Wind Farm Operates in Harmony With Park in Japan

Minamikyushu City, in the southern Satsuma Peninsula of Kagoshima Prefecture, is “Japan’s top tea-production region.” The city boasts the highest production and the largest growing area of tea among all cities, towns and villages in Japan. Minamikyushu City was created when Eicho, Chirancho and Kawanabecho merged in December 2007. Although tea production is thriving in all these three towns, the city’s tea brand has been standardized to “Chinrancha,” which is the most well-known.

The “Yume/Kaze-no-sato Agri-land Ei” on a hill by Eicho has become a park where both adults and children can enjoy such facilities as a camp site, hot spa and small animal park. Given its great wind conditions, the former Eicho constructed a wind farm facility with an output of about 500kW in March 2000, which became the park’s symbol. However, the facility was demolished in 2014 as it had grown old.

What now gives form to “Yume/Kaze-no-sato (village of dream/wind)” in the park’s name is the “Ei Wind Farm” with a total output of 16MW. Eight large wind turbines with an output of 2MW each were scattered on the hills around the park and are rotating over the tea fields.

Yonden Engineering Co Inc (Takamatsu City) constructed the Ei Wind Farm in July 2010 and provides operation & maintenance (O&M) services. The power producer is its subsidiary Ei Wind Farm (Takamatsu City). In March 2015, the wind farm’s total capacity was boosted to 16MW from 14MW by adding one more unit to the seven wind turbines with an output of 2MW each that had been set up when it was completed.

Yonden Engineering has abundant experience in designing and constructing wind power generation facilities. Designing and constructing Japan’s first find farm (20 units, 20MW) that started operation in Tomamaecho, Hokkaido, in 1999, the company is a sort of pioneer who established the grid connection technology for the wind power generation business in Japan.

In the area of wind farms and mega- (large-scale) solar power plants, Yonden Engineering has been financing power generation business as well as engineering, procurement and construction (EPC) services.

In fact, the Ei Wind Farm was initially planned to be a joint project financed by three firms including Yonden Engineering. However, following the other two firms’ withdrawal from the project, Yonden Engineering became the sole financer of the power generation business.

In Japan, large wind power generation facilities were initially constructed in Tohoku and Hokkaido, where wind conditions are good and only a few typhoons strike. Although wind conditions were good, business risk was considered high in the Kyushu region, which is struck by many typhoons. However, wind turbine design technology, which also featured measures against strong wind, gradually advanced. The Japanese Industrial Standards (JIS) Committee, in conjunction with the International Electrotechnical Committee (IEC), classified a wind turbine’s wind resistance into three stages, and “Class I” wind turbines can endure a 10-minute average wind speed of 50m/s.

At the Ei Wind Farm, The Japan Steel Works Ltd’s (JSW) wind turbines with an output of 2MW were adopted as a result of selection among Class I-specification wind turbines of Japanese manufacturers.

In Kyushu, it is also a challenge that the region is struck by lightning more than other regions in Japan. The adopted wind turbines are reportedly designed to withstand an electric charge of 600 coulombs when lightning strikes. Equipped with a material called “receptor” that protects blades when struck by lightning, the received electric current will be discharged into the ground through the tower’s downward conductor.

Partly because many areas around the wind turbines had already been developed as a park and pastures, their positions were unchanged as a result of environmental assessment. What became a serious restriction when determining the wind turbines’ positions was wireless communications. This was because some areas were “Fresnel zones”, which are important for such wireless communications as microwaves.

In wireless communication, it is required to secure a certain amount of space called a “Fresnel zone” around the radio transmission facilities. If there are any obstacles in the Fresnel zone, they could cause a communication failure. The 2MW-output wind turbines, which reach 100m at their highest points, were highly likely to become obstacles. As a result, the wind farm held discussions with the organization managing the wireless communication facility and decided to avoid the areas along hill ridges while seeking locations that would not cause communication failures.

According to the wind farm, although wind turbines are generally positioned along ridges at wind farms in the mountains, the wind turbines in Eicho were set up in an unusual pattern for this reason.

Many power producers have approached constructing additional wind turbines at existing wind farms, as the unit price of electricity rose in the wake of the feed-in tariff (FIT) scheme. If the plant increases the number of wind turbines and continues to connect them with the same grid point for selling power, its business performance will be determined by how much additional investment is required for the grid substation.

If the amount of power transmission increases as a result of large-scale expansion, extensive renovation will be required, because the existing substation’s capacity outperforms the initially estimated thermal capacity. If additional construction is modest compared with the previous grid capacity, the investment efficiency will be poor, and the power plant’s overall business performance will deteriorate as a result.

The Ei Wind Farm additionally constructed one wind turbine (2MW), because it could secure a new site for the wind turbine, and also the existing grid substation could be still used for expansion of up to one unit and 2MW. Products of Toshiba Mitsubishi-Electric Industrial Systems Corp (TMEIC) were adopted at the grid substation. After discussing with TMEIC about the expansion of a power generator with an output of 2MW, the wind farm found out it only needed to attach blowers on the heat radiator as a measure against boosted operation efficiency of step-up transformers.

If all the eight wind turbines fully operate and cause power transmission to increase and the temperature of step-up transformers to rise above a certain degree, the blowers will start and forcefully cool down the heat radiator. According to the wind farm, this improves the cooling effect and keeps the step-up transformers’ temperature from rising.

It has been eight years since the Ei Wind Farm was completed. Although there were no serious problems during that time, the plant is now facing some challenges from the perspective of component replacement and preventive maintenance.

In October 2014, JSW announced the recall of its 2MW-output wind turbine “J82-2.0,” and logged the cost required for component replacement (roughly 16 billion yen) as extraordinary loss in its consolidated interim results ended September 2014. The recalled wind turbines totaled 108 units in Japan. They included the seven wind turbines, which were operating at the Ei Wind Farm.

The component that was found defective was the bearing for pitch control to change the direction of the blades, and it could crack depending on the operation circumstances. Accordingly, the wind farm stopped its wind turbines and replaced the bearings after disconnecting the three blades from each tower. JSW bore the cost for this bearing replacement including the power sale loss while the operation stopped.

The wind farm also started considering repositioning the step-up transformers, which had been installed within the nacelle (the housing for a power generator and other items at the top of the tower) of each wind turbine, to the foot of the tower and putting a protective tape on the blade tips as measures to prevent future failures before they happen.

Considering transferring the step-up transfer in the nacelle to the foot of the tower, Yonden Engineering has actually brought down the transformers from three wind turbines. The company explained this was because “in consideration of the step-up transformer’s failure in the long run there was the risk that insulating oil might leak in the nacelle, in which the housed items are considerably vibrated and shaken.”

If the transformer is brought down to the bottom, the cables in the tower could become thicker because the electricity will be transmitted to the ground at 660V without being transferred, but the wind farm is planning to give priority to avoiding the risk of oil leaking inside the nacelle.

If oil leaks in the nacelle, it could catch fire from the arc (spark) generated from electric facilities by a lightning strike or some other reasons and could develop into a fire. In August 2017, a fire broke out at a wind turbine with an output of about 2MW in Karatsu City, Saga Prefecture, and the news was reported nationwide. In this accident, it was reported an arc had been generated and developed into a fire near a step-up transformer, starting from the nacelle itself and extending to the blades.

If a fire breaks out in the nacelle, nothing can be done until the fire naturally dies down because it is difficult to distinguish fire 65m above the ground. If such a fire occurred at the Ei Wind Farm located near a park, its impact would be immeasurable.

The plant put the protective tape on blade tips in order to prevent damage dubbed “erosion.” If a blade as long as 40m rotates, the speed near its tip will reach 300km/hour. If rain and dust repeatedly hit this area, the blade surface will increasingly grow worn and damaged. This is called erosion, which not only lowers power generation efficiency but also affects safety as the damage worsens.

The wind farm accordingly faces challenges such as repair and preventive measures, having frequently added caulking and paint. However, these measures also required work and time, as the facility could not be operated until the caulking and paint dried.

In collaboration with JSW, Yonden Engineering, for the first time, wrapped 5 to 6m of each blade tip with the protective tape. The wind farm used an adhesive tape of 3M that was highly ultraviolet-resistant and weather-resistant. The wind farm will consider whether it will adopt this tape on a full-scale by verifying the tape’s long-term service life from now.

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