I was taught that if you want to change the direction of a three phase rotating machine that is rotating in forward direction, you interchange the phases. Since the phases has the same features (voltage and current), what is responsible for making the machine to rotate in reverse direction, when the phases are interchanged?
How to change rotation direction of 3-phase electrical machines
motorthree phase
Related Solutions
If you have access to internal connections between the coils, you can reverse the motor by reversing the connection of one coil with respect to the other one.
The easiest way to think of three phase is as three "hot" wires and one neutral wire. Between any hot wire and neutral you will measure (say) 230 volts AC and usually a single household will receive one hot wire and neutral. Several houses further down the street a house might receive one of the other hot wires and neutral.
There are three circuits sharing a common wire called neutral and, as far as any single phase household is concerned they "see" a hot (live) and a neutral. Different names in different countries sometimes of course.
You could mistakingly supply two hot wires to a house and the voltage wouldn't be 230 V AC anymore - it would be about 400 volts because "line-to-line" voltage is \$\sqrt3\$ times bigger than line to neutral (often called "phase voltage"): -
So if Va is 230 volts and Vb is 230 volts, Vab is about 400 volts. It's just geometry.
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Best Answer
The windings in a 3 phase motor, when activated by a 3 phase supply produce a rotating magnetic field in the rotor area of the motor. Swapping phase A with phase B re-orders the fluxes so that the flux rotates in the opposite direction. Swapping B with C does exactly the same thing as does swapping A with C. Think of it like a triangle with corners called A, B and C. If you swap any two corners and follow the points A, B and C you'll go in anopposite direction. Swap two more corners and you're back to the original rotation.
This is what it looks like. The black arrow is the flux produced by the three phase windings: -
Clearly, if yellow phase were swapped with blue phase the rotation would be opposite.