Posted 18 July 2002 - 07:59 PM
Posted 18 July 2002 - 11:28 PM
I'll have a go at a simple explanation:D
Consequent poles are the key to simple two speed motor design. Consider the basic operation of a two speed motor, to keep things really simple lets only focus on the windings connected between two phases only. This particular imaginary motor has only two physical poles, with each pole having one winding only with two wires. Therefore to complete our simple picture we have two physical poles, 2 windings and four wires.
If we connect these windings in SERIES and apply AC, at each half of the AC waveform we end up with one North pole and one South pole alternatively, as most would expect, giving us a 2 pole 3000RPM nSnc motor. So far so good?
NOW, if we connect these same windings in parallel and connect to the same AC supply, at each half of the mains waveform we end up with TWO North poles and TWO South poles alternatively. At first glace, this may seem to provide no useful result with no magnetic field / rotor interaction. The reality is quite different though. What actually happens is that when each pole becomes, say, North, the stator iron in the two areas between the two poles becomes South. A consequent pole is produced! We now effectively have a 4 pole 1500RPM nSync motor, simply by changing our winding connections from series to parallel, the parallel connection producing consequent poles. Cool or what?
If the above doesn't make sense, try drawing a sketch of a simple motor with two poles, two windings and four wires, such sketches work for me.
Hope this is helpfull.
Posted 03 January 2003 - 07:13 AM
Consequential poles is not about series or parallel connections. It is about the direction of current flow in the pole bands. In a 2 pole motor, if the current in both the pole bands flows in the opposite directions, we get two opposite poles (N & S) and hence a speed of 3600 RPM (60 Hz) and 3000 RPM (50 Hz). If the current in both the pole bands flow in the same direction, then you get two like poles (NN or SS). Since magnetic field is not open ended, two poles of opposite polarity (SS or NN) are automatically created leaving us with 4 poles with a resultant speed of 1800 RPM (60 Hz) and 1500 RPM (50 Hz). These results can be achieved with both series and parallel connections.
The series or parallel connection is about handling currents carried by the winding wires. If the current is small, the winding wire area is small and a series connection will suffice. If the current is large, then winding big size wires poses practical problems and hence parallel connection is used to split the current and the smaller size wires are used accordingly.
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