April 2012 ~ Goshan's Stream

Wind Farms in Sri Lanka - SEGUWANTIVU AND VIDATAMUNAI WIND POWER PLANTS

Energy is very famous topic in the world. The ways of energy generation and cost is making many governments busy because under current rising energy crisis is making people uncomfortable in their day to day life. These effects are not only in developing countries but also in industrialized developed countries. In industrialized countries, people are using much power to be run the machinery. Both developed and developing countries are using electricity for day to day life of people. For those cases various energy sources are used. Coal power, gasoline, diesel, natural gasses, bio mass, nuclear power and etc can be mentioned as examples. But these sources are in the risk of ending, because they are stored in the earth in limited amount. And they have made many social problems, environmental problems. Some countries are directly refusing some resources like nuclear energy. And they emit large amount of green house gases like N₂O, CO₂, HC, etc to the environment with heat as waste energy. Therefore those sources are reasonable for green house effect. That means it changes the thermal balance of the atmosphere. That means the atmosphere become stable again at higher temperature making huge effect of bio diversity on the earth. And it makes considerable environmental pollution and health pollution directly when all of fossil fuels are being burnt.

Because of above reasons and others, currently world is talking about clean green energy sources. We can be mentioned three type of clean green energy sources. They are Wind, Sea Waves and solar radiation. Wind and sea waves are also indirect forms of solar energy. We can call them as clean green energy sources because we can extract energy from those sources without having any green house or other toxic gas as by product. And the heat wastage during the energy extraction and consumption is not making help to the green house effect. If it is further explained; we know that any energy type is end up as heat. That means it is wasting in to the environment as heat. The wind and sea energy also end up with heat weather we use it or not. It does not make any sense to the average temperature of the earth. When we extract energy from those sources, we make it end up in our way. However final form is heat. It is the same thing that naturally happened.

Most of countries are currently using this energy and trying to do it in more efficient and economical way. More industrialized countries are trying to use sea waves for power generation. But it is more cost effective. But solar and wind power are famous in all countries. It is easy to generate electricity from these sources. Wind energy extraction was very famous for water pumping and running mills. And it makes attraction to the land, but currently wind power is mostly used to generate electricity. Solar power is used to generate electricity or heat. It is also more interesting section in the energy field. These energy sources are freeing forever, renewable and clean & green. They will not make unstable the biodiversity on the earth at the rate of fossil fuel is doing.

GREEN ENERGY EXTRACTION IN SRI LANKA

Sri Lanka is also trying to extract energy from solar and wind. There is one solar farm to generate electricity in Hambntota district. And there are four main wind farms installed in Hambantota district and Puttalam District. The first wind farm is installed in Hambantota as pilot project in 1999 by Ceylon Electricity Board (CEB). It is a 3MW plant with five wind turbines. And there are three 10MW plants in Puththalam District. They are Seguwantivu Wind Power Plant and Vidatamunai Wind Power Plant and Senok wind power plant.

SEGUWANTIVU AND VIDATAMUNAI WIND POWER PLANTS

Seguwantivu Wind Power Plant and Vidatamunai Wind Power Plant are owned by one private company and those are working with CEB as Seguwantivu wind power (Pvt) Ltd and Vidatamunai wind power (Pvt) Ltd. Both of them are supplying 20MW to the national grid. Although the Humbantota wind farm is not 100 percent successful, these wind farms are saying a successful story since their installation.

In Sri Lanka there are considerable potential of hydro power. But it is not sufficient to face annual power requirements and some water shortages. Therefore government and CEB have started to increase the electricity generation from Coal and diesel. According to the CEB reports they are expected to fulfill energy requirement by installing more coal power plants in the future, but we know that it will make many social and environmental problem. Fortunately the Sri Lanka government has a target of produce 10 percent of electricity from renewable energy sources. These wind power plants are as results of that target.

SITE SELECTION FOR SEGUWANTIVU AND VIDATAMUNAI WIND POWER PLANTS

It is important to select suitable site for the wind farm. And there are main considerations; like wind potential during a year, flat surface, low surface roughness, low or less obstacles etc. Sri Lanka government had launched several programs to collect wind data in the island. Those data have used to select the feasibility for the site. Following are the data analyzed to be selected the site;

Ø Wind measurement data of CEB of year 2000/2001

Ø Wind Study done by U. S. National Energy Laboratory in year 2003

Ø Wind Measurements taken by Sustainable Energy Authority at Mullipuram, since March 2007.

Ø Satellite data obtained by Gamesa from March’2002 to March 2007.

According to those data the total wind power potential in Sri Lanka is 20740MW. And most of area is belong to land. And also according to those data puttalam, Mannar, Jafna and some southern areas have considerable wind potential.

When we consider the wind speed in the selected area, it is in favorable range. According to the wind turbine installed in the puttalam, those require wind in the range of 4 – 25 ms^-1. That means too slow and too high wind speeds are not favorable. And also Puttalam district is receiving wind in large period of the year. We know that in Sri Lanka, there are two active monsoons. They are South - West monsoon and North – East monsoon. Puththalam District is covered by the wind of both these monsoons.

And we consider the surface roughness in the site, it is very law. There are no cultivations and buildings close to the site. And it is a coastal area. That gives huge advantage to the site, because there are no any obstacles to the flow of wind from the sea side. That means it is possible to have laminar flow from the wind. For horizontal axis wind turbines laminar flow of wind is required to have maximum performances.

And it is easy transport part to the site. Although there are other areas in Sri Lanka which have good wind potential, they do not have other factors like flat areas, low surface roughness, and transport and grid facilities. Therefore the Mullipuram area where Seguwantivu and Vidatamunai wind power plants is placed are very much suitable.

And also it is important to consider about financial and funding facilities and technical availability.

SELECTION OF WIND TURBINE

And also it is important to select the most suitable turbine and power converter units to be installed in the site. We know there are main two types of wind turbines they are Vertical Axis Wind (VAWT) Turbines and Horizontal Axis Wind Turbines (HAWT). We know VAWT are less efficient than HAWT. And also the most famous HAWT is the three blade type, because engineers have found that that is the most efficient wind turbine type.

There are many wind turbine manufactures in the world. Before buy turbines, Seguwantivu wind power (Pvt) Ltd and Vidatamunai wind power (Pvt) Ltd have done a study on those manufactures. And they have specially considered about wind turbine designers Gamesa, Vestas and suzlon. Finally they have selected the supplier as Gamesa which is a Spain company. The selected model is AE59.

It is recognized that this turbine yields best energy from wind and have preferable power generation of 800MW. And it has less risk on revenue on WT failure. And also this wind tuubine and its system 100% compatible with Sri Lanka grid connection.

It is possible to summarize important feature of AE-59 WIND TURBINE as follows;

CLASS 3 (61400-1)

· Average wind speed from 6-7.5m/s

FULL RANGE VARIABLE SPEED

· High Performance at low winds

SYNCHRONOUS GENERATOR

· Brushless generator

VARIABLE PITCH SYSTEM

· Independent pitch control for each blade

· Hydraulic system

FULL CONVERTER GRID CONNECTION

· Grid connection facilities (P-Q control, voltage dips, etc.)

GL’03 CERTIFICATION IN PROCESS

Part of mechanical system

And this wind turbine is 60m height and the diameter of the projected area of wind turbine blades (Rotor diameter) is 59m. The tower is tubular and welded. The blades are made of reinforced fiber. They have installed 25 AE-59 turbine under Seguwantivu wind power (Pvt) Ltd and Vidatamunai wind power (Pvt) Ltd. So that 10MW supply can be obtain from each farm. Each wind turbine occupies approximately 0.25 hectares. The total land requirement will be 6.5 hectares for the entire 20MW. and the best length between two towers is 2.5 X height of tower, but here they have kept 130m length between two towers.

This turbine consist of variable pitch controlling system operated using hydraulic system. This pitch controlling is used to control the speed of the turbine to have maximum power output and it is used to break the turbine and hold it stop. And also there is a hydraulic operated disk break to stop the rotor.

And the gear box couple to the rotor increases the rotational speed up to 1500rpm with ratio 66 for the generator. It is a oil cooled gear box. The gearbox oil is circulated through a lubrication circuit which includes filtration and cooling (when oil temperature makes it necessary). And the gearbox is monitored by means of temperature sensors and oil level sensors, as well as the oil flow through the lubrication circuit.

And the output shaft of the gear box is coupled to the generator using elastic coupling. It carries the power from the gearbox high speed shaft to the generator. The coupling includes the disc brake, where a hydraulic caliper is applied only for parking issues or in case of emergency button is pressed.

It is possible to summarize important feature of the generator as follows;

· Synchronous Generator 850kW

WTG 800kWs net, generator has to produce the losses and auxiliary supplies.

· Salient Poles (4 poles, 1500 rpm nominal speed)

· Air to air heat exchanger

· Independent and Brushless excitation

V-f external adjustment

No maintenance needed

· Output voltage range 0-1000V (500-1000V)

· Output frequency range 0-50Hz (25-50Hz

It is important to turn the face of the turbine against the direction of wind. There for it should have a yaw mechanism. This mechanism of Gamesa AE-59 is actuated by two servomotors. To determine the direction of wind a sensor is used.

When we consider the electrical system of the system, it consists of a synchronous generator as mentioned above, a power converte, a distribution cabinet, a transformer and a control cabinet.

Around 700-800 rpm, excitation system is activated and voltage appears in stator of the generator. The excitation control of the generator has been adjusted so that a voltage proportional to the rotational speed (750rpm-500Vac 1500rpm-1000Vac) appears in the stator terminals. If the wind is high enough, the energy production is activated and the current demand from chopper is set.

The power convertor is used to convert the generated voltage into form of grid supply. The power convertor first converts generator output (single phase AC voltage) into DC voltage. Then that DC voltage inverts into three phase AC voltage with the frequency 50Hz.

To control all the system considering all feedback signals A Programmable Logic Controller (PLC) is used. It controls all safety conditions, yaw angles; pitch angle of blades, power output etc. the PLC is taking data of Wind Speed (Up to four anemometers optional), Wind Direction, Air Pressure, Air Temperature, Relative humidity (optional) and Rain sensor (optional).

After generation of electricity they are using 14 km long dedicated 33 kV, Elm conductor, concrete pole transmission line on Puttalam-Kurunegala Road up to Kalladi Grid Sub Station.

To control the wind farm and monitor the condition of the system a software system is used. The core of the software system is the SCADA (Supervisory, Control, and Data Acquisition), based on web technology where the redundancy, friability and connectivity are necessary properties. The main functions of the software system are;

• Display real information about wind farm state.

• Supervisory.

• Remote Commands Controls From the wind farm or out of it.

• Data Store.

• Reports.

• External Connectivity for receive set points.

• Power Control.

This system helps to monitor the system from any country. Even Gamasa Company is also always monitoring the system from Spain. Because they have responsibility for 5 years on these two wind farms. And this system gives alarm signals, errors of the system, energy production data and availability etc.

MAINTENANCES OF THE SYSTEM

To keep the system running without failure it is important to maintain the system well. They are following preventive maintenance program. Under that they do some special steps once six months. They do some basic things like Appling lubricating grease for main bearing, Change lubricant of gear box; Change hydraulic fluid etc. and also they have good corrective maintenance system.