Nikola Tesla and His Perfect Electric Motor
In the early days of electric power development in the US, it appeared that a direct current system, backed by Thomas Edison, might win out. One reason was that there were direct current motors, but none for alternating current.
That changed in 1887 when Nicola Tesla invented the motor described here, a type that is still in widespread use. As the first graphic shows, Tesla’s design had three electromagnets spaced 120 degrees apart in the outer, fixed, part of the motor. Each electromagnet is driven by AC current, so that the magnetic field that it produces changes back and forth, varying as a sine wave. At any moment in time, the magnetic field in the center is the (vector) sum of the fields produced by the three electromagnets.
The rotor (not shown) is in the center, where the magnetic fields intersect.
The animation shows how the three vectors add together to produce a net magnetic field (black) that rotates at a constant rate. This rotating field pulls the rotor around, producing power.
It’s a brilliant conception – the rotating field is produced without using moving parts or switches. Also, the strength of the field (i.e., the length of the black vector) is constant, so that the motor’s torque does not vary as the rotor turns, which results in constant, vibration-free, power output.
To show that the three vectors add up in this way, some trigonometry equations are required. A student told me once that trig identities had no practical use, and I said that Tesla’s motor, and our electric power system, might not exist without them.
[added: it’s called a three phase motor, because the input currents fed to each electromagnet are not “in-phase” – their sine wave peaks at different times, 120 degrees apart.]
#physics
No comments:
Post a Comment