Return to Answer

Another reason that AC prevailed over Edison's DC was that the AC system scaled better, as it permitted a small number of power plants far from the city, instead of a large number of small plants about a mile apart. Edison didn't just want to sell light bulbs; he wanted to sell lighting systems to businesses. There was no power distribution network and he didn't want to have to build one before he could sell light bulbs. At first he was selling lighting systems to commercial building, maybe some large apartment buildings; each building would have its own independent generator in the basement, just as you typically have water heaters today. He was initially successful because he (unlike other developers of light bulbs) was selling and installing complete systems, generator and switchgear and wiring and all, not just bulbs.

Another reason that AC prevailed over Edison's DC was that the AC system scaled better, as it permitted a small number of power plants far from the city, instead of a large number of small plants about a mile apart. Edison didn't just want to sell light bulbs; he (or, rather, his investors) wanted to sell lighting systems to businesses. There was no power distribution network and he didn't want to have to build one before selling light bulbs. At first he was selling lighting systems to commercial buildings, maybe some large apartment buildings; each building would have its own independent generator in the basement, just as you typically have water heaters today. He was initially successful because he (unlike other developers of light bulbs) was selling and installing complete systems, generator and switchgear and wiring and all, not just bulbs.

This would have saved a lot of the clutter of overhead wires in cities, but it was clear that this would not work well for small businesses or homes (what homeowner or shopkeeper wants to worry about keeping a generator running?) and thought in terms of a central power generation plant. He designed (for Westinghouse) an entire AC distribution system involving AC induction generators, step-up transformers to boost their output as necessary for long distances, then conversion through a series of step-downs to what is called "distribution voltage", and then finally to the lines that are connected to houses and light commercial buildings. This was a far more scalable system than Edison's. And, of course, AC works for light bulbs as well as for motors.

Speaking of that... Yet another reason for preferring AC is that AC, and particularly the three-phase AC that Westinghouse's system used (everywhere except at the last drop, from pole distribution transformer to house), was and remains far better for running high-power motors. All practical motors are really AC motors at heart; "DC" motors use commutators to switch the polarity to the coils back and forth as needed, to maintain rotation - essentially they make their own AC internally. But commutators require brushes, which wear out and require maintenance; they make sparks, etc. Whereas an AC induction motor needs no commutator nor even slip rings. The AC power transmission systems starts with three-phase AC generators and maintain three-phase right up to the pole transformer. So it can easily deliver three-phase where it's needed (medium and larger commercial and industrial), but the pole transformer can tap off single-phase for homes and light commercial use.

Three-phase distribution has another advantage in not needing a dedicated "return" wire.

This would have saved a lot of the clutter of overhead wires in cities, but it was clear that this would not work well for small businesses or homes (what homeowner or shopkeeper wants to worry about keeping a generator running?). Westinghouse wanted to build a hydroelectric power generation plant at Niagara Falls - one plant to run all of New York City and beyond. Tesla designed an entire AC distribution system involving AC induction generators, step-up transformers to boost their output as necessary for long distances, then conversion through a series of step-downs to what is called "distribution voltage", and then finally to the lines that are connected to houses and light commercial buildings. This was a far more scalable system than Edison's. And, of course, AC works for light bulbs as well as for motors.

Speaking of that... Yet another reason for preferring AC is that AC, and particularly the three-phase AC that Westinghouse's system used (everywhere except at the last drop, from pole distribution transformer to house), was and remains far better for running high-power motors. All practical motors are really AC motors at heart; "DC" motors use commutators to switch the polarity to the coils back and forth as needed, to maintain rotation - essentially they make their own AC internally. But commutators require brushes, which wear out and require maintenance; they make sparks (which interfere with radio), etc. Whereas an AC induction motor needs no commutator nor even slip rings. AC power transmission systems start with three-phase AC generators and maintain three-phase right up to the pole transformer. So they can easily deliver three-phase where it's needed (medium and larger commercial and industrial), but the pole transformer can tap off single-phase for homes and light commercial use.

Three-phase AC power distribution has another advantage in not needing a dedicated "return" wire. (Just FYI, the system Tesla originally designed for Westinghouse was two-phase. They changed to three-phase after the work of Mikhail Dolivo-Dobrovolsky in 1888-1891.)

Another reason that Tesla's AC scheme prevailed over Edison's DC was that Tesla's AC system scaled better. Edison didn't just want to sell light bulbs; he wanted to sell lighting systems to businesses. There was no power distribution network and he didn't want to have to build one before he could sell light bulbs. He envisioned that each commercial building, maybe some large apartment buildings, would have its own independent generator in the basement, just as you typically have water heaters today. He was initially successful because he (unlike other developers of light bulbs) was selling and installing complete systems, generator and switchgear and wiring and all, not just bulbs.

This would have saved a lot of the clutter of overhead wires in cities, but Tesla saw that this would not work well for small businesses or homes (what homeowner or shopkeeper wants to worry about keeping a generator running?) and thought in terms of a central power generation plant. He designed (for Westinghouse) an entire AC distribution system involving three-phase AC induction generators, step-up transformers to boost their output as necessary for long distances, then conversion through a series of step-downs to what is called "distribution voltage", and then finally to the lines that are connected to houses and light commercial buildings. This was a far more scalable system than Edison's. And, of course, AC works for light bulbs as well as for motors.

Speaking of that... Yet another reason for preferring AC is that AC, and particularly the three-phase AC that Tesla's system uses (everywhere except at the last drop, from pole distribution transformer to house), was and remains far better for running high-power motors. All practical motors are really AC motors at heart; "DC" motors use commutators to switch the polarity to the coils back and forth as needed, to maintain rotation - essentially they make their own AC internally. But commutators require brushes, which wear out and require maintenance; they make sparks, etc. Whereas an AC induction motor needs no commutator nor even slip rings. Tesla designed his power transmission system to start with three-phase AC generators and maintain three-phase right up to the pole transformer. So it can easily deliver three-phase where it's needed (medium and larger commercial and industrial), but the pole transformer can tap off single-phase for homes and light commercial use.

Another reason that AC prevailed over Edison's DC was that the AC system scaled better, as it permitted a small number of power plants far from the city, instead of a large number of small plants about a mile apart. Edison didn't just want to sell light bulbs; he wanted to sell lighting systems to businesses. There was no power distribution network and he didn't want to have to build one before he could sell light bulbs. At first he was selling lighting systems to commercial building, maybe some large apartment buildings; each building would have its own independent generator in the basement, just as you typically have water heaters today. He was initially successful because he (unlike other developers of light bulbs) was selling and installing complete systems, generator and switchgear and wiring and all, not just bulbs.

This would have saved a lot of the clutter of overhead wires in cities, but it was clear that this would not work well for small businesses or homes (what homeowner or shopkeeper wants to worry about keeping a generator running?) and thought in terms of a central power generation plant. He designed (for Westinghouse) an entire AC distribution system involving AC induction generators, step-up transformers to boost their output as necessary for long distances, then conversion through a series of step-downs to what is called "distribution voltage", and then finally to the lines that are connected to houses and light commercial buildings. This was a far more scalable system than Edison's. And, of course, AC works for light bulbs as well as for motors.

Speaking of that... Yet another reason for preferring AC is that AC, and particularly the three-phase AC that Westinghouse's system used (everywhere except at the last drop, from pole distribution transformer to house), was and remains far better for running high-power motors. All practical motors are really AC motors at heart; "DC" motors use commutators to switch the polarity to the coils back and forth as needed, to maintain rotation - essentially they make their own AC internally. But commutators require brushes, which wear out and require maintenance; they make sparks, etc. Whereas an AC induction motor needs no commutator nor even slip rings. The AC power transmission systems starts with three-phase AC generators and maintain three-phase right up to the pole transformer. So it can easily deliver three-phase where it's needed (medium and larger commercial and industrial), but the pole transformer can tap off single-phase for homes and light commercial use.