Medium-Frequency Transformer Patents: Leaders & Filing Trends 2026
- Concentration at the top. Five assignees hold 65.9% of all 123 records in scope, and the leader alone accounts for 31 filings.
- Filing has plateaued, not grown. The complete-year window shows flat activity from 2021 to 2024 (7 to 7, 0% change), after a 2020 peak of 14.
- Claim space is dominated by two IPC subclasses. H01F (magnets, inductors & transformers) and H02M (power conversion) cover 66.7% and 43.1% of records respectively, leaving thermal and connector-level classes thin.
Filing growth compares 2021 (7 records) with 2024 (7) — a three-year span. 2024 is the most recent year we treat as complete: publication lags filing by roughly 18 months, so 2025 onwards are still filling in and any growth rate that ends there would understate the field. Top-5 share is the combined record count of the five largest assignees divided by all 123 records in scope (CR5), not by the ranked leaders only.
What this landscape covers
Medium-frequency transformer insulation design sits at the intersection of magnetics and power electronics: windings, insulating media and thermal paths that must survive higher switching frequencies than a line-frequency transformer ever sees. The 123 records in scope span filings from 2015 through mid-2026, drawn from a search built around partial discharge, dielectric loss, winding arrangement, leakage inductance and thermal management as the defining technical claims.
Filing activity is not evenly spread. A small group of assignees, several with backgrounds in rail traction and industrial power conversion, account for the bulk of the record count, while the rest of the field files once or twice and moves on. That pattern matters for anyone deciding where to file next: dense zones mean crowded claim language, thin zones mean open ground but also less prior art to build on.
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Filing trend and technology composition
Two views of the same 123 records: how filing activity has moved year over year, and which IPC subclasses carry the claim density.
A plateau after a 2020 peak
Filings ran from 7 in 2017 to a peak of 14 in 2020, then settled into a flat pattern — 7 in 2021 and 7 again in 2024, a 0% change across that span. 2025 and 2026 figures are still incomplete because publication lags filing by roughly 18 months, so the most recent years will fill in as more records publish.
Two subclasses dominate the claim space
H01F (magnets, inductors and transformers) appears in 66.7% of the 123 records and H02M (power conversion) in 43.1%, confirming that most filings combine magnetics claims with power-electronics context. H05K, H02J, B21D, H01L, H01R and B22D each cover a much smaller share, which is where structural, packaging and connector-level insulation work is comparatively under-claimed.
Shares are the percentage of the 123 records in scope. A patent can carry several IPC classes, so the shares add up to more than 100%.
Go deeper on Medium-Frequency Transformer Insulation Design with Eureka
This page is one run against one query. Ask Eureka your own question about medium-frequency transformer insulation design and every answer comes back with the patent numbers behind it.
Try EurekaMost-cited records in the corpus
US9437356B2 — Medium frequency transformer
The invention concerns a medium frequency transformer with a housing, in which numerous winding chambers, having primary and secondary windings, are disposed, wherein the housing is filled, at least partially, with an insulating liquid. Numerous winding chambers, filled with the insulating liquid, are disposed in the housing, and at least one winding is disposed in each winding chamber, such that, for the most part, only the windings are surrounded by the insulating medium. The winding chambers are sealed and separated from one another by insulating separating walls.Filed by STS Spezial-Transformatoren-Stockach GmbH & Co. KG, granted 2016-09-06.
| # | Publication no. | Patent title | Citations |
|---|---|---|---|
| 1 | US5892664A | Inverter for connecting a variable voltage power source to a utility grid | 46 |
| 2 | WO2018007514A1 | Transformer with a winding arrangemnet of LITZ wires | 32 |
| 3 | CN101795080A | 一种配电用三相电力电子变压器 | 27 |
| 4 | WO2014005806A1 | Electro-magnetic device comprising a cooling arrangement including a specifically arranged thermosyphon | 23 |
| 5 | DE10203246A1 | Mittelfrequenz-Transformator | 21 |
| 6 | EP2833378A1 | Transformer | 20 |
| 7 | CN107947146A | 基于模块化多电平变换器的直流电网及多层容错控制方法 | 19 |
| 8 | US3728655A | Medium frequency transformer | 19 |
| 9 | EP2696358A1 | Medium frequency transformer | 15 |
| 10 | US20140159846A1 | Medium frequency transformer | 14 |
Citation counts inside a searched corpus favour older records that have had more time to accumulate citations — read them as a signal of influence on the field, not of current technical relevance.
Patent titles are shown in the language they were filed in, not translated, so that each record stays verifiable against the original filing — a translated title will not match in Eureka or in any national register. Each row carries its publication number; clicking a row searches Eureka by that number.
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Browse MCP servers →What the numbers mean for a filing decision
Three findings from the dataset that change where a new filing or a design-around should look.
Five names occupy most of the claim space
The top five assignees combined account for 81 of the 123 records in scope, with the leader alone holding 31. That level of concentration means new entrants are more likely to find open ground in adjacent structural or thermal claims than in core winding-insulation claims already staked out by the incumbents.
Filing has plateaued since the 2020 peak
After reaching 14 filings in 2020, the field settled to a flat 7-to-7 pattern between 2021 and 2024. That is not a sign the technology is exhausted — high filing density in earlier years occupied core claim space, but it leaves room for narrower, more targeted filings rather than broad winding-architecture claims.
Europe leads filing office activity, China and the US close behind
Europe (EPO) receives the largest single share of filings at 27, with China and the United States each at 19 and WIPO (PCT) route filings at 12. That spread suggests insulation-design IP is being protected across multiple major markets rather than concentrated in one jurisdiction.
Eureka can read the same corpus for gaps instead of for coverage: under-claimed branches adjacent to medium-frequency transformer insulation design, with the prior art for and against each one.
Who is filing, and where the gaps sit
The ranked leaders come from rail traction, grid equipment and industrial power conversion backgrounds — but recent-year momentum has slowed even among the top names.
A single assignee holds the largest share
The top-ranked assignee accounts for 31 of the 123 records in scope, well ahead of fifth place at 6. That gap between first and fifth place is a useful proxy for how defensible the core winding-and-insulation claim territory already is.
Most filers appear once or twice
Below the top ten, which together hold 80.5% of all 123 records, the remaining ranked assignees contribute small, often single-filing counts. That long tail includes specialist transformer makers and component suppliers rather than diversified conglomerates.
Recent-year activity has cooled even among incumbents
Recent-year momentum data shows most of the historically active assignees recording zero filings in the latest year, with only the current leader still filing at all. That cooling, combined with the flat 2021–2024 trend, points to a field where core claims are settled and new activity is likely to be incremental.
| Assignee | Recent year | YoY |
|---|---|---|
| ABB (Schweiz) AG | 1 | — |
| Bombardier Transportation GmbH | 0 | — |
| Hitachi Energy Switzerland AG | 0 | — |
| Hitachi Energy Ltd | 0 | — |
| ABB Technology AG | 0 | — |
| STS Spezial-Transformatoren-Stockach GmbH | 0 | — |
| DaimlerChrysler Rail Systems Technology GmbH | 0 | — |
| Zhangjiagang Free Trade Zone Jinpin Chemical Machinery Equipment Co., Ltd. | 0 | — |
Where to take this analysis
The dataset points to a field with settled core claims and pockets of open ground in structural and thermal design.
Map the white space before filing
With H01F and H02M carrying most of the claim density, a new filing has a better chance in thermal management, connector-level insulation or hybrid solid-liquid systems where record counts are thin.
Explore white space in EurekaWatch the incumbents' next move
The current leader is still filing in the latest year while most other historically active assignees have gone quiet — that asymmetry is worth tracking before committing to a design direction.
Track assignee activity in EurekaCheck citation strength against filing date
The most-cited records in this corpus skew toward older filings; before relying on one as a design reference, confirm whether newer, less-cited filings have already narrowed its scope.
Review cited records in EurekaCommon questions on this landscape
One assignee leads the ranked field with 31 of the 123 records in scope, well ahead of the fifth-ranked assignee at 6. The top five assignees combined hold 65.9% of all records, so filing activity is heavily concentrated at the top rather than spread evenly across the 40 ranked companies. Below the top ten, most assignees appear with only a handful of filings each, forming a long tail of specialist and one-off filers.
No — the complete-year data shows filings flat at 7 in both 2021 and 2024, a 0% change across that span, after peaking at 14 in 2020. Figures for 2025 and 2026 are still incomplete because patent publication typically lags filing by around 18 months, so those years will rise somewhat as more records publish. Treat the plateau, not a decline, as the honest read on where the field stands.
US9437356B2, held by STS Spezial-Transformatoren-Stockach GmbH & Co. KG and granted in 2016, claims a medium-frequency transformer housing with multiple winding chambers, each containing at least one winding and filled with insulating liquid, separated by insulating walls. The design's core claim is that the windings — rather than the whole transformer core — are the primary target of the liquid insulating medium, achieved through sealed, separated winding chambers. Anyone designing a competing liquid-insulated, chamber-separated winding structure should review this filing's exact chamber and wall claim language before proceeding.
H01F (magnets, inductors and transformers) appears in 66.7% of the 123 records in scope, and H02M (power conversion, AC/DC and related) appears in 43.1%, making these the two dominant subclasses. H05K, H02J, B21D, H01L, H01R and B22D each cover much smaller shares, indicating that packaging, connector and casting-related insulation claims are comparatively under-explored. Because a single record can carry multiple IPC classes, these shares add up to more than 100% of the record total.
The evidence points to structural and thermal sub-areas below the two dominant IPC subclasses: winding-chamber sealing geometry, solid-liquid hybrid insulation interfaces, connector-level dielectric barriers and thermosyphon-integrated cooling paths all show thinner record counts than core winding-and-magnetics claims. These are not guaranteed-clear areas, but they carry less prior-art density than the H01F/H02M core, making them a reasonable starting point for narrower, more defensible claims. A freedom-to-operate search remains necessary before filing in any of these branches.
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Disclaimer. This page is generated from Patsnap Eureka data drawn from a limited snapshot of global patent and scientific-literature records, and is provided for general information and reference only.
Patent data carries inherent limitations: recent filings (typically the most recent 18–24 months) are under-counted due to standard publication lag; counts may be reported at either a patent-family or a patent-record basis and are not always directly comparable; classification, applicant-name, and citation data may contain errors, duplicates, or omissions; and the underlying search query defines and constrains the scope shown. As a result, the analysis may be incomplete or inaccurate and may not reflect the full technology landscape.
Nothing on this page constitutes an exhaustive prior-art, novelty, freedom-to-operate, or validity search, nor does it constitute legal, financial, investment, or professional advice, and it should not be relied upon as such. Any patent, commercial, or strategic decision should be verified independently and reviewed with qualified patent, legal, and domain professionals. Patsnap makes no warranties, express or implied, as to the accuracy, completeness, or fitness for any particular purpose of the information presented.
Machine translation. Assignee and organisation names originally recorded in Chinese, Japanese or Korean have been rendered into English by an AI translation step so that the tables stay readable. These renderings are best-effort and may not match a company’s registered English name; the original name is what the underlying patent record carries, and it is what any Eureka query launched from this page uses.