Milestone-Proposal talk:Sakuma Frequency Converter Station, 1965

Advocates’ Checklist (Read Only; Do Not Edit)

1. Is the proposal for an achievement rather than for a person? If the citation includes a person's name, have the proposers provided the required justification for inclusion of the person's name?
2. Was the proposed achievement a significant advance rather than an incremental improvement to an existing technology?
3. Were there prior or contemporary achievements of a similar nature? If so, have they been properly considered in the background information and in the citation?
4. Has the achievement truly led to a functioning, useful, or marketable technology?
5. Is the proposal adequately supported by significant references (minimum of five) such as patents, contemporary newspaper articles, journal articles, or citations to pages in scholarly books? At least one of the references should be from a peer-reviewed scholarly book or journal article. The full text of the material, not just the references, shall be present. If the supporting texts are copyright-encumbered and cannot be posted on the ETHW for intellectual property reasons, the proposers shall email a copy to the History Center so that it can be forwarded to the Advocate. If the Advocate does not consider the supporting references sufficient, the Advocate may ask the proposer(s) for additional ones.
6. Are the scholarly references sufficiently recent?
7. Does the proposed citation explain why the achievement was successful and impactful?
8. Does the proposed citation include important technical aspects of the achievement?
9. Is the proposed citation readable and understandable by the general public?
10. Will the citation be read correctly in the future by only using past tense? Does the citation wording avoid statements that read accurately only at the time that the proposal is written?
11. Does the proposed plaque site fulfill the requirements?
12. Is the proposal quality comparable to that of IEEE publications?
13. Are any scientific and technical units correct (e.g., km, mm, hertz, etc.)? Are acronyms correct and properly upper-cased or lower-cased? Are the letters in any acronym explained in the title or the citation?
14. Are date formats correct as specified in Section 6 of Milestones Program Guidelines? Helpful Hints on Citations, plaque locations
15. Do the year(s) appearing in the citation fall within the range of the year(s) included at the end of the title?
16. Note that it is the Advocate's responsibility to confirm that the independent reviewers have no conflict of interest (e.g., that they do not work for a company or a team involved in the achievement being proposed, that they have not published with the proposer(s), and have not worked on a project related to the funding of the achievement). An example of a way to check for this would be to search reviewers' publications on IEEE Xplore.
17. Are the GPS coordinates correct and in decimal format?
18. Is the proposed achievement controversial because of various reasons including but not limited to: ecological, environmental, social impact, political scandal, etc.? (A relatively simple Google search on the achievement by the advocate, combined with words such as "protest", "scandal", "environmental impact" should be sufficient to alert the advocate.)

Independent Expert Reviewers’ Checklist

1. Is suggested wording of the Plaque Citation accurate?
2. Is evidence presented in the proposal of sufficient substance and accuracy to support the Plaque Citation?
3. Does proposed milestone represent a significant technical achievement?
4. Were there similar or competing achievements? If so, have the proposers adequately described these and their relationship to the achievement being proposed?
5. Have proposers shown a clear benefit to humanity?

In answering the questions above, the History Committee asks that independent expert reviewers apply a similar level of rigor to that used to peer-review an article, or evaluate a research proposal. Some elaboration is desirable. Of course the Committee would welcome any additional observations that you may have regarding this proposal.

Submission and Approval Log (For staff use only)

Submitted date: 21 July 2025
Advocate approval date:
History Committee approval date:
Board of Directors approval date:

Citation as originally submitted -- Administrator4 (talk) 17:08, 23 July 2025 (UTC)

Sakuma Frequency Converter Station, 1965

The Sakuma Frequency Converter Station, completed in 1965 by Electric Power Development Co., Ltd., enabled the first large-scale power exchange between Japan’s eastern 50 Hz and western 60 Hz grids via a 300 MW motor-generator frequency converter. This achievement addressed a long-standing national frequency division, improving grid reliability, resilience, and laying the foundation for Japan’s future energy interconnection infrastructure.

Expert Reviewer's Report_1_Mukaiyama uploaded by Advocate -- Tomohiro Hase (talk) 13:10, 24 July 2025 (UTC)

Review Report: Sakuma Frequency Converter Station, 1965
Reviewer: Katsumasa Mukaiyama, Tohoku Electric Power Network.
Date: July 24, 2025

(1) Is suggested wording of the Plaque Citation accurate?

Yes. The proposed citation —
"In 1965, the Sakuma Frequency Converter Station became the world’s first facility to connect power systems operating at different frequencies using high-voltage synchronous machines. It enabled the transfer of power between Japan’s eastern 50 Hz and western 60 Hz grids, providing flexibility and stability to the country’s electric power network." —
is accurate and appropriately concise. It clearly describes the technical breakthrough (interconnection via high-voltage synchronous machines) and its historical and national significance (first in the world, benefits to Japan’s grid).

(2) Is evidence presented in the proposal of sufficient substance and accuracy to support the Plaque Citation?

Yes. The proposal provides sufficient and technically accurate evidence, including references [1]–[6], to support the claim that the Sakuma Frequency Converter Station was the world’s first facility of its kind. Notably, Reference [3] (H. Honda, "Construction of Sakuma Frequency Converter Station," JEC, 1965) details the design, implementation, and operational principles of the system. The proposal also includes clear historical documentation of Japan’s east-west frequency divide and the technical approach chosen for bridging it.

(3) Does proposed milestone represent a significant technical achievement?

Yes. The Sakuma facility represents a globally significant milestone in power systems engineering. As stated in the "Historical Significance" section, it was "the world’s first frequency converter station employing three 100 MVA synchronous machines operating at 275 kV." This approach, as opposed to mercury arc valves or early solid-state converters, provided a reliable and controllable mechanism for power transfer between two asynchronous networks. In addition, traditional methods of frequency conversion, such as dual-frequency generation or isolated converter stations, were limited in capacity and slow in response, but Sakuma's use of a motor-generator system enabled rapid bidirectional power exchange, allowing frequency decoupling and real-time grid support. The successful long-term operation (since 1965) of such a complex electromechanical system at high voltage and large capacity reflects a major technical accomplishment in system integration, power electronics (of its time), and synchronous machine control.

(4) Were there similar or competing achievements? If so, have the proposers adequately described these and their relationship to the achievement being proposed?

Yes. The proposers adequately mention European HVDC Systems and other similar technologies and clearly differentiate Sakuma’s uniqueness. The section “Features Setting This Work Apart from Similar Achievements” discusses other early frequency conversion attempts, including mercury-arc converter systems in Europe. However, Sakuma was the first to apply high-voltage synchronous machines for such a purpose at scale. This method provided operational advantages such as reactive power support, higher efficiency, and long-term reliability. The proposal effectively demonstrates that no comparable facility of this capacity and approach existed at the time.

(5) Have proposers shown a clear benefit to humanity?

Yes. The Sakuma Converter Station significantly improved the stability and flexibility of Japan’s power system, which remains split into 50 Hz and 60 Hz regions. This facility allowed mutual power support between regions during peak loads and emergencies, including earthquakes and natural disasters, enhancing national resilience. The design became a model for subsequent frequency converter installations worldwide. In this sense, the milestone reflects both national infrastructure enhancement and broader influence on global engineering practices.

Conclusion:
The Sakuma Frequency Converter Station of 1965 is a pioneering achievement in electrical engineering. It represents the first successful implementation of high-voltage synchronous machines to interconnect asynchronous power grids. The technology addressed a critical infrastructure challenge in Japan and has had enduring influence on global grid interconnection methods. Given the technical innovation, historical importance, and continued operational legacy, I strongly recommend this proposal for designation as an IEEE Milestone.

[Advocate's remarks] Mr. Mukaiyama is an expert engineer of the Tohoku Electric Power Network co.

Expert Reviewer's Report_2_Taoka uploaded by Advocate -- Tomohiro Hase (talk) 01:20, 27 July 2025 (UTC)

Dear Professor Hase,

I will send my review report you requested.
Please find it below:

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Review Report: IEEE Milestone Proposal - Sakuma Frequency Converter Station, 1965

To: IEEE History Committee
From: Hisao Taoka /Reviewer
Date: July 27, 2025
Subject: Review of Milestone Proposal: Sakuma Frequency Converter Station, 1965 (Docket #: 2025-18)

I have reviewed the proposal for the Sakuma Frequency Converter Station, 1965, to be designated as an IEEE Milestone. My assessment, based on the provided documentation is as follows:

(1) Is suggested wording of the Plaque Citation accurate?

Yes, the suggested wording of the Plaque Citation is accurate and effectively summarizes the achievement and its significance. The citation state: "The Sakuma Frequency Converter Station, completed in 1965 by Electric Power Development Co., Ltd., enabled the first large-scale power exchange between Japan' s eastern 50 Hz and western 60 Hz grids via a 300 MW motor-generator frequency converter. This achievement addressed a long-standing national frequency division, improving grid reliability, resilience, and laying the foundation for Japan's future energy interconnection infrastructure." This aligns perfectly with the proposal's abstract, which describes it as "Japan's first large-scale facility to connect the country' s eastern 50 Hz power grid with the western 60 Hz grid" using a "300 MW motor-generator frequency conversion system."

(2) Is evidence presented in the proposal of sufficient substance and accuracy to support the Plaque Citation?

Yes, the evidence presented in the proposal is of sufficient substance and accuracy to support the Plaque Citation. The "Social and Historical Significance" section thoroughly details the historical context of Japan's dual-frequency grid, the immediate technical and operational benefits derived from the Sakuma station, and its long-term impact on the nation's energy infrastructure. Specifically, Reference [1], "Susumu Kuwahara; 'Sakuma Frequency Converter Station', Vol. 85, No. 925, pp.1625-1634, The Journal of the Institute of Electrical Engineers of Japan, 1965," provides contemporary and scholarly confirmation of the station's purpose, capacity (300 MW), and operational time line (completed November 1965). Furthermore, Figure 2, illustrating "Power Interchange 50 Hz/60 Hz on 1965-1983," visually substantiates the claim of large-scale power exchange. The detailed description of "Technical Design and Innovation" and the "Obstacles" section further bolster the proposal's claims with concrete technical details and challenges overcome.

(3) Does proposed milestone represent a significant technical achievement?

Yes, the proposed milestone represents a highly significant technical achievement. The Sakuma Frequency Converter Station, commissioned in 1965, was a pioneering solution to Japan's unique national frequency divide. At its inception, it was "the largest motor-generator-based frequency converter in the world," featuring a "300 MW synchronous motor (50 Hz) directly coupled to a synchronous generator (60 Hz) through a common shaft." This mechanical frequency conversion (MFC) system demanded advanced engineering to ensure "torsional stability, cooling, noise suppression, and control." Key technical innovations included "high-inertia rotors for frequency smoothing, precision excitation control systems for voltage regulation, acoustic insulation for community compatibility, and custom-designed shafts and bearings to withstand continuous mechanical stress at utility scale." The successful design and implementation of such a high-capacity, mechanically coupled system for asynchronous grid interconnection, especially given the lack of precedent in Japan for transferring hundreds of megawatts, marks a profound technical accomplishment.

(4) Were there similar or competing achievements? If so, have the proposers adequately described these and their relationship to the achievement being proposed?

Yes, the proposers have adequately described similar achievements and clearly articulated what sets the Sakuma Frequency Converter Station apart. The "What Features Set This Work Apart from Similar Achievements?" section provides a concise comparison with European HVDC systems (e.g., NorNed, BritNed) and North American asynchronous ties (e.g., Miles City HVDC Tie, Rapid City DC Tie). The proposal correctly highlights that while these systems utilize HVDC for inter-country energy trade or inter-regional asynchronous ties, they do not address a fundamental frequency mismatch within a single industrialized nation, as was the case in Japan. The proposal emphasizes that "Japan is the only industrialized nation with two commercial grid frequencies within one country," necessitating a unique solution like Sakuma. Furthermore, the proposal uniquely positions Sakuma by detailing its "mechanical-to-electronic technological evolution," starting with large-scale synchronous motor-generator sets and later transitioning to a solid-state HVDC back-to-back system in 1993, making it one of the few sites globally to operate under both paradigms of frequency conversion. This comprehensive comparison effectively demonstrates the distinctiveness and national importance of the Sakuma achievement.

(5) Have proposers shown a clear-benefit to humanity?

Yes, the proposers have shown a clear and substantial benefit to humanity. The Sakuma Frequency Converter Station provided a critical solution to a "serious bottle neck" in Japan's power distribution by enabling "meaningful and stable power interchange between the regions for the first time." This significantly enhanced grid flexibility and reliability, leading to tangible benefits such as "reducing the need for regional reserve capacity," "improving frequency stability," and "enabling mutual emergency support, particularly in times of natural disaster, such as earthquakes or typhoons." The proposal cites simulations from the 1960s showing that Sakuma could reduce frequency drops during outages (e.g., a 0.8 Hz drop reduced to 0.4 Hz for a 340 MW loss in Tokyo), directly contributing to a more resilient and responsive national power grid. Its continued operation, especially during emergencies like the 2011 Great East Japan Earthquake, where "west-to-east energy transfer proved vital," underscores its enduring humanitarian impact on energy security and disaster preparedness for the Japanese populace.

Conclusion:
The Sakuma Frequency Converter Station represents an exceptional technical and historical asset. Its pioneering role in bridging Japan's unique dual-frequency power grids, its innovative mechanical frequency conversion technology at an unprecedented scale, and its lasting impact on national energy security and grid resilience make it an outstanding candidate for recognition. The proposal is well-supported with compelling evidence and clearly articulates the achievement's significance and distinctiveness. Therefore, I strongly recommend that the Sakuma Frequency Converter Station be designated as an IEEE Milestone.

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Best Wishes,
Hisao Taoka, Former Professor of Fukui University, IEEE Life Fellow, CIGRE Distinguished Member

Hisao Taoka, Ph. D Engineering Advisor, Power System Solutions Group, Rikei Corporation
Invited Researcher, Energy Network Research Team, Fukushima Renewable Energy Institute, The National Institute of Advanced Industrial Science and Technology (AIST)

[Advocate's remarks_1] Dr. Hisao Taoka is an IEEE Fellow in 2014 for contributions to computing technology for power system analysis and control.

[Advocate's remarks_2] CIGRE is a collaborative global community committed to the world's leading knowledge development program for the creation and sharing of power system expertise. https://www.cigre.org/

Expert Reviewer's Report_3_Nguyen-Van uploaded by Advocate -- Tomohiro Hase (talk) 20:17, 27 July 2025 (UTC)

Dear Prof. Hase,

Please find my review for the Milestone-Proposal: "Sakuma Frequency Converter Station, 1965" below.

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(1) Plaque Citation Accuracy

Yes. The proposed plaque citation is accurate and succinctly captures the essence of the achievement. It correctly identifies the Sakuma Frequency Converter Station as Japan’s first large-scale AC-to-AC interconnection facility, enabling real-time power exchange between the 50 Hz and 60 Hz grids.

(2) Supporting Evidence for Plaque Citation

Yes. The proposal provides substantial and well-documented evidence to support the citation. The “Technical Design and Innovation” section details the station’s architecture, including its use of synchronous motor-generator sets and its 300 MW capacity. The “Social and Historical Significance” section offers relevant context, explaining the origin of Japan’s dual-frequency grid and the societal need for interconnection.

(3) Significance of Technical Achievement

Yes. The Sakuma Frequency Converter Station represents a landmark technical achievement. It was the first facility in Japan to enable large-scale bidirectional power exchange between two asynchronous grids. Its use of high-speed rotating synchronous machines and rapid response capability (300 MW within 1 second) demonstrated advanced engineering and operational reliability. The station laid the groundwork for subsequent interconnection projects, such as Shin-Shinano and Higashi-Shimizu stations.

(4) Similar or Competing Achievements

Yes. The proposal acknowledges later developments, including the Shin-Shinano and Higashi-Shimizu stations, and distinguishes Sakuma’s mechanical AC-to-AC conversion method from HVDC-based systems. While comparable facilities existed abroad, Sakuma holds special significance due to Japan’s unique grid structure. Despite its relatively small geographic area, the creation of a frequency converter station enabling interconnection across asynchronous grids was therefore critical to maximizing its energy infrastructure. The Sakuma station addressed this challenge by adapting and improving upon global technologies, fostering domestic innovation. Its successful implementation exemplified both technical ingenuity and international collaboration.

(5) Benefit to Humanity

Yes. The Sakuma station has delivered lasting societal benefits. It enhanced grid stability, enabled nationwide load balancing, and bolstered disaster resilience—most notably during the 2011 Great East Japan Earthquake. By facilitating efficient energy distribution, it contributed to Japan’s postwar recovery and sustained economic growth. Its continued operation attests to its enduring value and engineering quality.

Conclusion
The Sakuma Frequency Converter Station is a historically and technically significant achievement. It bridged a century-old infrastructural divide and enabled Japan to operate a more unified and resilient power system. Given its pioneering role, long-term impact, and ongoing relevance, I strongly support its recognition as an IEEE Milestone.

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Sincerely,

Triet Nguyen-Van, Ph. D.
Control and Power Systems Lab., Department of Intelligent Interaction Technologies, University of Tsukuba

Appreciation of Submitted Reviews -- Zephyrus00jp (talk) 23:26, 28 July 2025 (UTC)

Hello,

This is Chiaki Ishikawa, one of the proposers.
I would like to thank the reviewers for the reviewes posted here in the last few days.
We will study the reviews and see if there are places where we can improve the proposal.
Thank you again for talking the time to read and write the reviews.

Sincerely,
Chiaki Ishikawa

Expert Reviewer's Report_4_Nagao uploaded by Advocate -- Tomohiro Hase (talk) 01:40, 1 August 2025 (UTC)

Here is an expert review report from prof. Nagao

Media:Review Report_Nagao.pdf

[Advocate's remarks] Dr. Masayuki NAGAO
Emeritus Professor, Toyohashi University of Technology, JAPAN
CIGRE Distinguished Member