Wind turbines technology in India and Maximum Power Extraction...

Wind turbines technology in India and Maximum Power Extraction...:

The Renewable Industry in India starting from early 1990’s was focused on the wind turbine segment mainly because of proven life time for wind mills which had more than 20+ years of running life at the wind farms. All major structural components also proved in accordance with design specified by IEC or GL guidelines in US and Europe.

India took a lead in turbine development with the support of government subsidies & bank loans availing warranty up to 5 years, operation & maintenance support for 5 to 20 years by manufacturers. Above all the tariff paid for electrical power in each state was also very attractive to get returns on investment within a period of 6 to 7 years. Wind mill owners either sold power to government grid or few others used it as their own captive power for their Industries. All the factors helped investors to confidently get into the wind turbine segment as best renewable option. Later by 2010 the entry of solar power began due to vast land availability and cost reduction of module due to change of production cost. Imports stopped from US, Germany and moved to Chinese suppliers which helped Solar power becoming more cheaper and popular, above all it was also high tariff of Rs 7/unit announced by the government of India in early 2010 and low cost of land for solar farms. Solar farms majorly had an advantage of using any location to extract solar energy, unlike wind turbines which needed high wind potential site locations. Land available for high wind slowly got exhausted. After solar entry in large scale projects the wind turbine industry faced lot of challenges in making turbines cost effective. Increase in megawatt was very important; it was possible by increasing hub height of tower which helped to get more wind speeds. Also an increase in the rotor diameter helped to get more energy captured from wind.

Technological change, Cost reduction & energy yield strategies for the wind turbine segment - Wind designers looked at the possibility to use Lattice & Tubular- Hybrid model of design instead of tall tubular towers to reduce cost of steel used in tower. Height increase was from most commonly used 90 meters to 120 meters i.e increase by 30 meters which enables to get higher wind speeds, increases yield and optimizes cost of tower due to lattice design. Today turbines are planned up to 150 meters hub heights.

Wind turbine megawatts were increased beyond 2+ Megawatts along with longer blades which helped to extract more energy from class III low wind sites, this worked as a major advantage.

Wind turbines are designed based on IEC or GL standards which consider a standard air density of 1.225kg/m3. Some turbines are S design made considering specific density. Wind speeds are set for specific location which can easily bring down the cost of turbine due to reduced load on blades, tower & foundation etc.

Designed turbines usually have a residual life time of more than 20 years which can be estimated using fatigue calculations of each component in the turbine. It would save cost of turbines if the main structure along with sub-components is designed exactly for 20 years and hence, it helps to design light weight, optimum design and reduces the mass of turbine with cost reduction.

Efficiency improvement for a WTG on Mechanical side started way back in 2003 when fluid couplings were used commonly to connect high speed generators & high speed shaft. It soon got obsolete soon and succeeded by steel plate coupling. To avoid oil churning losses of Impeller in fluid coupling which was leading to huge loss in energy efficiency variable speed generator was introduced. It was further improved to DFIG & later to Direct Drive with self-excited Permanent Magnet design. It increased the efficiency up to 98% from wind turbines.

Modular design of Gear box & Generator were coupled together and connected to the Rotor Hub with a shorter length of main shaft. This helps in direct torque transmission to sun wheel and also reduces drive-train losses and bending loads. It also helped in cost reduction on alloy steel shafts totally eliminating the main bearing & compact design helped in easy transportation.

Blade development has come a long way mainly because it has a better surface profile to receive wind. The length varies between 27 m to 65 m, this longer length & profile helps to extract maximum energy yield from class III or class IV low wind sites which are presently available across India. Another major factor in Blade length depends on the countries road infra-structure and transport vehicle movement. To handle longer blades of 65 meters as turning radius would need latest telescope trucks which are expensive.

Today all design advancements are made on modern wind turbines both in mechanical and electrical aspects. Since it is all energy from wind, we need to look at the wind speed which goes rapidly up down and also the direction of wind coming from all 360 degree directions. Hence, we suggest with micro level detail study and smart tweaking that there still lies a possibility for energy yield to be increased.

Today there is a significant drop in cost per unit paid for wind which is equal to solar energy. After reverse auction bidding started in early 2017, it is now time to think about two options. One would be to make in India for most components and certify them as alternate vendor sources available. Next would be to look into the possible micro level details of technical due – diligence of wind turbine to help Increase the energy yield. Few suggestion are given below:-

1) Exact micro sighting GPS location of turbine installed.

2) Generator cooling system performance improvement

3) Main Gear box tooth backlash status.

4) Gear oil check contamination level which creates churning losses.

5) Pitch zero correction & Yaw misalignment correction.

6) Anemometer accuracy.

7) Blade rotor imbalance correction

8) Thermography check at cable connection at Junction box.

9) Blade surface dust sediments or any damages

10) Possible way for including vortex generator on blades.

11) Frequency Convertor cooling system on/off time based day & night settings to reduce losses.

12) Power curve verification of new turbines to find any mechanical issues.

13) Cut in & Cut out wind speed.

14) Optimum pitch angle to get maximum Cp value of blade.

15) Campbell diagram check for 1 pole and 3 pole excitation for natural frequency range.

16) Optimum mode gain setting values

17) Noise, Vibration , Wake effects & RPM of turbines.

18) Energy yield theoretical calculated vs actual yield comparison.

19) Yard transformer oil levels.

20) Cable transmission losses.

21) Cable line distance from turbine to substation.

22) Rotor hub angular misalignment

23) Noise & vibration measurement checking

24) Load measurement of turbine.

25) Data analytics of the turbine.

26) Power quality measurement.

27) Earthing connection status.

28) Met mast and turbine parameter comparison.

29) Temperature of main bearing grease color and availability of grease around bearing.

We as TUV India (TUV Nord Group) have the expertise & Ideas to support any company in improving their efficiency to get the optimum output from their wind and solar farms.

About The Author

Rajarethinam RavindranDeputy General Manager - Technical, Renewable
TUV India Pvt Ltd