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This Proposal has been approved, and is now a Milestone
To the proposer’s knowledge, is this achievement subject to litigation? No
Is the achievement you are proposing more than 25 years old? Yes
Is the achievement you are proposing within IEEE’s designated fields as defined by IEEE Bylaw I-104.11, namely: Engineering, Computer Sciences and Information Technology, Physical Sciences, Biological and Medical Sciences, Mathematics, Technical Communications, Education, Management, and Law and Policy. Yes
Did the achievement provide a meaningful benefit for humanity? Yes
Was it of at least regional importance? Yes
Has an IEEE Organizational Unit agreed to pay for the milestone plaque(s)? Yes
Has an IEEE Organizational Unit agreed to arrange the dedication ceremony? Yes
Has the IEEE Section in which the milestone is located agreed to take responsibility for the plaque after it is dedicated? Yes
Has the owner of the site agreed to have it designated as an IEEE Milestone? Yes
Year or range of years in which the achievement occurred:
Title of the proposed milestone:
The Silicon Controlled Rectifier (SCR)/Thyristor 1957
Plaque citation summarizing the achievement and its significance:
The three-terminal p-n-p-n device introduced by General Electric (GE) in 1957 as the silicon controlled recifier (SCR, later thyristor) became the dominant control device in the power industry. The development of the SCR revolutionized the control of electrical machines. Prior to 1955, triode vacuum tubes were used fro machine control that were difficult to operate and were notoriously unreliable. The symmetrical switch (TRIAC) evolved from the SCR, later still came the gate turn-turn-off thyristor.
In what IEEE section(s) does it reside?
Schenectady, New York
IEEE Organizational Unit(s) which have agreed to sponsor the Milestone:
IEEE Organizational Unit(s) paying for milestone plaque(s):
Unit: Power Electronics Society
Senior Officer Name: Alan Mantooth, President
IEEE Organizational Unit(s) arranging the dedication ceremony:
Unit: Power Electronics Society
Senior Officer Name: Alan Mantooth, President
IEEE section(s) monitoring the plaque(s):
IEEE Section: Schenectady, New York
IEEE Section Chair name: Amal Mallavarapu
Proposer name: W.G. Hurley
Proposer email: Proposer's email masked to public
Please note: your email address and contact information will be masked on the website for privacy reasons. Only IEEE History Center Staff will be able to view the email address.
Street address(es) and GPS coordinates of the intended milestone plaque site(s):
Museum of Science and Innovation 15 Nott Terrace Heights Schenectady, NY 12308 U.S.A.
Describe briefly the intended site(s) of the milestone plaque(s). The intended site(s) must have a direct connection with the achievement (e.g. where developed, invented, tested, demonstrated, installed, or operated, etc.). A museum where a device or example of the technology is displayed, or the university where the inventor studied, are not, in themselves, sufficient connection for a milestone plaque.
Please give the address(es) of the plaque site(s) (GPS coordinates if you have them). Also please give the details of the mounting, i.e. on the outside of the building, in the ground floor entrance hall, on a plinth on the grounds, etc. If visitors to the plaque site will need to go through security, or make an appointment, please give the contact information visitors will need. The Museum of Science and Innovation has custody of the GE Heritage Museum
The General Electric Photograph collection consists of nearly 1.5 million images dating from 1891-1960 and depicts the development of the electrical industry and 20th century American life. The images document almost every aspect of the company, including product installations, advertising, consumer and industrial products, factories, executives, researchers, and factory workers
Are the original buildings extant?
The original buildings where the SCR was developed is no longer there.
Details of the plaque mounting:
In the lobby of the Museum
How is the site protected/secured, and in what ways is it accessible to the public?
The Plaque will be visible to the public in the lobby of the Museum. There will be an exhibition of materials related to the SCR/Thyristor in the Museum itself
Who is the present owner of the site(s)?
Museum of Science and Innovation, Schenectady
What is the historical significance of the work (its technological, scientific, or social importance)?
The invention of the SCR/Thyristor revolutionized the control of power conversion by replacing vacuum tube mercury-arc controlled rectifier (the thyratron) with a three terminal semiconductor device. It is a four layer three terminal solid state semiconductor device. It has an anode, a cathode and a gate. The diode is a two terminal device, current flows from the anode to the cathode when a positive voltage is applied betweent the anode and the cathode. The SCR operates like a diode except that current cannot flow until a small voltage is applied between the gate and the cathode. Current flow is stopped by reducing the current below the latching value.
The breakthrough in the invention of the SCR/Thyristor led to dramatic improvements in the rectification of line voltages and was the basis of modern speed control of ac and dc motors.
The initial appication for the SCR was in phased controlled rectification. Rectification involves the conversion of ac voltage to dc voltage. Phase controlled rectification allowed ac voltage to be converted to dc voltage and by delaying the trigger point the average value of the dc output can be regulated. This led to the rapid developmento of high voltage dc transmission for long distances and for undersea transmission.
What obstacles (technical, political, geographic) needed to be overcome?
Phase control was well established in the first half of the twentieth century but the implementation using gas-discharge devices was unreliable and involved complex circuitry. The SCR was both reliable and led to easy implementation in simplifeid circuits. Switching circuits by their nature had lower losses than linear ciruits that involved continuous dissipation. As an example a transistor in continuous operation could regulate the power transfer in a circuit by the princilple of maximum power transfer but the dissipation meant that the circuit was very inefficient, switching solved this by limiting the losses in the circuit to the switching operation.
Transistors had been around for nearly a decade but they opearted in a linear mode. There was a lack of suitable materials to add an additional semiconductor layer to the transistor until the SCR arrived on the scene.
What features set this work apart from similar achievements?
The invention of the SCR was unique in the history of power electronics. Achievements in the decade prior to the invention of the SCR mainly realted to the three terminal transistor, the point contact transistor at Bell Telephone Laboratories (BTL). This led to the profusion of applications for the transistor that operated in continuous conduction and wasn't suitable for switching circuits. It is the efficiency of the switching circuits that sets the SCR apart.
The development of the mercury arc valve for dc transmisison continued into the 1960's until the voltage and current ratings of the SCR reached those of the competing vacuum valves.
Supporting texts and citations to establish the dates, location, and importance of the achievement: Minimum of five (5), but as many as needed to support the milestone, such as patents, contemporary newspaper articles, journal articles, or chapters in scholarly books. 'Scholarly' is defined as peer-reviewed, with references, and published. You must supply the texts or excerpts themselves, not just the references. At least one of the references must be from a scholarly book or journal article. All supporting materials must be in English, or accompanied by an English translation.
 SCR Is 50 Years Old, E. L. Owen , IEEE Industry Applications Magazine, Volume 13, Issue 6, Pages 6 - 10, 2007
 The Silicon p-n-p-n Switch and Sontrolled Rectifier (Thyristor), N. Holonyak, IEEE Transactions on Power Electronics, Volume 16, Issue 1 Pages 8 - 16, 2001
 dc Power Transmission: Mercury-Arc to Thyristor HVdc Valves, Deepak Tiku, IEEE Power and Energy Magazine, Volume 12, Issue: 2 Pages: 76 - 96, 2014
 Fiftieth anniversary of modern power electronics: The Silicon Controlled Rectifier, E. L. Owen, IEEE Conference on the History of Electric Power , Pages 201 - 211, 2007
 GE SCR Manual, 5th Ed., GE Syracuse New York, 1972
Supporting materials (supported formats: GIF, JPEG, PNG, PDF, DOC): All supporting materials must be in English, or if not in English, accompanied by an English translation. You must supply the texts or excerpts themselves, not just the references. For documents that are copyright-encumbered, or which you do not have rights to post, email the documents themselves to email@example.com. Please see the Milestone Program Guidelines for more information.
Please email a jpeg or PDF a letter in English, or with English translation, from the site owner(s) giving permission to place IEEE milestone plaque on the property, and a letter (or forwarded email) from the appropriate Section Chair supporting the Milestone application to firstname.lastname@example.org with the subject line "Attention: Milestone Administrator." Note that there are multiple texts of the letter depending on whether an IEEE organizational unit other than the section will be paying for the plaque(s).