Considering a Squirrel Cage 3 phases motor. A multi-switch receive the 3 lines of the 3Ø power L1 L2 L3 and distribute the voltage to 6 wires. The multi-switch has 3 position, Speed 1 , OFF , Speed 2, or Low , OFF , Fast.
Schematically, there are 6 coils but each coil is built with 3 winding, hence a total of 18 physical winding . Each coil is calculated to be identical DC resistance of 30 ohms. Each coil are connected in series like in an hexagon (schematically speaking). The 6 coils are electrically accessible via 6 wires. After careful testing and analysis it is established that the multi-switch when positioned for Speed 2, will short 3 of the 6 wires such that the connection configuration becomes Star (see images below), if the switch is set to Speed 1 the configuration is Delta. Switch position OFF disconnect all wires from power.
In the case of Speed 1 (Slow), there are 3 coils (let’s call them Ua , Va , Wa) that are shorted together, which imply that when in Star configuration, the magnetic polarity of those 3 coils is reverse compare to the Delta configuration, while that 3 other coils ( Uv , Vb , Wb) remain with the same magnetic polarity.
Below is an image to represent the physical distribution of 6 of the 18 winding involved. It is clear that each coil will produce a magnetic field and that the sum of all 18 magnetic field will result in one magnetic field that will turn 360 degrees per cycle. That is the basic principle of an induction motor.
I have much difficulty wrapping my mind around the fact that reversing the polarity of 3 coils (9 winding) would not interact with the 3 other coils (again 9 winding) and produce a counter induction that would create heat just as it would happen if one was to connect in parallel the output of two transformer with wrong polarity and or phase. At one point some of the induced magnetic of each coil would induce a voltage in the next adjacent coil, creating some sort of counter-current, producing a loss of energy into heat.
Furthermore, how is it that by distributing the same voltage into 6 series connected coils would induce double the speed of the other case where now the 6 coils are turned into 3 coils ( 3 times two coils in parallel) . Such configuration would “pull” more current, intuitively resulting into an increase speed, instead the speed is lowered.
The Questions: 1- How are multiple winding energized with voltage of different phases and polarity not induce heat ? Basically I am trying to understand what exactly is magnetically happening in this Speed 1 configuration.
2- Why is it that when connecting in parallel two winding would result in a lower speed instead of a higher speed ? ( I guess if I would understand what’s happening from question 1, then question 2 would be answered).
Any WEB source of theoretical explanation is more than welcome. Cheers