Who Invented the Transformer

Historical
by Massimo Guarnieri
56 IEEE INDUSTRIAL ELECTRONICS MAGAZINE ■ DECEMBER 2013
Digital Object Identifier 10.1109/MIE.2013.2283834
Date of publication: 12 December 2013
1932-4529/13/$31.00©2013IEEE
f we were to ask who invented
the transformer, we would obtain
different answers from different
countries. The same would happen if
we asked who conceived the internal
combustion engine, the electric mo-
tor, the telegraph, the telephone, the
radio, the television, or the computer.
This is not surprising because, in sev-
eral cases, the priority of inventions
that occurred almost simultaneously
in different places has been the ob-
ject of long and bitter court trails,
and the final judgments have often
raised criticism among specialists.
However, the transformer evolved
during a time span of about 50 years,
making it possible to identify dif-
ferent stages along which different
inventors provided increasing perfor-
mance, leading the device to assume
its present structure and operational
features.
The merit of discovering mutual
magnetic induction between two
coupled circuits, in 1831, belongs to
the great English physicist and chem-
ist Michael Faraday (1791–1867). Be-
ing the son of a blacksmith, he was
self-taught, thanks to chemistry and
electricity books, which he read dur-
ing his apprenticeship in a bookbind-
er’s shop—a job he started at age 14.
When he was still a teenager, he had
the chance to attend lectures by the
great chemist Humphrey Davy at
the Royal Institution. At age 21, Davy
hired him as an assistant at the Royal
Institution, where Faraday remained
for the next 50 years, having been
appointed superintendent of its labo-
ratory in 1821.
Although the lack of formal educa-
tion left him with mathematical gaps,
these were largely offset by a prodi-
gious experimental intuition that al-
lowed him to become one of the most
influential experimental researchers
of all time. The same year, he began
investigating the interactions between
magnets and currents. He devised
the concept of the line of force (a term
he introduced) for justifying the fig-
ures formed by the iron filings near a
magnet. Using this concept, in August
1831, he discovered mutual magnetic
induction by noting the transient cur-
rent induced in a coil when the current
was turned on and off in a second coil,
both wound on the same toroidal iron
core (Figure 1). In October 1831, he
observed self-induction, as the result
of the current induced in a solenoidal
coil by the movement of a magnet in-
side its bore. Nevertheless this latter
effect had already been discovered by
the less famous Francesco Zantede-
schi (1797–1873) in Italy in 1830 and
by Joseph Henry (1797–1878) in the
United States in 1831. Thus, thanks to
these men, a key and stealth feature
had been finally been found: variable
magnetic fields are needed to obtain
electric effects. These results, which
integrated the discovery of the magnet-
ic effects of electric currents divulged
by Danish physicist and chemist Hans
Christian Ørsted (1777–1851) in 1820,
completed the epistemological frame-
work of quasistationary electromag-
netism. Faraday introduced the term
electromotive force for such an effect,
and we still see this in use today. In
1831, Faraday also built the archetype
of an electromechanical generator. He
introduced the concept of dielectric
constant and built the first variable ca-
pacitor in 1837. He also studied optics
and the polarization of light with his
friend Charles Wheatstone, discover-
ing the Faraday effect (the rotation of
polarized light when passing through
a magnetized region) in 1845. Between
1846 and 1855, he recognized the mag-
netic properties of matter and intro-
duced the concepts of diamagnetism.
By developing the idea of lines
of force, he introduced the notions
of electric and magnetic fields. The
mathematical formulation of electro-
magnetic induction was developed by
German physicist and mathematician
Franz Ernst Neumann (1798–1895),
in 1945. These discoveries paved the
way toward the fundamental theoreti-
cal composition carried out by James
Clerk Maxwell (1831–1879), starting
with “On Faraday’s Lines of Force”
[1], whose “Dynamical Theory of the
Who Invented the Transformer?
I
FIGURE 1 – Faraday coupled coils in 1831.
(Image courtesy of Wikipedia.)
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DECEMBER 2013 ■ IEEE INDUSTRIAL ELECTRONICS MAGAZINE 57
Electromagnetic Field” [2] reported
for the first time the equations of the
mutual inductor as we know today.
However, Maxwell’s work was initially
mistrusted by most physicists and ig-
nored by engineers. Only toward the
end of the 19th century, after the mem-
orable experiment on electromagnetic
waves performed by Heinrich Hertz in
1887, was Maxwell’s theory generally
accepted and allowed to address both
physics and technology. No less im-
portant were Faraday’s discoveries in
chemistry, where he authored several
breakthroughs. He collected his colos-
sal scientific production mainly into
Experimental Researches, published in
several issues between 1839 and 1855.
He delivered memorable lecturers at
the Royal Institution, was appointed
a Fellow of the Royal Society in 1824,
and received the Copley Medal twice,
in 1832 and 1838, but refused the noble
title and the presidency of the Royal
Institution (1864) and did not want to
register any patent.
However, the transformer has a
fundamental feature that Faraday
missed, namely, the capacity to trans-
form the generator’s voltage and
current to adapt them to the load re-
quirements. From this point of view,
it is inappropriate to deem him as
the transformer’s inventor. We must
consider that, at that time, the avail-
able generators were batteries, i.e.,
direct current (dc) devices, so that
the variation of mutually linked in-
duction needed by the transformer
would rely on some commutation
technology. The man who first caught
on to the idea was an Irish clergy-
man, Nicholas Joseph
Callan (1799–1864). After
being ordained, he stud-
ied physics at the Uni-
versity of Rome, where
he graduated in 1826. On
his return to Ireland, he
was appointed profes-
sor of natural philosophy
(which we now call phys-
ics) at St. Patrick’s College
in Maynooth, not far from
Dublin, where he started
his laboratory. In 1836,
he built the first device
capable of exploiting ef-
ficiently the mutual cou-
pling. It consisted of two
coils, one of few turns and
one of many well-isolated turns, both
wound on an iron core (Figure 2).
Abrupt termination of the current of
the first coil induced a high voltage in
the second (possibly as high as some
tens of kilovolts). In 1854–1855, he
developed electrochemical cells that
he assembled in large batteries to
power electromagnets capable of de-
veloping forces as high as two tons.
He also built early electric motors and
patented an electroplating process,
aimed at preventing iron oxidation, in
1853. Nonetheless, he did not neglect
his religious vocation, writing about
20 books on such topics.
Callan built his device because he
needed high voltages in his experi-
ments, transforming them from low
voltage provided by his batteries, but
he failed to take it to broad exploita-
tion. Instead, in 1851,
Heinrich Daniel Ruhm-
korff (1803–1877) pat-
ented it and took it to
broad use, so it became
famous as the “Ruhm-
korff coil” ( Figure 3).
Several other inventors
were working on its im-
provement, introducing
a “divided” iron core to
reduce losses and au-
tomatic interrupters.
Ruhmkorff was a Ger-
man instrument maker
who moved abroad for
work, first to England
and t hen to France.
I n Paris, he started a
workshop to produce scientific instru-
ments. The voltage induced in his 1851
secondary coil could start sparks of
5 cm, but in his improved model of
1857 they could reach 30 cm. These de-
vices assured Ruhmkorff with success:
Napoleon III awarded him a prize of
50,000 francs in 1858. He also invented
other implements, such as the Ruhm-
korff lamp, which included his coil, and
a thermoelectric battery.
FIGURE 2 – The first induction coil built by
Nicholas Callan in 1836. (Image courtesy of
Wikipedia.)
FIGURE 3 – The induction coil by Ruhmkorff in 1850. In addition to the hammer interrupter
(right), it had a mercury interrupter by Fizeau (left) that could be adjusted to change the dwell
time. (Image courtesy of Wikipedia.)
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THE TRANSFORMER
HAS A
FUNDAMENTAL
FEATURE THAT
FARADAY MISSED,
NAMELY, THE
CAPACITY TO
TRANSFORM THE
GENERATOR’S
VOLTAGE AND
CURRENT TO ADAPT
THEM TO THE LOAD
REQUIREMENTS.
58 IEEE INDUSTRIAL ELECTRONICS MAGAZINE ■ DECEMBER 2013
In the following years, the Ruhm-
korff coil was used in telegraphy and
played a fundamental role in experi-
mental research as a source of high
voltages more efficient than contem-
porary electrostatic machines. From
1861, it was used by English physi-
cist and chemist William Crookes
(1832–1919) to power his vacuum
tubes, which he used to perform early
experiments on cathode
rays. His results led him
to propose that they con-
sisted of particles with
a negative charge (the
very early intuition of the
electron). Research using
similar devices brought
to light the concept of
X-rays (produced by the
impact of the cathode ray
on a target), which were
systematically studied by
the German physicist Wilhelm Conrad
Röntgen (1845–1923) from 1895.
Röntgen was awarded the first Nobel
Prize in physics for these achieve-
ments. British physicist Joseph John
“J.J.” Thomson (1856–1940), another
Nobel laureate (1906), used the device
in further experiments, which led him
to discover the electron, recognizing
it to be a thousand times lighter than
the hydrogen atom, in 1897. This re-
sult had been anticipated in 1895 by
the French physicist Jean-Baptiste Per-
rin (1870–1942), after his experiments
with similar equipment. Perrin was
also awarded the Nobel Prize in phys-
ics, in 1926.
All of these experimental devices
used the transformer introduced
by Callan to produce repeated high-
voltage pulses, being
powered by dc batteries.
Only dc was widespread
at that time [3]. How-
ever, in 1876, a simple,
cheap, and efficient arc
lamp had appeared—the
Jabl ochkov candl e—
that soon gained great
success in Europe and
America. To ensure equal
consumption of the two
paral l el carbon rods
among which the arc was established,
the current had to be continuously
reversed, and to this aim, producers
such as Gramme in France started to
build alternators derived from their
dc dynamos. Alternating current (ac)
technology was emerging.
The idea of applying coupled coils
to ac systems was first conceived by
Jablochkov, the inventor of the candle,
but it passed unobserved. Instead, it
was first realized in London in 1881
by French chemist Lucien Gaulard
(1850–1888) and British John Dixon
Gibbs (1834–1912) [3]. Their device,
derived from the Ruhmkorff coil and
dubbed the secondary generator, had
a 1:1 turn-ratio and an open iron core
(Figure 4). Several such devices were
fed at their primaries connected in
series, while their secondaries fed in-
dependent users at low voltage. They
patented and demonstrated it in Lon-
don in 1882 and again at the Turin In-
ternational Exhibition of 1884 on an
ac line extending a record distance
of 34 km. That same year, Italian en-
gineer Galileo Ferraris (1847–1897),
the organizer of the Turin exhibition,
developed the first theoretical inves-
tigation of the device, highlighting its
high efficiency. In 1886, Gaulard de-
veloped an improved version of his
secondary generator, with a closed
iron core. However, he had been pre-
ceded by Hungarian engineer Ottó Ti-
tusz Bláthy (1860–1939) of Ganz & Co.,
Budapest, who, in 1885, had built the
first transformer with a toroidal closed
core; moreover, Bláthy was the first to
dub the device with its present name
(Figure 5). The company, already op-
erating in the railway industry, had
entered the electric sector in 1878
and four years later was able to pro-
duce good alternators designed by
Károly Zipernowsky (1853–1942) and
Miska Déri (1854–1938). In 1885, the
three men developed the ZBD system
(named from their initials), where
step-down transformers had their
primaries shunt connected to a high-
voltage line to feed low-voltage loads
connected to their secondaries [4].
This was a major improvement since
it allowed secondary voltages to be
almost independent of load condi-
tions. Thanks to this technology, Ganz
emerged as one of the foremost elec-
tric companies in Europe.
The fate of Gaulard, the father of
the ac transformer, was not so lucky.
The potential of his invention was not
recognized immediately in France, and
his patent was opposed by Sebastian
Ziani de Ferranti (1864–1930) in Great
Britain. He fell victim to a deep de-
pression, was hospitalized, and died
shortly afterwards.
In America, the pioneer of the
transformer was William Stanley, Jr.
(1858–1916), an engineer of West-
inghouse Electric Company, who in
1886 improved Bláthy’s device with
a laminated core, allowing cheaper
construction and better insulation,
FIGURE 4 – A secondary generator by Lucien
Gaulard, 1881. (Photo courtesy of Museo
Galileo, Firenze, Italy.)
FIGURE 5 – A transformer by Ottó Titusz
Bláthy, 1885. (Photo courtesy of Museo della
Tecnica Elettrica, Università di Pavia, Italy.)
IN AMERICA, THE
PIONEER OF THE
TRANSFORMER WAS
WILLIAM STANLEY,
JR. (1858–1916),
AN ENGINEER OF
WESTINGHOUSE
ELECTRIC COMPANY.
DECEMBER 2013 ■ IEEE INDUSTRIAL ELECTRONICS MAGAZINE 59
suitable for higher voltages. The
same year, he put the first American
ac system into service in Barrington,
Massachusetts. It powered incandes-
cent lamp lighting and was based on
the ZBD concept, but also used step-
up transformers for the first time. In
1890, he started his own transformer
factory, which in 1903 was acquired
by General Electric. In 1893, he pro-
vided the first three-phase transform-
ers to the first American polyphase
power station at Redlands, Califor-
nia. For his achievement, he is often
deemed in American literature as the
person who built the first modern
transformer. He also invented a coun-
ter for ac and an incandescent lamp
with a carbonized silk filament. He
registered 129 patents.
A further step ahead in America was
made in 1887 by British-born chemist
and electrician Elihu Thomson (1853–
1937). A former high school teacher,
in 1880 together with Prof. Edward
J. Houston (1847–1914), he founded
the American Electric Company (later
Thomson-Houston Electric Company),
to produce systems for arc lighting,
which met with great success. In 1886,
they started producing ac systems for
incandescent lighting, and, working on
this line, Thomson in 1887 built the first
oil-insulated transformer, capable of
better insulation and cooling. In 1888,
he conceived the constant-current
transformer and the elec-
tric resistance welding,
which allowed previously
impossible welding op-
erations. The invention
was exploited by a new
company, Thomson Elec-
tric Welding. In 1892, he
promoted the merger of
Thomson-Houston Elec-
tric Company and Edison
General Electric Com-
pany, giving life to the
General Electric Company
(GE). He led the company
research laboratory, the
Thomson Laboratory,
where he developed
traction motors, electric
meters, protection devices, X-ray ma-
chines, and three-phase alternators. He
registered nearly 700 patents and was
a founding member of the International
Electrotechnical Commission and the
president of the Massachusetts Insti-
tute of Technology from 1920 to 1923.
Furthermore, Nikola Tesla (1856–
1943), the Serbian-born American
inventor, father of the induction mo-
tor, American polyphase systems,
radio equipment, and other electri-
cal innovations, conceived his own
transformer in 1891.
This was the Tesla coil,
consisting of two weakly
coupled coils with air
core, both resonant at
the same high frequency
and able to produce ex-
tremely high voltages
(millions of volts), which
he used in spectacular
experiments, generating
lightning bolts as long
as several meters (Fig-
ure 6). After decades of
neglect, this concept is
now attracting the atten-
tion of a growing number
of researchers as it is the
basis of midrange wire-
less power supply.
Now the transformer has evolved
to a new age. Our portable devices
(smartphones, tablets, laptops, etc.) are
recharged by electronic transformers
that we carry with us and use around
the world, regardless of voltages and
frequencies. In these small devices,
magnetic induction has given way to
solid-state electronics, and a similar
evolution seems to be at the door in
power applications, with the concept
of solid-state transformers, which are
expected to provide much more flex-
ible operations, including energy stor-
age and dc operation and connection.
There are reasons to think that the list
of names associated with “the inven-
tor of the transformer” will be extend-
ed in the near future.
References
[1] J. C. Maxwell, “On Faraday’s lines of force,”
Trans. Cambridge Philosophical Society, vol. 10,
part I, pp. 155–209, 1855–6.
[2] J. C. Maxwell, “Dynamical theory of the elec-
tromagnetic field,” Philosophical Trans. Royal
Society of London, vol. 155, pp. 459–512, 1864.
[3] M. Guarnieri, “The beginning of electric ener-
gy transmission: Part one,” IEEE Ind. Electron.
Mag., vol. 7, no. 1, pp. 50–52, 2013.
[4] M. Guarnieri, “The beginning of electric ener-
gy transmission: Part two,” IEEE Ind. Electron.
Mag., vol. 7, no. 2, pp. 52–59, 2013.

FIGURE 6 – Nikola Tesla sitting close to a Tesla coil producing long sparks in his Colorado
Springs Laboratory, 1899. (Image courtesy of Wikimedia Commons.)
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THIS WAS THE TESLA
COIL, CONSISTING
OF TWO WEAKLY
COUPLED COILS
WITH AIR CORE,
BOTH RESONANT
AT THE SAME HIGH
FREQUENCY AND
ABLE TO PRODUCE
EXTREMELY
HIGH VOLTAGES
(MILLIONS
OF VOLTS).