of wind for maximum power output. Hydraulic pressure of 80 bars is used to hold the blades in that direction later on. Blades are allowed to turn by a maximum of 720 degrees, i.e. two full rotations. If the need arises to turn further the Yaw motors reset themselves to zero degree again. Three cables of 120 sqmm cross sectional area are brought down from the generator at the top. This generator is driven by the blades through a gear box having a ratio of 1:32. This means that blades rotate at 24 rpm when the genrator is rotating at 750 rpm. How windmill starts generating: As the speed of the wind slowly rises and brings the speed of the generator near 750 rpm, a thyristorised drive unit becomes on and feeds power available in the grid to the generator making it act like a motor for 2 to3 seconds. This brings the speed of the generator to 750 rpm. Once the generated voltage is synchronised with the grid voltage, the thyristor drive goes off the grid and generator starts feeding the power to the grid. If the wind speed goes above 7 m/sec then the generator configuration is changed to “6 poles” from “8 poles”, making it a 1000 rpm generator. How is a location selected ? Selecting a windy plato is not enough for choosing an exact location. 5 towers, 50 m tall, are erected and data of wind speed, direction etc is collected for two years. Analysis of this data helps in choosing one best location out of the 5 locations.