On Feb. 26 at the Hyosung Heavy Industries Changwon Plant 1 in Changwon, South Gyeongsang. Massive cylinders, big enough that you would have to look down from the height of a 10-story building, caught the eye first. Workers in sky-blue dustproof suits were sweating as they wound copper wire as thick as a person's wrist around the cylinders. More than about 20 processes, including insulating material assembly, lead bending, and drying and compression, were carried out simultaneously.
Except for stepping on a foot pedal to rotate the cylinder, most of the work was done by hand. The copper wire is made by coating 99.99% pure copper with insulating paper. Because it must be wound onto the cylinder, the wire has to be turned upward midway, and the wire must not be damaged at that point. Extremely delicate welding is also required halfway through. The cylinder measures 2.5 meters in height and 3 meters in diameter.
Choi Young-sang, head of the ultra-high-voltage transformer structural design team at Hyosung Heavy Industries, said, "The allowable tolerance for winding work (the difference from the design) is only 2 mm," and noted, "Because it requires advanced skills, how many skilled workers you can secure determines the competitiveness of corporations."
If anything is even slightly misaligned, other design values all go off, so worker proficiency is considered the most important factor in winding, the core process in ultra-high-voltage transformer manufacturing. The average length of service for employees performing winding at the Changwon plant is 20 years. It is said that to handle the most difficult welding work requires 10 years, and even for relatively less demanding low-voltage winding work, about three years of training is needed.
For this reason, unlike many other manufacturing sites where robots are being adopted quickly, power equipment plants, including those for ultra-high-voltage transformers, have been slower to automate. However, the high proportion of manual work by skilled workers also serves as a barrier that makes it difficult for other companies to enter the market.
Hyosung Heavy Industries, which is expanding its plants amid a boom in the ultra-high-voltage transformer market, is preparing by securing skilled personnel in advance. Since 2024, it has been hiring additional staff at 50% to 100% of existing winding personnel levels, deploying them to assist and training them. Currently, about 100 employees perform winding work at the Changwon plant, and the total headcount across Plants 1 to 4, including partners, is around 3,200.
How much design manpower you can secure is also important. That is because specifications for power equipment vary widely by client. Depending on the scale of the power grid to be installed, the transformer capacity, tap changing, core sheet size, and other specs all differ, and designs are tailored accordingly.
A Hyosung Heavy Industries official said, "There is even a saying that 'there is no identical piece of power equipment,'" adding, "European clients in particular tend to have stringent requirements." In fact, a Norwegian client once attached a condition to build the transformer to the shape of a tunnel, saying the tunnel height along the transport route was low.
Among the companies capable of making ultra-high-voltage transformers in the global market, only three to four can meet all client requirements, including those in Europe. A Hyosung Heavy Industries official explained, "By securing many skilled production and design personnel and winning clients' trust, we were able to wedge into the European market, which had been dominated by global firms such as Siemens and General Electric (GE)."
The Changwon plant visited that day was also undergoing expansion. On the site near the yard at Plant 3, where ultra-high-voltage transformers awaiting export were stored in a row, construction heavy equipment was constantly coming and going as work continued. When the approximately 29,600-square-meter transformer production facility is completed next July and operations ramp up, the volume Hyosung Heavy Industries can produce at the Changwon plant will increase by about 20%.
The expanded facilities will also produce high-voltage direct current (HVDC) products, which will shape the future of the power equipment industry. HVDC is a core technology that reduces power loss during long-distance transmission and reliably integrates large-scale renewable energy. It is essential to the government's "West Coast energy highway" project connecting offshore wind farms with the greater Seoul area.
Hyosung Heavy Industries plans to complete development of 2-gigawatt (GW) HVDC technology needed for the West Coast energy highway project by the end of next year. Its independently developed 200-megawatt (MW) voltage-source HVDC technology was applied to the Yangju substation last year.
The share of production for the U.S. market is also expected to grow. For now, local production is mainly carried out at the ultra-high-voltage transformer plant in Memphis, Tennessee, acquired in 2020. That plant is also being expanded, and when completed in 2028, its capacity is expected to increase by more than 50%. Hyosung Heavy Industries has maintained the No. 1 market share in the U.S. 765-kilovolt (kV) ultra-high-voltage transformer market since the early 2010s.
The ultra-high-voltage transformer market is booming to the point that, due to a shortage of production slots, even if you place an order now you must wait at least two years. Jang Jae-sung, managing director at Hyosung Heavy Industries and head of the Changwon plant, said, "Just a few years ago, even overseas power industry clients, who know the sector best, were unsure whether the boom would last more than five years," adding, "Now, many expect the boom to continue for more than 10 years."