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  • Writer's pictureScott Johnson

Three-The Magic Number?

Updated: Mar 14, 2022

I've long thought that three is the magic number...that everything in the universe is relative to three. How many times have we heard that trouble or bad news comes in three, or that two is company but three is a crowd? Let us consider the three-phase induction motor which is the prime mover of our modern industrial age.


Nikola Tesla is widely credited with inventing the induction motor, and receiving a patent on it in 1887. He was working for George Westinghouse, whom was developing a method of generating and distributing AC current through a grid system to power the United States. Prior to his work, DC current was utilized, but the main disadvantage to DC current is what is known as I2R loss. To flow, the current must increase twice to overcome the resistance of the conductor. This caused a problem with distribution, as the current required to overcome resistance in a distribution system would increase by two times for every unit of resistance offered by the wiring. Long runs of wiring were impractical and the high current required to overcome the impedance of the wiring led to the wiring becoming a heater! Electrical current wants to "do work", and if this "work" cannot be converted into mechanical effort, it will find a way to "do work" and results in heat. This is how the toaster that made your morning breakfast staple works, and is an example of a purely resistive load. The Nickel-Chromium wire that forms the grid inside the toaster has a low resistance, and the flow of current through that grid is high, and it gives off it's energy in the form of heat. The only way to overcome this loss in distribution and to avoid high-temperature wires or extremely large conductors would be to have a generating station at every household. Home generators, powered by kerosene-fueled engines were common in the late 1800s and resulted in a very unaffordable method of power generation.


George Westinghouse knew of this problem, and set out to overcome the problem. He developed AC or "Alternating Cycle" current in which the current flows through a conductor first in one direction, and then backwards in the other direction. In the United States, this reversal takes place 60 times per second, and is why we refer to it as "60 Hertz". It is why most electric motors operate at speeds that are multiples of three....900, 1200, 1800 and 3600 rpm. Another advantage is that AC current can be "Transformed" from one voltage to another. At the powerplant, the current generated is at a high potential, usually at 115,000 volts. This high voltage results in a lower current because of Ohm's Law, and can be distributed for long distances without suffering high I2R losses. Transformer "substations" drop this voltage, and the current is then distributed at a lower voltage, but through larger wires.


Outside of your home, there is yet another transformer that drops the voltage to 240 volts prior to entering your house. This system is a "two-phase" distribution, and consists of two wires and a "neutral" bringing 240 volts to your distribution panel. High-load appliances such as your oven and clothes dryer operate on 240 volts, and 120 volts is supplied by utilizing one half of the two-phase current with the neutral connecting the load back to the transformer on the pole outside of your home. Pay attention, as the "neutral" comes into play in a moment.


Back to the story of Tesla and the three-phase induction motor. This motor operates on the principal of inductance, and is also how a transformer works. An alternating current can induce current into a conductor that is in close proximity without being physically connected to it, because of the magnetic field produced by the alternating current. The induction motor is a study in simplicity and there is no connection between the current source and the rotating element of the motor, eliminating the need for a maintenance troublesome set of brushes and slip rings, or a commutator and brushes that are found in your common DC motor. In the induction motor, a series of coils referred to as "windings" are placed in the stationary part of the motor, known as the "stator". These coils are arranged and wired so that a rotating magnetic field is present whenever current is flowing through the stator windings. The rotating part of the motor, known as the "rotor", is made in a way that resembles a hamster's wheel or a "squirrel cage" and consists of a series of bars surrounded by insulated laminations of metal. The rotor is, in effect a single-turn transformer and as the rotating magnetic field generated by the stator windings "cuts" the bars of the rotor, a current is induced into the rotor that reacts with the rotating magnetic field produced by the stator, and causes the rotor to turn, therefore converting the electrical current to be converted into torque that can then do work. Three phases of current, each 120 degrees out of phase is utilized to provide a smooth rotating magnetic field. There is a second benefit of three phases operating at 60 hertz and being 120 degrees out of phase and that is to cancel out circulating current in the rotor, but that is a discussion for another day!

The common connection of the three-phase motor is either a "Wye" or a "Delta" configuration. In the Delta configuration, the three sets of windings are connected end-to end with each phase of the incoming current connected to two ends of winding sets. The Wye configuration has each phase connected to one end of a set of windings with all three of the winding sets connected to a common point at the other end. This Wye and Delta connection is also utilized in a transformer. There are advantages and disadvantages to both, and like circulating shaft currents this discussion is best left to another day.


Let us ponder the following image:


This is also representative of a three-phase connection. See the "Wye" and the "Delta"? If the three-phase induction motor has current connected to only Father and Son, or Son and Holy Spirit, or Holy Spirit and Father, the motor will not work. This condition is known as "Single-Phasing" and it will not produce any work. However, when all three are connected the motor will produce torque, and "do work". Same with the transformer. In this example, the center or "neutral" of the transformer is the key to operation. Without the neutral, no current will flow! As a Christian, we know that Father, Son and Holy Spirit are all one and without all three God cannot work in out life. I'm still trying to wrap my head around the concept of the Holy Trinity. It is tough to understand how three can be one, and one can be three, and I'll leave you with this: The square root of three is 1.73 and any point connected to the center results in the total voltage divided by the square root of three. 1.73 also represents the ratio of a spiral. A spiral is a geometric pattern that is infinite, and like God's love, it perpetuates into infinity. I also like to think that it represents that He is, has always been and always will be. Finally, if you were to connect any point on the periphery of the Delta or Wye to the center you will get useful work out of the motor or transformer. Therefore God IS the Father, God IS the Son and God IS the Holy Spirit......but alone they are not each other. Have a rice day, y'all!

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