Transformer Manufacturing: ABB Robots Stack the Core

How transformer manufacturing went from hand stacked cores to robot cells, why the shortage hits data centers, and how ABB IRB 6740 robots now stack cores.

INDUSTRIAL ROBOTICS

Chat With Robot

10/2/20265 min read

Transformer manufacturing has become a bottleneck for the power grid. Data centers and grid upgrades compete for the same units, and lead times for the largest transformers now run to years. One slow step sits in the middle of every transformer: the core, a stack of thousands of thin steel sheets that people have laid by hand for more than a century. This post follows the core from the first closed-core transformers of the 1880s to the cutting lines that automated it, then looks at ABB robots now stacking cores in China and at what the shortage means for the next few years.

White ABB robot arms with long blue vacuum gripper frames lifting thin steel sheets onto a core stacking table
White ABB robot arms with long blue vacuum gripper frames lifting thin steel sheets onto a core stacking table

ABB IRB 6740 robots with vacuum grippers stacking transformer core laminations at Sieyuan Toshiba in Changzhou, China. Photo: ABB

How transformer cores were built by hand

In 1831 Michael Faraday wound two coils on an iron ring and showed that a current in one induced a current in the other. In 1836 Nicholas Callan at Maynooth College built an induction coil and saw that more turns on the secondary winding gave a higher voltage. The practical transformer came in 1885, when Károly Zipernowsky, Ottó Bláthy and Miksa Déri at the Ganz works in Budapest built efficient closed-core transformers that made AC distribution workable. In 1886 William Stanley built transformers for an early AC lighting system in Great Barrington, Massachusetts. The basic recipe of copper windings around a laminated iron core has not changed much since.

A round early transformer with dark wire windings and a wooden lid on a green museum stand
A round early transformer with dark wire windings and a wooden lid on a green museum stand

One of the first Déri, Bláthy and Zipernowsky transformers, built in Budapest in 1885, in a museum display. Photo: Zátonyi Sándor (ifj.) / Wikimedia Commons (CC BY-SA 3.0)

Most of the hand labor goes into the core. To cut eddy current losses, it is built from thin sheets of electrical steel, each insulated from the next, and thinner sheets mean lower losses but more sheets to cut and stack. In large power transformers the sheets overlap at the corners in careful patterns. ABB says that stacking one large core by hand traditionally took eight to twelve workers three to five days, and that the strain of the job led to uneven stacks, which raise core losses and noise.

Workers in hard hats and grey overalls laying long steel sheets onto yellow and blue stacking frames
Workers in hard hats and grey overalls laying long steel sheets onto yellow and blue stacking frames

Workers stacking transformer core laminations by hand, the job the robot cell replaced at Sieyuan Toshiba. Photo: ABB

Automation started with cutting. Machine builders such as Georg in Germany built lines that cut grain-oriented steel into laminations, and Georg's later robotline machines cut and stack complete cores for distribution transformers from 100 kVA to 15 MVA without manual stacking. Transformers Magazine credits the Italian firm L.A.E. with installing the first articulated robots for automatic core stacking. Large power transformer cores, with sheets several meters long, stayed mostly manual because the sheets are big and heavy and the tolerances are tight.

A museum exhibit of a tall transformer limb with copper windings partly cut away around a laminated steel core
A museum exhibit of a tall transformer limb with copper windings partly cut away around a laminated steel core

One limb of a power transformer with its windings cut open to show the stacked steel laminations of the core. Photo: Technisches Museum Wien via Wikimedia Commons (public domain)

The transformer shortage and the first big robot cells

Demand has outrun supply. POWER Magazine wrote in January 2026 that years of underinvestment, a post-pandemic surge in construction and electrification, and price swings in grain-oriented electrical steel and copper had pushed lead times for large power and generator step-up transformers far beyond historical norms. Utilities now order transformers and switchgear years ahead, and data center builders compete for the same units. Construction firms report rearranging schedules and locking in equipment earlier than ever, because access to transformers can decide which projects go ahead. Equipment makers have answered with new factories.

A large grey substation transformer with tall insulator bushings and cooling radiators
A large grey substation transformer with tall insulator bushings and cooling radiators

A 138 to 12.5 kV power transformer in a substation, 2024. Photo: Yoshieslunchbox / Wikimedia Commons (CC BY-SA 4.0)

On 15 September 2026 Hitachi Energy announced a $528 million transformer factory, its largest US investment to date, in Gallman, Copiah County, where it already employs 475 people making small power transformers. The plan adds 654 jobs, with construction starting late this year and production in 2029. The company is buying a 45-acre parcel in the Copiah County Industrial Park, and the state is supporting it through its MFLEX tax incentive. Utility Dive reported that it will double Hitachi's US output of small and medium power transformers. Hitachi Energy grew out of ABB's former Power Grids business, which ABB sold to Hitachi in stages between 2020 and 2022.

A long aisle between rows of black server racks under a curved metal ceiling
A long aisle between rows of black server racks under a curved metal ceiling

Server racks in the Virginia Tech data center, the kind of load driving new transformer demand. Photo: Christopher Bowns / Wikimedia Commons (CC BY-SA 2.0)

On 21 September 2026 ABB announced China's first automatic core stacking system for large five-limb transformers, at Changzhou Sieyuan Toshiba Transformer. ABB IRB 6740 robots stack 60,000 silicon steel laminations up to 4.5 meters long to a tolerance of 0.5 mm, and about 90 percent of the process is automated. The cell was designed and fully simulated in RobotStudio and runs on ABB's OmniCore controller. ABB says no-load losses in the finished transformers fell by 1.5 percent. Mingfang Li, deputy general manager of Sieyuan Toshiba, said the plant has cut core losses, made quality more consistent and "greatly reduced the physical strain on frontline workers."

Several white ABB robots with blue vacuum frames working over a large rectangular steel core on a stacking table
Several white ABB robots with blue vacuum frames working over a large rectangular steel core on a stacking table

ABB IRB 6740 robots placing laminations on the automatic core stacking line at Sieyuan Toshiba. Photo: ABB

Where transformer manufacturing goes next

Other plants are likely to copy the Sieyuan approach, starting with core stacking, since it is slow and heavy work and it directly affects losses. After that come the steps around it: moving laminations from the cutting line, handling windings, assembling tanks and testing. Several robots working on one long core have to move together, which is what ABB's MultiMove function does on a single controller. ABB robots already assemble switchgear for the grid, as our post on switchgear and drones describes.

A large grey power transformer on a yellow base inside a tall white factory hall with overhead cranes
A large grey power transformer on a yellow base inside a tall white factory hall with overhead cranes

A finished large power transformer in the test hall at Sieyuan Toshiba. Photo: ABB

A core stacking cell costs a lot and has to handle many core designs, stepping patterns and sheet sizes, which is why ABB needed fast switching and error correction in the Sieyuan control software. Steel quality and supply still limit output, robots or not. And the shortage is partly a people problem: winding, insulation work and final assembly still need skilled workers, and new plants like Gallman will have to train hundreds of them.

A row of enclosed robot cells with glass walls on an electrical equipment assembly line
A row of enclosed robot cells with glass walls on an electrical equipment assembly line

The robotic switchgear assembly line JOT Automation built for ABB Smart Power in Vaasa, Finland. Photo: ABB

Homes feel all of this through the grid. Every new housing estate, heat pump and electric car charger hangs on a transformer somewhere, usually a pole-mounted or pad-mounted distribution unit. When those take a long time to deliver, new connections wait. Faster and more consistent core stacking could shorten delivery times in the plants that adopt it, though steel, windings and skilled labor will still set the pace. Lower core losses also mean less energy wasted over a transformer's working life.

Overhead lines, steel gantries and transformer equipment in an outdoor electrical substation
Overhead lines, steel gantries and transformer equipment in an outdoor electrical substation

Transformers and connections at the high voltage substation in Pont-l'Abbé, France, 2022. Photo: PtiBzh / Wikimedia Commons (CC0)

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