Tesla's AC Induction Motor: How Alternating Current Powers the World

Nikola Tesla's 1888 patent describes an electric motor that runs on alternating current (AC), eliminating the need for brushes or commutators and making long-distance electrical power transmission practical for the first time.

What it covers

This patent covers a motor that rotates purely from the interaction between magnetic fields — no mechanical contact, no brushes, no sparks. Tesla's insight was that by feeding two alternating currents slightly out of phase with each other into separate sets of coils, you could create a rotating magnetic field. That rotating field then pulls the rotor along with it through electromagnetic induction, which is why it's called an induction motor. The result was a motor that was fundamentally simpler, more reliable, and far cheaper to build and maintain than any DC motor of the era. Combined with AC generators and transformers, it made it economically viable to transmit electrical power over long distances — something Edison's DC system could never do.

What it doesn't cover

• —DC motors of any kind
• —Synchronous motors where the rotor spins at exactly the same speed as the magnetic field
• —Electric generators (though the same principle applies in reverse)
• —Any specific use case for the motor — the patent covers the abstract principle, not the application
• —Single-phase AC motors (this patent requires polyphase / multi-phase AC current)

The clever bit

The genius isn't in the motor itself — it's in the realization that you don't need to mechanically commutate anything. By using two or more AC currents that are out of phase with each other, the magnetic field inside the motor rotates automatically. The rotor just chases that rotating field. No brushes means no wear, no sparks, and no maintenance. Tesla filed this while working for Westinghouse, and it became the weapon Westinghouse used to defeat Edison in the 'War of Currents.'

Why it matters

This patent, along with Tesla's AC generator patents, is why you have electricity in your home. The War of Currents — Edison pushing DC, Westinghouse/Tesla pushing AC — was settled in AC's favor largely because the induction motor made it the superior system end-to-end. Edison's DC system required power stations every mile. Tesla's AC system could transmit power hundreds of miles. The Niagara Falls generating station (1895) was built on Tesla's AC system and proved the concept at scale. Every power grid on Earth still runs on alternating current. The motor in your dishwasher is a direct descendant of this patent.

Real-world examples

• 1.Every household appliance with a motor — washing machines, refrigerators, fans, air conditioners — uses a version of this principle
• 2.Industrial factory motors that run 24/7 for decades without brush replacement
• 3.Tesla Motors named itself after this patent and this inventor
• 4.The entire AC power grid — the reason you have 60Hz (or 50Hz) power coming from your wall — was built around making motors like this work

Glossary