The history
Nearly two centuries from Faraday's iron ring to the 1,200 kV giants tested in Madhya Pradesh.
In 1831 Michael Faraday wound two coils on an iron ring and found that switching one on made a current flicker in the other. Fifty years later inventors in London, Budapest and Massachusetts turned that trick into a machine that could change AC voltage at will, and alternating current won the race to power the world. Since then transformers have grown to hundreds of megavolt-amperes, their cores have become thinner and cleverer, and India has built its own, from Bhopal to the 1,200 kV test station at Bina.
1831
Two coils on one iron ring
Michael Faraday, England
1881–82
Transformer-based AC distribution shown
Lucien Gaulard and John Dixon Gibbs, London
1885
Closed-core transformers in parallel; the word “transformer”
Zipernowsky, Bláthy and Déri, Budapest
1886
Complete step-up and step-down AC system in the USA
William Stanley Jr., Great Barrington
1891
Long-distance three-phase line
Lauffen to Frankfurt, Germany
1902
Long high-voltage line in India
Sivasamudram to Kolar Gold Fields
1921
Buchholz gas relay
Max Buchholz, Germany
2012
India's first 1,200 kV transformer
BHEL, Bhopal
1820 – 1882
Electricity makes magnetism, and changing magnetism makes electricity. Two coils on one ring become the first transformer, though no one calls it that yet.
1820
During a lecture, Ørsted noticed that a wire carrying current made a nearby compass needle swing. He published the result in July 1820. It was the first proof that electricity and magnetism are linked.
Why it mattered. If a current makes magnetism, people began to ask whether magnetism could make a current.
1831
29 August 1831
Faraday wound two separate coils of wire on an iron ring. When he connected a battery to one coil, a needle connected to the other coil flicked, then fell back. It flicked again, the other way, when he disconnected. A current appeared only while the magnetism was changing.
Why it mattered. This ring was, in effect, the first transformer: two coils sharing one iron core.
1832
1831–1832
Working separately, the American Joseph Henry also found that a changing current in one coil induces a current in another, and he discovered self-induction. Faraday published first, so the law carries his name.
Why it mattered. Two independent discoveries showed induction was a real, repeatable effect of nature.
1836
Callan wound a short primary of thick wire and a long secondary of thin wire on an iron core, and broke the primary current rapidly. The secondary gave sparks of very high voltage. Induction coils like his were used for decades in labs, and later for X-rays and car ignition.
Why it mattered. It showed that more turns on the secondary means a higher voltage: stepping up.
1881 – 1890
Gaulard and Gibbs, then the Ganz engineers in Budapest and William Stanley in America, build practical transformers that let one AC line feed many lamps at a safe voltage.
1882
1881–1882
The Frenchman Gaulard and the Englishman Gibbs showed a device they called a secondary generator: coils on an open iron core that lowered an AC voltage for lamps. Their coils were connected in series along the line, which made each lamp affect the others.
Why it mattered. It was the first system to use induction coils to distribute electricity at a different voltage from the line.
1884
For the International Exhibition of Electricity in Turin, Gaulard's system ran a line about 34 km long, fed by a 2,000 V, 130 Hz Siemens & Halske alternator. It worked well and was taken up for electric lighting.
Why it mattered. It proved AC with transformers could carry power over tens of kilometres.
1885
1884–1885
Three engineers at the Ganz works built transformers with a closed iron core, so almost all the flux linked both coils, and connected them in parallel across the line. They filed their patents between January and March 1885. Bláthy is credited with coining the name “transformer”.
Why it mattered. Closed cores and parallel connection are how every power transformer has worked since.
1885
1 May 1885
At the Hungarian National Exhibition, a 1,350 V AC generator fed 75 ZBD transformers connected in parallel. Together they lit 1,067 lamps of 60 V.
Why it mattered. It was the first public show of a practical transformer distribution system.
1886
20 March 1886
Stanley stepped a 500 V generator's output up to 3,000 V, sent it along wires strung on the elm trees of Main Street, and stepped it down again. Transformers in the basements of shops and offices fed their lamps at about 100 V.
Why it mattered. It was the first complete AC system in the USA with step-up and step-down transformers, now an IEEE Milestone.
1886 – 1935
The war of the currents ends in AC's favour. Three-phase lines run for hundreds of kilometres, and India builds some of the earliest long high-voltage lines.
1888
1888–1893
Edison's companies sold low-voltage DC, which could only reach a kilometre or two from a power station. Westinghouse sold AC, which transformers could step up for long lines. Westinghouse bought Tesla's AC motor patents in 1888, and after a bitter public fight his company won the contract to light the 1893 World's Columbian Exposition in Chicago.
Why it mattered. The transformer was AC's winning card: DC had no simple way to change voltage.
1891
1889–1891
Dolivo-Dobrovolsky developed three-phase generators, motors and transformers at AEG. In 1891 a 15 kV three-phase line about 175 km long carried power from a hydro plant at Lauffen to the electrical exhibition in Frankfurt.
Why it mattered. It showed that three-phase AC, with transformers at each end, could move power across a country.
1896
16 November 1896
AC from the new hydroelectric plant at Niagara Falls was stepped up and sent about 40 km to the city of Buffalo. More lines and more customers followed.
Why it mattered. It confirmed AC and transformers as the way to build large power systems.
1897
10 November 1897
The Sidrapong hydel station near Darjeeling began with two 65 kW generators to light the hill town. It was later expanded to about 1,000 kW and still stands.
Why it mattered. It began India's story of generating and distributing electricity.
1902
30 June 1902
A hydro plant at the Kaveri falls sent power about 147 km to the gold mines at Kolar. Transformers raised the voltage to around 30,000–35,000 V for the journey and lowered it again at the mines. It was among the longest high-voltage lines in the world at the time.
Why it mattered. It was India's first long-distance high-voltage line, and it later brought electric light to Bengaluru.
1915
Tata's hydro station at Khopoli in the Western Ghats started sending power over high-voltage lines to Bombay's textile mills.
Why it mattered. It showed Indian industry could run on power made far away and carried by transformers and lines.
1890 – 1990
Oil cooling, silicon steel, grain-oriented steel, the Buchholz relay and glassy amorphous metal make transformers cooler, safer and far less wasteful.
1891
1891 (patent filed)
Early transformers were cooled by air and insulated with cloth and shellac. In a patent filed on 28 August 1891, Elihu Thomson of the Thomson-Houston company described transformers that could be enclosed in oil. Oil-filled tanks soon became the usual design for larger units.
Why it mattered. Oil insulates far better than air and carries heat away, so transformers could be made bigger and more compact at once.
1900
c. 1900
Hadfield had made iron alloyed with silicon in the 1880s. Around 1900, he and the physicist William Barrett reported that it has much lower magnetic losses than plain iron. Silicon steel soon replaced iron in transformer cores.
Why it mattered. Silicon raises the steel's resistance, weakening eddy currents, so cores wasted much less energy.
1921
Buchholz, a senior official at the Prussian electricity company, studied damaged transformers and saw that internal arcs break the oil down into gas. He designed a relay for the pipe to the conservator that collects that gas to raise an alarm, and trips the transformer on a sudden surge of oil.
Why it mattered. It gave oil-filled transformers an early warning of faults inside, and it is still fitted today.
1934
Goss patented a way of rolling and annealing silicon steel so its crystals line up along the sheet. Flux flows far more easily in that direction. This cold-rolled grain-oriented (CRGO) steel became the standard for power transformer cores.
Why it mattered. CRGO cut core losses sharply, and almost every large transformer core still uses it.
1982
late 1970s–1980s
Metals cooled so fast that they freeze without crystals can be magnetised with very little loss. Ribbons of this amorphous metal, about 0.025 mm thick, were made into transformer cores from the late 1970s, and US utilities installed hundreds of thousands of amorphous-core distribution transformers.
Why it mattered. They cut no-load losses by around 70 per cent, and India now uses them too.
1936 – today
Line voltages climb from 287 kV to 1,150 kV. India runs 765 kV lines, tests 1,200 kV, and tightens the efficiency rules for its street transformers.
1936
9 October 1936
A 287.5 kV line about 428 km (266 miles) long began carrying power from Hoover Dam to Los Angeles, the highest transmission voltage of its day.
Why it mattered. Higher voltage let distant dams feed growing cities.
1952
Sweden opened the world's first 380 kV AC line, running about 1,000 km from hydro plants in the far north towards the south.
Why it mattered. 380–400 kV became the backbone voltage of grids across Europe and, later, India.
1965
29 November 1965
Hydro-Québec switched on the world's first 735 kV line, bringing hydropower about 600 km south to Montréal.
Why it mattered. It opened the era of extra-high-voltage transmission, now an IEEE Milestone.
1985
July 1985
A 432 km line in Kazakhstan was commissioned at 1,150 kV, still the highest AC voltage ever used in regular service. After 1991 it was run at 500 kV.
Why it mattered. It showed the limits of AC transmission, and the huge transformers such lines need.
2007
c. 2007
POWERGRID's 351 km Sipat–Seoni line and its 765/400 kV substation at Seoni brought 765 kV transmission to India. 765 kV corridors now link coal, hydro and solar regions to distant cities.
Why it mattered. One 765 kV line carries as much power as several 400 kV lines on less land.
2012
February 2012
A 333 MVA, 1,150/400/33 kV single-phase transformer designed and built by BHEL in Bhopal energised the 1,200 kV National Test Station at Bina, set up by POWERGRID with Indian manufacturers. A second phase was charged in 2016.
Why it mattered. India joined the few countries able to build ultra-high-voltage AC equipment.
2017
1 January 2017
BEE's revised star labelling for distribution transformers took effect, extending the scheme to 11 kV units up to 2,500 kVA and lowering the allowed losses: the old 4 and 5 stars became the new 1 and 2. The limits line up with the energy-efficiency levels of the BIS standard IS 1180.
Why it mattered. With millions of transformers humming day and night, small cuts in loss save a great deal of energy.
By the numbers
Each point is a record line from the history above. Voltage rose about 500 times in a century, which cut the current, and the I²R loss, for the same power.
1956 – 2013
BHEL starts making heavy electrical equipment in Bhopal, then transformers in Jhansi, and India's grid grows into one national network.
1956
1956–1960
India set up Heavy Electricals (India) Limited on 29 August 1956, with help from Associated Electrical Industries of Britain. Its Bhopal factory, which makes transformers among other equipment, was dedicated to the nation in November 1960. Bharat Heavy Electricals Limited was formed in 1964.
Why it mattered. India began making its own power transformers instead of importing them.
2013
31 December 2013
The 765 kV Raichur–Solapur line synchronised the southern grid with the rest of India, making one national grid running at one frequency.
Why it mattered. Power can now flow from any region to any other, through transformers at every step.
Did you know?
The name “transformer” comes from the Ganz engineers in Budapest in 1885; Ottó Bláthy is usually credited with it.
Transformers hum at 100 Hz in India, twice the mains frequency: the core's steel stretches very slightly on every half-cycle, whichever way the flux points.
Eddy-current loss grows with the square of the lamination thickness, which is why core sheets are only about a quarter of a millimetre thick.
Paper insulation ages about twice as fast for every 6 °C above 98 °C, so a transformer's life depends on how hot its hottest spot gets.
On 30 and 31 July 2012, grid failures in north and east India left more than 600 million people without power.
The people
1791 – 1867 · Physicist and chemist · England
Discovered electromagnetic induction with two coils on an iron ring.
1850 – 1888 · Inventor · France
With Gibbs, built the first transformer system for distributing AC lighting.
1834 – 1912 · Engineer and financier · England
Gaulard's partner, who backed and co-patented the secondary generator.
1860 – 1939 · Electrical engineer · Hungary
Co-inventor of the closed-core ZBD transformer, credited with naming it.
1853 – 1942 · Electrical engineer · Hungary
Led the Ganz electrical department where the ZBD transformer was made.
1854 – 1938 · Electrical engineer · Hungary
Third member of the ZBD team; worked on parallel-connected distribution.
1858 – 1916 · Engineer and inventor · USA
Built Westinghouse's first practical transformers and the Great Barrington system.
1862 – 1919 · Electrical engineer · Russian Empire, worked in Germany
Pioneered three-phase motors, generators and transformers at AEG.
1875 – 1956 · Engineer · Germany
Invented the gas-detecting relay that protects oil-filled transformers.
1902 – 1977 · Inventor and researcher · USA
Invented cold-rolled grain-oriented (CRGO) electrical steel.
Where it happened
Sources
Dates marked “c.” are approximate, and historians sometimes disagree about who was first. If you spot a mistake, tell us.
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