Protection Relay Patents: Who Leads, Where Filings Are Cooling 2026
- Filing peaked in 2018 at 51 records and has declined every year since, falling to 13 by the 2022 midpoint and single digits by the most recent full year — a maturing claim space, not a growing one.
- G01R and H02H together account for the overwhelming majority of records, with 518 and 495 hits respectively out of 847 families, showing the field is still defined by classic measurement and protective-circuit claims rather than by digital or AI-based approaches.
- China now leads receiving offices with 175 filings, ahead of the United States at 169, and the six assignees with the strongest recent momentum all recorded zero filings in the latest year — a sign the incumbent bench has gone quiet just as the office mix has shifted.
Filing growth compares 2021 (26 records) with 2024 (25) — 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 847 records in scope (CR5), not by the ranked leaders only.
What this patent set actually covers
Protection relays and fault location sit at the intersection of two IPC families: G01R, which covers electric and magnetic measurement, and H02H, which covers protective circuit arrangements. Together they account for the large majority of the 847 families in this dataset, meaning claims here are still won or lost on how a fault is measured and how a circuit is protected — not on the surrounding data pipeline. The search string ties this to specific protection techniques: differential protection, distance protection, travelling wave methods, selectivity coordination, and the IEC 61850 communication standard used in substation automation.
Smaller but present clusters in H02J (grid systems), G06F (digital processing), H01H (switches), H04B (transmission) and G06N (AI-based computing) show where the field is starting to touch adjacent domains, though each remains a minority slice next to the measurement and protective-circuit core. Publication naturally lags filing by roughly eighteen months, so the drop shown in the most recent year is partly a reporting artefact rather than a real collapse in activity.
Filing trend and jurisdictional spread
The filing curve and the receiving-office mix together describe a technology area that expanded through the late 2010s and has been retreating since, while the geographic centre of gravity has moved toward China.
A peak in 2018, a steady decline since
Filings rose to a peak of 51 in 2018, roughly matching the 48 recorded in 2017, then declined through the midpoint year of 2022 at 13 and continued down toward single digits by 2026. Because the most recent year is partial and publication lags filing by about eighteen months, the tail understates true recent activity, but the multi-year downward slope from 2018 onward is a genuine trend rather than a reporting gap.
Measurement and protective circuits dominate the classification mix
G01R (518 records) and H02H (495 records) are the two anchor subclasses, with most families touching both. H02J, G06F, H01H, H04B, G05B and G06N appear in far smaller numbers, indicating that grid-systems integration, digital processing and AI-based fault analysis remain secondary themes rather than the dataset's core.
Shares are the percentage of the 847 records in scope. A patent can carry several IPC classes, so the shares add up to more than 100%.
Go deeper on Protection Relays and Fault Location with Eureka
This page is one run against one query. Ask Eureka your own question about protection relays and fault location and every answer comes back with the patent numbers behind it.
Try EurekaThe most-cited prior art anchoring this space
Time domain voltage travelling-wave differential protection for VSC-HVDC lines
This filing from Tianjin University addresses voltage travelling-wave differential protection for VSC-HVDC transmission lines, explicitly accounting for frequency-dependent line parameters. It calculates characteristic impedance and propagation coefficient in the time domain before comparing collected voltage and current waveforms, aiming at more accurate and faster fault identification than frequency-independent differential schemes.Filed by a university rather than an incumbent equipment maker, this record illustrates how travelling-wave differential protection for HVDC lines is being advanced from the academic side of the field.
| # | Publication no. | Patent title | Citations |
|---|---|---|---|
| 1 | US6798211B1 | Power line fault detector and analyzer | 211 |
| 2 | US5729144A | Systems and methods for determining location of a fault on an electric utility power distribution system | 161 |
| 3 | US5428549A | Transmission line fault location system | 134 |
| 4 | US20130096854A1 | Fault Location Using Traveling Waves | 132 |
| 5 | US5455776A | Automatic fault location system | 132 |
| 6 | US4812995A | Adaptive Kalman Filtering in fault classification | 125 |
| 7 | US6396279B1 | Method and device for testing differential protection relays or differential protection relay systems | 117 |
| 8 | US4797805A | Fault location in a power supply network | 73 |
| 9 | US20150081235A1 | Fault location using traveling waves by calculating traveling wave arrival time | 72 |
| 10 | US20210293873A1 | Transient based Fault Location Method for Ungrounded Power Distribution Systems | 66 |
Citation counts reflect influence within the searched corpus and favour older filings; treat them as a marker of foundational prior art rather than of current commercial relevance.
Each row carries its publication number; clicking a row searches Eureka by that number.
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Three patterns stand out once volume, classification and geography are read together: a shrinking filing curve, a classification mix still anchored in classic measurement and circuit claims, and a citation base that is decades old relative to the newest applicants.
The curve has turned down, not up
From a 2018 peak of 51 records, filings fell through a midpoint of 13 in 2022 to single digits approaching 2026. That is consistent with a field where the core protective techniques — differential, distance, travelling-wave — have already been broadly claimed, pushing new entrants toward narrower refinements rather than foundational filings.
Two subclasses still carry the field
G01R and H02H together dominate the 847-family set, while G06N (AI-based computing) appears in only 7 records. Algorithmic fault-classification approaches exist but are a small fraction of the corpus, which is notable given how much industry discussion assumes AI-driven protection is already mainstream in the patent record.
China has edged ahead of the US as receiving office
China's 175 filings now lead the United States' 169, with EPO at 145, WIPO/PCT at 68, Japan at 61 and India at 53. A filing strategy built only around US and European coverage would miss the office that currently receives the most applications in this space.
The most-cited prior art predates the recent filing wave
The highest-cited records in this corpus are power-line and transmission-line fault-location patents from well before the 2017-2026 window tracked here. High citation counts concentrate on older, foundational filings by construction of the corpus, so they should be read as markers of influence, not as evidence that those approaches are still the most actively claimed.
Eureka can read the same corpus for gaps instead of for coverage: under-claimed branches adjacent to protection relays and fault location, with the prior art for and against each one.
Assignees, momentum and where the bench has gone quiet
The strongest recent-momentum names in this dataset — spanning US, European, Japanese and Swedish-heritage grid equipment makers — all show zero filings in the latest tracked year, a pattern distinct from the field simply having no active filers.
Collaboration is limited and concentrated
Only ten co-assignee pairs appear across the corpus. The strongest is a Japanese pairing between a major electrical manufacturer and a utility holding company at 5 joint records, followed by two pairings involving a European industrial group with named individual co-inventors at 4 and 3 records respectively. Most families in this space are filed by a single assignee.
Established filers have paused, not withdrawn
Six of the assignees with historically strong filing activity — including major US, German, Japanese and Swedish-heritage names — recorded zero filings in the most recent year, one with a documented -100% year-on-year change. Given the publication lag, this likely reflects a slowdown in the pipeline reaching publication rather than a confirmed exit from the field.
Filing strategy already spans six major offices
With meaningful volume across China, the United States, EPO, WIPO/PCT, Japan and India, incumbents in this space are already filing across a broad jurisdictional footprint. New entrants competing on protective-circuit or travelling-wave claims should expect prior art search and freedom-to-operate work to span all six.
| Assignee | Recent year | YoY |
|---|---|---|
| Schweitzer Engineering Laboratories | 0 | -100% |
| Siemens | 0 | — |
| Toshiba Corporation | 0 | — |
| ASEA Brown Boveri (ABB) | 0 | — |
| General Electric Technology | 0 | — |
| Mitsubishi Electric Corporation | 0 | — |
| Alstom Technology Ltd | 0 | — |
| ABB Technology Ltd | 0 | — |
Where to take this analysis
The dataset points to a field with concentrated core claims and a cooling filing curve, which changes how a freedom-to-operate search or a white-space filing strategy should be scoped.
Map claim boundaries around the top-cited prior art
Before drafting new claims in differential or distance protection, work through what the highest-cited records — several dating to the 1990s and early 2000s — actually protect, since a large share of the field's foundational logic traces back to a handful of filings.
Explore prior art in EurekaTrack the quiet incumbents for renewed filing
Six historically active assignees show zero filings in the latest year. Set alerts on these names specifically, since a publication-lag rebound would be the clearest signal of where competitive filing resumes first.
Set up assignee tracking in EurekaScope filings toward China and the US together
With China now marginally ahead of the US in receiving-office volume, a filing or FTO strategy built around only one of the two would miss meaningful coverage; treat both offices as first-tier for this technology.
Run a jurisdictional search in EurekaCommon questions about protection relay and fault-location patents
The filing trend in this dataset peaked at 51 records in 2018 and has fallen in most years since, reaching 13 by the 2022 midpoint and single digits approaching 2026. This pattern is typical of a technology area where the core protective techniques — differential protection, distance protection, travelling-wave detection — were heavily claimed in the preceding decade, leaving later filers to pursue narrower refinements rather than foundational patents. It is worth remembering that publication lags filing by roughly eighteen months, so the very latest year in any such chart is always undercounted relative to what will eventually be published.
This dataset's assignee ranking is rendered separately in the page's data tables rather than summarized as a hand-picked list, because rankings shift as new records publish. What can be said directly is that several long-standing US, European, Japanese and Swedish-heritage grid equipment manufacturers show strong historical filing activity but zero filings in the most recent tracked year, which is a distinct signal from a newer entrant building momentum. Reviewing the ranking table alongside the momentum figures gives a more accurate picture than either alone.
Differential protection compares current or voltage measurements at two ends of a protected line segment and trips when the difference exceeds a threshold consistent with an internal fault, while travelling-wave fault location times the arrival of a fault-generated voltage or current wavefront at one or more measurement points to calculate distance to the fault. Both appear as distinct search terms in this dataset's classification, and travelling-wave methods feature prominently in HVDC-specific filings such as the representative VSC-HVDC record covered on this page. Differential schemes tend to dominate AC distribution protection, while travelling-wave approaches are increasingly associated with HVDC transmission lines where fast, accurate fault location matters more given the absence of natural zero-crossings.
In this dataset China is the leading receiving office with 175 filings, narrowly ahead of the United States at 169 and well ahead of the EPO, WIPO/PCT, Japan and India. This reflects both the scale of grid infrastructure build-out in China over the tracked period and the general pattern of Chinese applicants filing domestically first before pursuing international routes such as PCT. It does not necessarily mean Chinese assignees hold the strongest claims globally — office of first filing and eventual enforcement jurisdiction are separate questions that require a closer look at family extension patterns.
Only marginally so far based on IPC classification: G06N, the subclass covering AI-based computing methods, appears in just 7 of the 847 records in this dataset, compared with 518 for G01R measurement claims and 495 for H02H protective-circuit claims. This suggests that despite industry discussion of machine-learning-based fault classification, the documented patent record for this specific search scope is still dominated by classical measurement and protective-circuit approaches. It represents one of the more clearly under-claimed branches identified in this landscape, though a broader search scope beyond this dataset's specific IPC and keyword combination might surface more AI-related activity.
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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.