Sumida Prototype Brings 40 kHz Transformer to Grid
The 100 kVA medium-voltage prototype is an announced first step toward 35 kV-class isolation, with no efficiency data yet released.
Updated on Nov. 3, 2026 in Semiconductors
Sumida has built a 100 kVA medium-frequency transformer for solid-state transformer designs, developed with Infineon, which supplies the 3.3 kV CoolSiC switching devices on either side of it. This is an announced prototype, not a shipping product, and the announcement does not disclose efficiency, losses, cooling method, volume or weight.
Why it matters
Solid-state transformers replace bulky 50/60 Hz iron-core transformers with power electronics and a small high-frequency magnetic core, and raising the operating frequency to tens of kilohertz is what shrinks them. Demonstrating isolation and partial discharge performance at medium voltage is a step toward grid-scale hardware for data centers, fast chargers and microgrids.
The announced figures are a 100 kVA rating, a 40 kHz resonant frequency, an insulation test voltage above 20 kV and a partial discharge extinction voltage above 14 kV, with leakage inductance of about 150 μH. These are reported test values from the manufacturer, and the announcement offers no efficiency or loss data to benchmark against prior designs.
The players
Sumida
Sumida is a Japanese electronic components maker that designs magnetic components such as transformers and inductors.
Infineon
Infineon Technologies is a German semiconductor company whose CoolSiC silicon carbide power devices are used in high-voltage power conversion.
The details
A solid-state transformer uses power-switching semiconductors to convert voltage at high frequency and passes that energy through a small magnetic core, instead of relying on a large core running at mains frequency. Sumida supplied the magnetic materials, winding, thermal design and medium-voltage isolation, while Infineon supplied 3.3 kV CoolSiC devices, silicon carbide transistors rated for high voltage, for the switching stages on either side. Operating the core at 40 kHz reduces its size, and the leakage inductance of about 150 μH is a key parameter in how the converter stages exchange energy through the transformer.
Timeline
November 3, 2026: Sumida's announcement of the 100 kVA medium-frequency transformer was published.
The Tech Race
Solid-state transformer development is an active area where semiconductor makers such as Infineon and magnetics specialists such as Sumida are pairing devices with magnetic designs. Sumida calls this the first step toward 35 kV-class isolation, a projection that is not yet demonstrated.
This is a prototype and no availability, pricing or ship date was announced. Target uses named include AI data centers, EV fast charging, battery storage, renewables and microgrids, but none of these are currently served by this specific design.
The takeaway
Watch for published efficiency and loss figures, which are the numbers that will determine whether a 40 kHz solid-state design beats conventional transformers on cost and size. Sumida's stated next goal is 35 kV-class isolation, and progress toward it would confirm the trajectory.
Further reading
For more on the chips driving this kind of power conversion, see the Semiconductors section.
