106:, each of which has two windings: a control winding and an AC winding. Another common design uses a single core shaped like the number "8" with one control winding and two AC windings as shown in the photo above. A small DC current from a low-impedance source is fed into the control winding. The AC windings may be connected either in series or in parallel, the configurations resulting in different types of mag amps. The amount of control current fed into the control winding sets the point in the AC winding waveform at which either core will saturate. In saturation, the AC winding on the saturated core will go from a high-impedance state ("off") into a very low-impedance state ("on") – that is, the control current controls the point at which voltage the mag amp switches "on".
241:-technique. The current to be measured is passed through the two cores, possibly by a solid bus bar. There is almost no voltage drop in this bus bar. The output signal, proportional to the ampere turns in the control current bus bar, is derived from the alternating excitation voltage of the magnetic amplifier, there is no voltage created or induced on the bus bar. The output signal has only a magnetic connection with the bus bar so the bus may be, quite safely, at any (
383:
75:
27:
374:
converted by a rotating machine (exciter) to 5 megawatt (MW) level, the excitation power required by a typical 500 MW Power Plant
Turbine Generator Unit. They proved durable and reliable. Many are recorded in service through the mid-1990s and some are still in use at older generating stations, notably in hydroelectric plants operating in northern California.
151:
143:
139:. Solid-state electronic amplifiers can be more compact and efficient than magnetic amplifiers. The bias and feedback windings are not unilateral and may couple energy back from the controlled circuit into the control circuit. This complicates the design of multistage amplifiers when compared with electronic devices.
352:
placed an order for a high frequency rotary mechanical alternator from the
General Electric Company capable of generate AC at a frequency of 100 kHz to be used for continuous wave radio transmission over great distances. The design job was given to General Electric engineer Ernst F. Alexanderson
233:
passed through the core of the device. During normal operation the resultant flux was zero as both currents were the same and in opposite directions. The currents would differ during wheel slip, producing a resultant flux that acted as the
Control winding, developing a voltage across a resistor in
187:
or to vary the signal for voice modulation. The alternator's frequency limits were rather low to where a frequency multiplier had to be utilized to generate higher radio frequencies than the alternator was capable of producing. Even so, early magnetic amplifiers incorporating powdered-iron cores
112:
Two magnetic cores are used because the AC current will generate high voltage in the control windings. By connecting them in opposite phase, the two cancel each other, so that no current is induced in the control circuit. The alternate design shown above with the "8" shaped core accomplishes this
398:
designed and produced several high quality high-powered audio amplifiers, calling them magnetic amplifiers. In fact, they were in most respects conventional audio amplifier designs with unusual power supply circuits. They were not magnetic amplifiers as defined in this article. They should not be
373:
Magnetic amplifiers were extensively used in electricity power generation from the early 1960s onwards. They provided the small signal amplification for generator automatic voltage regulation (AVR) from a small error signal at milliwatt (mW) level to 100 kilowatt (kW) level. This was in turn
288:
computers. Like transistors, mag amps were somewhat smaller than the typical vacuum tube, and had the significant advantage that they were not subject to "burning out" and thus had dramatically lower maintenance requirements. Another advantage is that a single mag amp could be used to sum several
121:
The magnetic amplifier is a static device with no moving parts. It has no wear-out mechanism and has a good tolerance to mechanical shock and vibration. It requires no warm-up time. Multiple isolated signals may be summed by additional control windings on the magnetic cores. The windings of a
134:
The gain available from a single stage is limited and low compared to electronic amplifiers. Frequency response of a high-gain amplifier is limited to about one-tenth the excitation frequency, although this is often mitigated by exciting magnetic amplifiers with currents at higher than
182:
used for radio communications. Magnetic amplifiers were also used to regulate the speed of
Alexanderson alternators to maintain the accuracy of the transmitted radio frequency. Magnetic amplifiers were used to control large high-power alternators by turning them on and off for
542:. … One study devoted to the problem indicates that the major damage to core material suitable for self-saturating magnetic amplifiers consists of loss of loop rectangularity and increased dynamic coercive force. This study was made at a total integrated neutron flux of 2.7 ✕
65:
began to supplant it. The magnetic amplifier has now been largely superseded by the transistor-based amplifier, except in a few safety critical, high-reliability or extremely demanding applications. Combinations of transistor and mag-amp techniques are still used.
255:
made extensive use of the magnetic amplifiers. They were used for the master stable element systems, for slow moving transmission for controlling guns, directors and rangefinders and train and elevation controls. Magnetic amplifiers were used in aircraft systems
293:(ALU) as it could greatly reduce the component count. Custom tubes could do the same, but transistors could not, so the mag amp was able to combine the advantages of tubes and transistors in an era when the latter were expensive and unreliable.
300:. That era was short, lasting from the mid-1950s to about 1960, when new fabrication techniques produced great improvements in transistors and dramatically lowered their cost. Only one large-scale mag amp machine was put into production, the
221:
power supplies often use mag amps for secondary side voltage regulation. Cores designed specifically for switch mode power supplies are currently manufactured by several large electromagnetics companies, including
Metglas and Mag-Inc.
188:
were incapable of producing radio frequencies above approximately 200 kHz. Other core materials, such as ferrite cores and oil-filled transformers, would have to be developed to allow the amplifier to produce higher frequencies.
364:
across the
Atlantic Ocean. The 50 kW alternator was commandeered by the US Navy and put into service in January 1918 and was used until 1920, when a 200 kW generator-alternator set was built and installed.
750:
The use of magnetic forces for amplification is not new; a survey of its history shows that although the device was not known as a magnetic amplifier at the time, it was used in electrical machinery as early as
94:
of the core, a non-linear property of a certain class of transformer cores. For controlled saturation characteristics, the magnetic amplifier employs core materials that have been designed to have a specific
122:
magnetic amplifier have a higher tolerance to momentary overloads than comparable solid-state devices. The magnetic amplifier is also used as a transducer in applications such as current measurement and the
195:
and for advertising signs. Saturable reactor amplifiers were used for control of power to industrial furnaces. Magnetic amplifiers as variable AC voltage controllers have been mostly replaced by
174:
Magnetic amplifiers were important as modulation and control amplifiers in the early development of voice transmission by radio. A magnetic amplifier was used as voice modulator for a 2 kilowatt
217:-based solid-state switches have largely superseded them, though recently there has been some regained interest in using mag amps in compact and reliable switching power supplies. PC
635:
The electronic watchdogs that keep the Triton's powerful nuclear plant operating without a hitch are magnetic amplifiers – almost hundred of them are used for this critical job.
126:. The reactor cores of magnetic amplifiers withstand neutron radiation extremely well. For this special reason magnetic amplifiers have been used in nuclear power applications.
678:
The magnetic amplifier is not new – the principles of the saturable core control were used in electrical machinery as early as 1885 although they were not identified as such.
166:
which replaced them, the magnitude of these harmonics decreases rapidly with frequency so interference with nearby electronic devices such as radio receivers is uncommon.
341:
signal source for a low resistance load such as the control coil of a saturable reactor which amplifies the signal. Thus, in principle, a saturable reactor is already an
360:
The experimental telegraphy and telephony demonstrations made during 1917 attracted the attention of the US Government, especially in light of partial failures in the
567:
597:
109:
A relatively small DC current on the control winding is able to control or switch large AC currents on the AC windings. This results in current amplification.
99:
shape that is highly rectangular, in contrast to the slowly tapering B-H curve of softly saturating core materials that are often used in normal transformers.
237:
Magnetic amplifiers can be used for measuring high DC-voltages without direct connection to the high voltage and are therefore still used in the
983:
357:. By 1916 Alexanderson added a magnetic amplifier to control the transmission of these rotary alternators for transoceanic radio communication.
803:
46:
device for amplifying electrical signals. The magnetic amplifier was invented early in the 20th century, and was used as an alternative to
206:
Small magnetic amplifiers were used for radio tuning indicators, control of small motor and cooling fan speed, control of battery chargers.
524:
Lynn, Gordon E.; Pula, Thaddeus J.; Ringelman, John F.; Timmel, Frederick G. (1960). "Effects on
Nuclear Radiation on Magnetic Materials".
158:
Magnetic amplifiers introduce substantial harmonic distortion to the output waveform consisting entirely of the odd harmonics. Unlike the
31:
A small magnetic amplifier rated at 250 watts and designed to operate on 120 VAC, 60 Hz. The large center winding is the control winding.
1026:
345:, although before 20th century they were used for simple tasks, such as controlling lighting and electrical machinery as early as 1885.
248:
Instrumentation magnetic amplifiers are commonly found on space craft where a clean electromagnetic environment is highly desirable.
61:. The magnetic amplifier was most prominent in power control and low-frequency signal applications from 1947 to about 1957, when the
390:
magnetic audio amplifier, designed by
Swedish engineer Lars Lundahl, utilizes saturable reactors in its final power amplifying stage.
191:
The ability to control large currents with small control power made magnetic amplifiers useful for control of lighting circuits, for
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before development of a system using digital electronics. Magnetic amplifiers were used in stabilizer controls of
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704:. New York: John F. Rider Publisher. p. 1. Library of Congress Catalog Number 60-12440. Archived from
720:
Magnetic amplifiers were developed as early as 1885 in the United States. At that time they were known as
538:
The nature of ferromagnetic materials results in far less damage from nuclear radiation than is done to
313:
290:
91:
146:
Magnetic amplifier output waveform (violet) at about 50% saturation. Input (yellow) is 120 VAC 60 Hz.
987:
906:
86:, but the operating principle is quite different from a transformer – essentially the mag amp is a
260:) before the advent of high reliability semiconductors. They were important in implementing early
809:
349:
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Magnetic
Amplifiers Bibliography: A Supplement to Magnetic Amplifiers, Another Lost Technology
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468:
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304:, but a number of contemporary late-1950s/early-1960s computers used the technology, like the
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Magnetic amplifiers were widely studied during the 1950s as a potential switching element for
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Magnetic amplifiers were used extensively as the switching element in early switched-mode (
102:
The typical magnetic amplifier consists of two physically separate but similar transformer
676:. Washington, D.C.: Bureau of Ships, Department of the Navy. p. 2. NAVSHIPS 900,172.
382:
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764:"Ernst F. Alexanderson, The accomplishments and life of E. F. Alexanderson, 1878–1975"
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813:
788:
Fourteenth Annual
Applied Power Electronics Conference and Exposition, 1999. APEC '99
225:
Magnetic amplifiers were used by locomotives to detect wheel slip, until replaced by
214:
763:
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252:
242:
178:, and magnetic amplifiers were used in the keying circuits of large high-frequency
123:
51:
896:
Oldham, D.T; Schindler, P.B. (1964). "An excitation system for 500MW generators".
74:
26:
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series with the AC winding which was sent to the wheel slip correction circuits.
969:"Topic 7. Magnetic Amplifier Control for Simple, Low-Cost, Secondary Regulation"
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The principles of magnetic amplifiers were applied non linearly to create
837:
Alexanderson, E.F.W. (October 1920). "Transoceanic Radio Communication".
269:
265:
261:
257:
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and were used primarily in electrical machinery and in theater lighting.
317:
78:
A saturable reactor, illustrating the principle of a magnetic amplifier
54:
50:
amplifiers where robustness and high current capacity were required.
672:
Electronics Design and Development Division (May 1954) . "History".
497:. Howard W. Sams photofact publication; FMA-1. Wiley. p. 383.
150:
142:
381:
200:
163:
149:
141:
73:
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Wilson, Thomas G. (1999). "The Evolution of Power Electronics".
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confused with real magnetic audio amplifiers, which also exist.
238:
533:
218:
939:
U.S. Navy Department Staff (2000). Trinkaus, George (ed.).
203:. Magnetic amplifiers are still used in some arc welders.
57:
perfected this type of amplifier, and it was used in the
907:"The Magnetic Amplifier: A Lost Technology of the 1950s"
674:
Magnetic Amplifiers – A Rising Star in Naval Electronics
613:"Magnetic Amplifiers – how they work and what they do"
575:
548:
154:
Magnetic amplifier output waveform frequency spectrum
900:. Trafford Park, Manchester: AEI Turbine-Generators.
736:Kemp, Barron (August 1962). "Magnetic Amplifiers".
591:
561:
268:made use of the technology for the control of its
213:) power supplies, as well as in lighting control.
702:Magnetic Amplifiers – Principles and Applications
289:inputs in a single core, which was useful in the
867:Chute, George M. (1971). "Magnetic Amplifiers".
873:(4th ed.). McGraw-Hill. pp. 344–351.
245:) voltage with respect to the instrumentation.
776:Milestones:Alexanderson Radio Alternator, 1904
8:
921:Magnetic Amplifiers: Another Lost Technology
19:
967:Mammano, Bob; Unitrode Corporation (2001).
438:
436:
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42:(colloquially known as a "mag amp") is an
25:
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229:current transducers. The cables from two
82:Visually a mag amp device may resemble a
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333:A voltage source and a series connected
430:
986:. Butler Winding. 2009. Archived from
18:
7:
997:"The Vacuum Tube's Forgotten Rival"
984:"MAG-AMP Magnetic Amplifiers Intro"
738:Fundamentals of Magnetic Amplifiers
526:Self-saturating Magnetic Amplifiers
905:Trinkaus, George (February 2006).
446:Reference Data for Radio Engineers
369:Usage in electric power generation
14:
443:Westman, H.P. (1968). "Ch. 14".
995:Shirriff, Ken (27 March 2022).
1010:"Homemade Magnetic Amplifiers"
1008:Steiner, Nyle (October 2009).
918:Trinkaus, George, ed. (2000).
16:A type of parametric amplifier
1:
898:Turbine-Generator Engineering
790:. Vol. 1. pp. 3–9.
649:Switching Power Supply Design
647:Pressman, Abraham I. (1997).
197:silicon controlled rectifiers
160:silicon controlled rectifiers
113:same objective magnetically.
449:(5th ed.). H. W. Sams.
353:who developed the 2 kW
298:magnetic digital logic gates
766:. Edison Tech Center. 2014.
1053:
1027:Electromagnetic components
611:Gilmore, Ken (July 1960).
999:. History of Technology.
846:Cheney, Margaret (1981).
740:. H. W. Sams. p. 7.
528:. New York: McGraw-Hill.
24:
852:. Simon & Schuster.
796:10.1109/APEC.1999.749482
870:Electronics in Industry
839:General Electric Review
562:{\displaystyle 10^{18}}
540:semiconductor materials
355:Alexanderson alternator
176:Alexanderson alternator
945:. High Voltage Press.
924:. High Voltage Press.
849:Tesla: Man Out of Time
593:
592:{\displaystyle cm^{2}}
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348:In 1904 radio pioneer
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70:Principle of operation
1032:Electronic amplifiers
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503:2027/pst.000030030824
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337:may be regarded as a
314:English Electric KDF9
291:arithmetic logic unit
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978:. Texas Instruments.
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493:Storm, H.F. (1955).
620:Popular Electronics
495:Magnetic Amplifiers
92:magnetic saturation
21:
722:saturable reactors
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362:transoceanic cable
350:Reginald Fessenden
302:UNIVAC Solid State
280:Usage in computing
270:engine air intakes
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90:. It makes use of
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40:magnetic amplifier
20:Magnetic amplifier
1037:Power electronics
805:978-0-7803-5160-8
335:variable resistor
329:Early development
316:, or the one-off
137:utility frequency
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88:saturable reactor
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1021:Categories
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691:Mali, Paul
630:2014-10-20
473:0672206781
425:References
409:Parametron
274:V2 rockets
185:telegraphy
63:transistor
59:V-2 rocket
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403:See also
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451:ISBN
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239:HVDC
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Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
