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Feature | September 2011

Among the clouds

The 210 MW Vankusawade wind farm in Satara, Maharashtra, is situated about 1,150 metres above sea level. R Srinivasan returns with a heady feeling about wind energy, partly due to the altitude.

About 350 km away from Mumbai, Suzlon operates, what was at the time of its construction Asia's largest wind park, the 210 MW Vankusawade wind farm in Satara, Maharashtra. As our vehicle trundled uphill through deep red soil pockmarked in some places with watery puddles and began approaching the company's knowledge centre, the gentle humming sound from the lazily turning blades of the windmills became more audible. On one of the lattice wind mills, the blades were stationary and the blade tip had been turned to indicate that it was 'stalled' for maintenance and aerodynamic braking purposes.

Vankusawade wind farm

The around 30 km long and 4 km wide wind farm has a total installed capacity of around 210 MW and there are totally 571 turbines (of 350 kW, 600 kW, 1 MW and 1.25 MW capacities) here. It is said that their lifespan is around 20 years and that their productivity differs from model-to-model and site-to-site. This site is considered ideal because of its north-south location since the turbine can take advantage of the wind flow. Also the presence of the Koyna dam and the Arabian Sea (about 60 k away) cause temperatures variations whereby hot air is replaced by cooler winds in a constant cycle.

The company's recently-launched prototype S9X suite of turbines has been installed at the Jaisalmer wind farm site. After a look around the scenic wind farm, we headed for the knowledge centre.

Knowledge Centre

New trainees to the company, during the basic technical induction programme, are taught about the history of wind power, essentials of wind power, types of wind mills, latest technologies, how a wind turbine generator (WTG) works and how they can be operated to ensure optimum performance and other such details.

Although eight states with wind farms have their own centres, the USP of this one is the presence of a fully-functional 1.25 MW simulator turbine and a 1.5 MW one that is being readied for the purpose. The 1.25 MW true-to-life model of the turbine, or simulator, goes beyond traditional classroom sessions and shows the actual functioning of a turbine. The 1.25 MW simulator gives a person an idea of the various components inside a nacelle and their functioning and in this manner supplements the theoretical information gained by engineers during the classroom sessions. There is also a model to exhibit how turbines can be monitored using supervisory control and data acquisition (SCADA) systems. The actual SCADA systems are used to monitor the state of windmills. For e.g.: Anomalies due to heavy rain can be detected by these systems. Incidentally, the SCADA system at Pune monitors all the turbines in India.

On the way back at around 3 pm, the thick mist came floating in towards the vehicle and it became bone-chillingly cold. As our vehicle wound its way downhill, quite a few tourist buses were headed towards the wind farm. It gave rise to a reassuring thought that such technology centres can be used to not only create better engineers with hands-on experience, but also to create greater awareness among the masses about the benefits of wind energy.

Windmill fundas
  • Some of the stages in setting up a wind farm: Before setting up the turbines, the wind resource department conducts studies for over one-and-a-half years to test wind resources and average wind speeds. The wind speed should ideally be from a minimum of 3.5 metres per second to a maximum of around 25 metres per second. This is dependent on the type of turbine, so a 2.1 MW turbine can operate at a maximum speed of around 25 metres per second. Then in the projects phase it is decided as to how many turbines have to be set up for a particular client and of what capacity and then there is the land procurement process. The turbines are then commissioned and handed over to the operations, maintenance and services (OMS) department.
  • Windmills operate at maximum capacity from mid-May to September. The slow months in terms of wind generation are from January to April-May due to low wind speed and very high temperature.
  • To tackle intermittent wind energy issues and heavy gusts of wind (akin to voltage fluctuations or power spikes), the fluid coupling in the nacelle control slip and absorb gusts and balance the revolutions per minute (RPM) discrepancies between the rotor and generator.
  • With a constant wind speed of over 12 to 17 metres per second for an hour, a 2.1 MW turbine will produce optimum energy of 2.1 MW per hour.
  • The optimum rotor speed of a (350 kW) turbine would be around 23 revolutions per minute.
  • The state's installed capacity of wind power is 1,700 MW and in Sangli and Satara about 700 MW of wind power is generated. On a rough estimate, 1 MW can light up nearly 800 homes.
  • Sometimes at speeds below 3.5 metres per second, the turbine may be working, the grid and system may be okay, but it may not produce energy and the output may be zero. Once the wind speed goes above 3.5 metres per second, the turbine will start producing energy. The average productivity of wind farms also depends on wind speeds and the location, apart from other factors. For e.g.: the Sankaneri wind farm in Tamil Nadu, which hosts over 650 MW of installed capacity, is blessed with one of the best wind power potential. Thanks to its unique topography that exposes it to two monsoon seasons in a year, the windy season extends over a longer period.
  • Turbine maintenance is usually done on a quarterly basis and annual maintenance has to be done before the high winds start from June.
  • If there is a problem with the cable, gearbox, generator etc, the machine's problem has to be rectified within a prescribed schedule (minimum 8 hours) and even the most severe of cases has to be resolved, at the latest, within 48 hours. But due to safety reasons, the maintenance crew can enter the hub only at speeds below 10 metres per second.
  • Around 12 persons may be involved in maintenance and the nacelle itself can accommodate around 4-5 persons.
  • There are around 250 employees at Vankusawade and the daily schedule of maintenance personnel, with three shifts, begins from 8 am till around 6.30 pm.
  • In terms of lightning protection, at the end of the blade, there is a unit which senses lightning and then sends signal to the hub, nacelle and then to the ground. There may be around 8 - 10 earthing pits on the ground (for the transformer, tower etc) near the switchyard which houses the transformer. The purpose of 300 volt batteries is that they constantly provide energy, protect the WTG and also stop the blades in a precise manner.
  • The height of (say a 350 kW) tower varies from around 150 feet to around 180 feet. The preferred material for towers is steel and the blades are made of composite material.
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