Abstract
1. Introduction
2. Site description
3. KIST-20 project
4. Concluding remarks
Bibliography
Figures
C.S. Lee, K.H. Kim and H.C. Choi
Division of Mechanical/Control Systems
Korea Institute of Science and Technology (KIST)
Paper No.9412
Research activities on wind energy utilization in Korea are introduced briefly.
As an example, KIST-20 project is described which is the first trial to design and manufacture a wind turbine with our own technology.
The wind generator has a two blades rotor with a diameter of 14m and a power output of 20kW. After the component tests including blade bending test, it has been installed and test operated. In the next phase, it is planned to develope a large scale wind energy converter system.
In Korea the utilization of wind energy has been studied since the oil shock in 1970s, as in many other countries. It is considered as an energy source for the unelectrified remoted islands or as an alternative energy to diesel engine generators. KIST (Korea Institute of Science and Technology) has started the feasibility study on wind energy converter for the electricity supply by operating small wind generators (2 -5 kW power output) since 1974 [1-5]. At the beginning of study, some machines had shown failures mainly due to the high fluctuation and gust of wind. In 1980s KIST had performed the project successfully for the development of small wind energy converter, which had a mechanical governor for rotational speed control.
In 1984 KIST had started to operate a 14 kVA wind energy converter which was imported from Germany. This wind system was supplemented by a photovoltaic system with a power output of 2.4 kW with 2-axis tracking device. This project had been performed under the international cooperation with Germany [6]. From the measured weather data on site, it is shown a good correlation between wind and solar energy output, for example, during the low wind speed period (in summer), there is high solar insolation. That is the reason why a solar and wind combined system is studied. After that the KIST-20 project has been started with the purpose of development of our own technology for the system design and manufacturing, which is introduced in this paper briefly [7, 8].
Along the south and west coast of Korean peninsular the measured annual mean wind speed is about 4-4.5 m/s at the height of 10 m, so wind energy potential of this area is higher than that of the other place. Wolryoung on the west coast of Cheju island was selected for the site of this project (Fig.1). The site has a good wind condition. The annual mean wind speed is 4.5 m/sec at 10 m height from ground.
In selecting a site the availability of wind data, the accessibility from KIST, the distance from utility network and cost were mainly considered. The Wolryoung is the best place for these constraints. The wind data are obtained from previous projects performed at the same place. The accessibility is reasonable because it takes about three hours from KIST to the site by air and car, and the telephone line is provided. The 6.6 kV utility network is near the site and Cheju province offer this site for research.
This project is the first trial to design and manufacture a small scale horizontal-axis wind turbine with our own technology. Additionally, it should be the basis of the development of large scale system. This project is funded by Korean government and Korea Electric Power Corporation for three years. All the processes including the design of the system and the blade, the assembling and the ground testing, installation and the operation were done by KIST and the components were manufactured by the Korean companies.
3.1 System Description
This 20 kW wind turbine has a rotor with two blades, which rotates about a horizontal axis and is located downwind from the tower (Fig.2). Its technical specifications are shown in Table 1.
a) Rotor and blade
Two GFRP blades, hub, and a pitch control mechanism are the main parts of the rotor assembly. Each blade is 6.5 meters long and weight is 120 kg. It produces 20 kW at 84.7 rpm in 10 m/s wind speed at hub height (Fig. 3). Each blade has a nonlinear twist of 16.6 degrees and the section contour varies smoothly from an NACA 4424 (at root) to an NACA 4415 (at tip) (Fig.4). The blades are attached to a hub on the low speed shaft which drives the generator through a step-up gearbox. The hub is the rigid type and houses some of the part of the blade pitch change mechanism. The rotor diameter is 14 meters and the rotation is counterclockwise looking from downwind.
b) Nacelle arrangement
All of the rotating equipment for the wind turbine generator is located inside a nacelle and supported on a bedplade (Fig. 5). Support for the bedplate is provided by a gear-bearing assembly, turn table, and mounting frame. The bedplate is tilted on the gear-bearing assembly for the safe rotation of rotor blade against the striking of the tower. The mounting frame interfaces with the tower structure which provides support for the entire nacelle arrangement in the elevated position.
c) Blade pitch control
The pitch control mechanism consists of a hydraulic pump, the flow control valves, two readjusting springs, the hydraulic actuator and the linkage to regulate the pitch angle of blades. The actuating rod links the hydraulic actuator and the blade pitch change mechanism in hub through the low speed hollow shaft. At wind speeds below the cut-in and above the cut-out, the rotor blades are placed in a feathered position and no power is produced. The rotor blades are placed at a optimum position from the cut-in to rated wind speeds, and over the rated to the cut-out wind speeds, the pitch change mechanism reduces the pitch angle to regulate the rotor speed and the output power.
d) Transmission system
The transmission system consists of a 2 stage gearbox driven directly by low speed shaft by the rotor and hub. The 1: 21.43 speed-up ratio from low speed shaft to high speed shaft is provided by gearbox. The high speed output shaft drives a generator through flexible coupling. The low speed shaft is hollow so that the pitch regulating rod can be accomodated in it.
e) Electrical power system
The wind turbine electrical power system must produce power at a voltage and frequency compatible with the interfacing utility network. The power generation requirement imposed on the wind turbine design is 20 kW at a rated wind speed of 10 m/sec at hub height.
A simplified diagram of the wind turbine power distribution system is illustrated in Fig.6. The utility network must provide the power to initiate operation. The electrical power system for the wind turbine consists of the generator, the compensator, the utility interface switchgear and associated protective equipment. The generator is a 20kW, induction machine with a rated output voltage of 380 V, three phase, four wire, 60 Hz and a rated input of 1816 rpm.
f) Control system
The wind turbine was designed to be a fully automatic power generator tied to a utility network. To achieve this, the wind turbine control system is capable of monitoring wind conditions, maintaining nacelle alignment with the wind, controlling rotor speed and power level, and starting, synchronizing, and stopping the wind turbine in a safe manner. In addition, the control system must monitor essential parameters throughout the wind turbine to assure that critical components are operating within specified tolerances.
The control system to accomplish the majority of the control functions can be divided into five distinct control systems. These five control systems consists of rotor blade pitch control, yaw control, microprocessor control, the safety system and monitoring system.
g) Yaw system
The nacelle of the wind turbine generator and all of the equipment housed in the nacelle are supported by a turntable bearing which permits angular turning about the vertical axis to maintain proper alignment with the wind direction. This yawing action is achieved by worm and gear driven by an electric motor.
h) Tower
The tower for supporting the nacelle, the blades, and the equipment housed in the nacelle is 12 meters mono-pole type with four guyed wires.
Table 1 Technical data
|
Rotor |
|
|
|
|
- number of blades |
2 |
|
- diameter |
14 m |
|
|
- rotational speed |
84.7 rpm |
|
|
- location |
downwind |
|
|
- height |
12.5 m |
|
|
Blades |
|
|
|
|
- length |
6.5 m |
|
- material |
GFRP |
|
|
- swept area |
153 m² |
|
|
- airfoil |
NACA4415 - NACA4424 |
|
|
Tower |
|
|
|
|
-type |
4 wire guyed mono pole |
|
- material |
steel |
|
|
- diameter |
508 mm |
|
|
Gear Box |
|
|
|
|
- type |
2 stage |
|
- gear ratio |
1: 21.43 |
|
|
- rating |
31.3 kW |
|
|
Generator |
|
|
|
|
- type |
Induction |
|
- output |
20 kW |
|
|
- voltage |
3 x 380 V |
|
|
Control Systems |
|
|
|
|
- speed control |
variable pitch blade |
|
- blade pitch control |
electro-hydraulic |
|
|
- activation blade pitch |
hydraulic piston |
|
|
Performance |
|
|
|
|
- rated power output |
20kW |
|
- windspeeds |
|
|
|
cut-in |
4 m/s |
|
|
rated |
10 m/s |
|
|
cut-out |
20 m/s |
3.2 Installation and Testing
The wind turbine nacelle components were assembled and tested at KIST. The normal operating functions of various components were checked and the handling facilities for site erection/maintenance were also tested. In parallel with these works the tests for the blade were performed. The first blade was used for test purposes. These tests consisted of a modal survey followed by static bending tests.
The foundation for supporting the tower consists of a large reinforced concrete slab containing 32 cubic meters of concrete. And the tower tied with four guyed wires. The nacelle assembly was completed and the blades were attached to the hub at ground. This assembly was winched on the top of the tower with a crane.
It is expected that our experiences on wind energy researches will contribute to the enhancement of renewable energy utilization in Korea.
From the KIST-20 project and other earlier studies technical know-hows could be accumulated and can be applied for more reliable systems. After the field test and verification of performance of this installed 20 kW wind turbine it is planned, as the next phase, to develope a mid- and large-scale wind generator. A collaboration and exchange of experiences between Korea and China in this research phase will surely support the project, especially in the field of blade design and construction technology.
[1] Ch.O. Lee, et. al. "Study of the Wind Power Utilization as a Source of Energy", STF-74-2, MOST, April 1975
[2] J.W. Nam, et. al. "Development of Wind Energy Converter for Electrification and Pumping for the Mountain Area in Cheju island", BSJ82-772-2, KAIST, March 1976
[3] Ch.O. Lee, et. al. "Development of a Wind-electric Generator with Rated Capacity of 3, 5kW", STF-76-2, MOST, July 1977
[4] C.S. Lee, et. al. "Study on the Installation of 5kW Wind Turbine Generator" BSG383-1311-2, KAIST, Dec. 1979
[5] C.S. Lee, et. al. "Develpoment of 5kW Wind Turbine Generator at Cheju Island (I/II)", BSG474-1801-2/475-1804-2, KAIST, Sep. 1982
[6] C.S. Lee, et. al. "A Study on Korean-German Combined Solar-Wind Electric Energy Power System (I/II/III/IV)", N7-1969-2/47-2172-2/121-2465-2/263-2832-2, MOST, 1983/1984/1986/1987
[7] C.S. Lee, et. al. "A Study on Development of Small Horizontal-Axis Wind Generator System (I/II/III)", KRC-89G-T09, Korea Electric Power Corporation, 1990/1991/1992
[8] C.S. Lee, et al. "On Development of a 20 kW Horizontal-Axis Wind Turbine Generator", The 1st Korea-Italy Joint Workshop on New & Renewable Energy, Seoul Korea 1993
Fig. 1 Location of site
Fig. 2 KIST 20 kW wind turbine generator
Fig. 3. Power output characteristics
Fig. 6. Block diagram of wind turbine generator in grid connected operation
