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.
Original patent title: “Electrical Transmission Of Power”
What this patent covers
The actual claim
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 this patent does NOT cover
The boundaries
- 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)
These exclusions are unique to PatentBrief — derived from the actual claim language, not patent-office boilerplate.
What made this novel
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.'
Schematic visualization of the patent's claim structure. Hand-drawn diagrams in progress for each landmark patent.
Where you've seen this
Real-world examples
Every household appliance with a motor — washing machines, refrigerators, fans, air conditioners — uses a version of this principle
Industrial factory motors that run 24/7 for decades without brush replacement
Tesla Motors named itself after this patent and this inventor
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
Why it matters
The bigger picture
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.
Granted
May 1, 1888
Claim 1 — Plain English
What this patent 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.
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.'
What it does not 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)
PatentBrief Score
Impact Score
Limited data
Citation count
6/40
Early citations
Claim breadth
0/20
Narrow claims
Recency
0/20
Older than 20 years
Assignee scale
0/20
Independent or smaller assignee
PatentBrief Impact Score — based on citation count, claim breadth, recency, and assignee scale. Not a legal assessment.
Glossary
Key terms defined
- Induction
- The process by which a changing magnetic field induces an electrical current in a nearby conductor, without physical contact
- Polyphase
- Using two or more AC currents that are offset from each other in time — this offset is what creates the rotating magnetic field
- Commutator
- The mechanical device in DC motors that periodically reverses the current direction to keep the motor spinning — the thing Tesla eliminated
- Rotating magnetic field
- Tesla's key insight: combine two out-of-phase AC currents in two sets of coils and the net magnetic field rotates continuously around the motor's core
- Alternating current (AC)
- Electrical current that reverses direction many times per second (60 times per second in the US, 50 in Europe) — as opposed to DC, which flows in one direction
Citations
Patent lineage
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