Alternating Current — Tesla and Westinghouse Electrify the World

On May 1, 1888, seven patents filed between October and December 1887 were granted to Nikola Tesla: they established the induction motor and the polyphase alternating current distribution system. Bought and industrialised by George Westinghouse, they solved the problem Edison's direct current could not — carrying electricity over long distances without dissipating it as heat. This is the architecture that still underpins virtually every electrical grid.

Source: spectrum.ieee.org

In plain terms

Moving electricity around is a bit like pushing water through a pipe: the stronger the current, the hotter the line gets and the more is lost along the way. The remedy is to send a small current at a very high voltage. With Edison's direct current there was no simple way to change the voltage; alternating current, by contrast, can be transformed — one transformer steps the voltage up at the sending end, another steps it back down on arrival. Tesla added a motor that runs directly on this current, with no rubbing contact to wear out. This bulletin recounts a historical episode: it announces no new result, and the present-day figures it cites serve only to convey the scale of that legacy.

Discovery

Technical explanation

Before Tesla, Edison's direct current (DC) could not be transmitted efficiently beyond ~2 km. The reason: Joule heating losses ($P = RI^2$P=RI2) are proportional to the square of the current. At constant power ($P = UI$P=UI), lowering the current means raising the voltage — but in DC there was no simple way to change the voltage.

1. The transformer — In alternating current, the changing magnetic field enables inductive transfer between two coils. Turns ratio: $U_2/U_1 = N_2/N_1$U2​/U1​=N2​/N1​. The voltage can be stepped up to 10,000 V for transmission (low current = low losses), then stepped back down to 110 V for household use.

2. The rotating magnetic field — Tesla's fundamental innovation: two or three phase-shifted alternating currents feed coils arranged around a stator. The phase shift creates a magnetic field that rotates mechanically — with no moving part in the stator at all.

3. The induction motor — A conductive rotor (copper squirrel cage) is placed in the rotating field. The currents induced in the rotor interact with the field → the rotor turns. There is no electrical contact between stator and rotor, hence no wear (unlike the commutator of DC motors).

4. The three-phase system — Three currents shifted by 120° deliver constant power (the sum of the 3 phases is always constant). This eliminates pulsation and allows smoother, more powerful motors.

Why Tesla won the war of currents

The physics was unambiguous: transmission losses are $P_{pertes} = R \times I^2$Ppertes​=R×I2. To carry 1 MW over 100 km:

Edison knew this but had invested heavily in DC infrastructure. He staged public electrocutions of animals using AC to discredit Tesla's system and backed the development of the electric chair (1890) — whose concept came from Alfred Southwick and whose engineering came from Harold P. Brown, not from Edison himself.

Causal chain

Tesla's induction motor (1888) → Niagara Falls power plant (1895) → Electrification of cities (1900-1930) → Industry of the "second industrial revolution" → Household appliances → Computing → Internet → Digital society

Anecdote

Tesla gave up his royalties on the AC patents to save Westinghouse from bankruptcy — forgoing the equivalent of billions of dollars. He died alone in 1943 in a New York hotel room, deep in debt. His work on alternating current today powers virtually all of the 31,779 TWh consumed annually worldwide (2025).

Legacy and current data

Tesla's AC system is the foundation of every modern electrical grid. Alternating current carries ~99% of the world's electricity (HVDC accounts for only a fraction, on intercontinental lines).

Limits and controversies

This bulletin retraces a simplified historical narrative. The contributions of many actors, the intermediate failures and the priority disputes are not covered exhaustively. The modern figures ("Legacy and current data" section) come from institutional sources and may vary depending on the reference body consulted.

Sources

References verified during the August 2026 fact-checking audit: pages against which this bulletin's claims were checked.

1. May 1888: Tesla files his patents for the electric motor — IEEE Spectrum
2. Early Electrification of Buffalo (transmission Niagara → Buffalo, 1896) — Engineering and Technology History Wiki
3. Global Electricity Review 2026 — Ember