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| Subject - 2-Phase? | |
| David Hyatt | This may be a stupid question but, When do you use the term 2-phase? |
| JimmyDee | As far as I know, the proper use of it is for, a not used system that is actually a 2 phase electrical system. The power generators, instead of having 3 sets of windings that that create a set of sign waves that are 120 degrees apart, (3 phase) had 2 sets of windings that create a set of sign waves that are 90 degrees apart. I think some of the old, old paper mills used this system but it is no longer used. For the 480 volt system it had no neutral, and it was a 4 wire system. Jim BTW, the only stupid questions are the ones that are not asked. |
| Chris Clement | High-leg deltas can be considered 2-phase with respect to the neutral. We use two potential transformers, one for 120 and one for 208 (90 degrees displaced) for submetering. www.micrometer.com has info about this. |
| JimmyDee | Would the 2 phase you would produce this way not be usable for power? The one I posted about is an actual 2 phase power system. I thank you for the link and when I have more time I'll check it out. Jim |
| Chris Clement | Jim - This wouldn't normally be used for 2-phase power, you are right about that. Still, this service drop is quite flexible. 120,208,240 volts, 1, 2 and 3 phase with only 4 wires! |
| Scott Vickrey | What we call single phase would be more accurately called split single phase. It's using only one phase of the primary's possible supply. This is why you call it a single phase transformer and service. By grounding the center of the coil on the secondary side of a single phase transformer you effectively create two phases 180 degrees apart. this has often left the distribution electrician scratching his head (myself included). You can see it's relative to the side of the transformer you work on. In order to keep us all talking about the same system we simply know it as a single phase system. If the power company was to come and put two single phase transformers on the pole and send you a 240/480 4 wire system (like Jim mentioned) then we would be correct in calling this a two phase system. Regardless if I'm right or wrong I used the term 2-phase in keeping with David's original question.  |
| Chris Clement | If the power company uses 2 pots to deliver 2 of 3 phases, you will still have regular 3-phase, usually in the form of an open delta. This V-shaped configuration has the same voltage between any 2 points. It's commonly done to save a pot if the load is light. If the center tap of one of the pots is grounded, you get the hi-leg delta with 90, 120, and 180 degree relationships available. You could run one of those old mill motors but you would have to buck or boost one of the voltages for symmetry. The frequency might not be right for it, however. I think those old-phase systems were 20 or 30 hz. |
| JimmyDee | quote: In keeping with the original question,  what you have described here is not what I call 2 phase. Historically, 2 phase is not a play on words or a transformer configuration, it is an actual two phase power system that is generated as a two phases system right from the generator. The Navy used it many years ago and talk about it in a Navy Electrical Manual, which I still have, that was printed in the 1960s. It has come to mean many other things but not too many people know the original meaning because it came and went fast.Jim |