jim dungar said:
Based on your written description, reference books I have seen call this a 2-Phase 5-Wire system.
I have never heard of 4-phase star, I would be interested to hear more about it.
I work with 'high phase order' electric motors. Once you start talking about anything other than 3 phases, the naming conventions are not really well settled.
A star connected motor is one in which all of the 'phase circuits' are connected between a supply terminal and a common point. The 3 phase star is commonly called 'wye', where the phase circuits connect between your three supply terminals and the common.
A mesh connected system is one in which all of the 'phases circuits' are connected between two supply terminals, and a common point is not used. The 3 phase mesh connection is commonly called 'delta'.
The system that rattus described is a 'star' because you have that common point in the center.
At least one of the authors in the field would call the system that rattus described a '4 hemi phase system'. The reason is that 'phases' 180 degrees apart do not better define rotating field production, as discussed when we were talking about center tapped transformers and 180 degree phase difference versus inversion. This author would require phase angles of 0,45,90,135 (or others better balanced) to call the system a '4 phase system'.
In the systems that I work with, we regularly have physically separate inverter outputs, each with its own electronically synthesized and electronically adjustable phase angle, set up to operate with a 180 degree phase difference. For example, the machine that I am testing now has 18 separate inverter output terminals, at 0,20,...180,200,220,...320,340 degree relative phase. I call that an 18 phase machine, and thus I would call the system that rattus described a 4 phase system.
A motor supplied using 2 phase 5 wire has exactly the same number of 'pole-phase groups' as a motor supplied using 2 phase 3 wire. There is a benefit: for the same 'phase' voltage relative to the grounded conductor, the 5 wire system is more balanced, and thus can deliver the same amount of power with less current flow on the grounded conductor.
A system that we've discussed for powering computers is a transformer bank that has a delta connected primary, but where all three secondary coils are _center tapped_ single phase secondaries, where the center taps are grounded and the secondary 'end terminals' are separate ungrounded terminals. This system provides _six_ separate ungrounded terminals, with phase angles 0,60,120,180,240,300. Some would call this a six phase system, some would call it a three phase system, one a 6 hemi-phase system, and most of us 3 separate single phase systems. The idea was to design a system that uses common components without 'super neutrals' to deal with triplen harmonic issues.
-Jon
