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| Subject - definition of 3-phase | |
| Mitchm221310 | I am currently a stationary engineering student. I need a definition of 3-phase, single-phase and 2-phase. can someone please help? |
| JimmyDee | Looking at a graph, the three phase power will be represented by 3 sign waves of the same magnitude, 120 degrees apart. This is produced by 3 separate coils in the generator that also are 120 degrees apart. Single phase is represented by 1 sign wave on the graph and is produced by a single set of coils. 2 Phase is represented by 2 sign waves that are 90 degrees apart. This is produced by 2 sets of coils placed in the generator, 90 degrees apart. Jim |
| Scott Vickrey | Mitch please inform us (or at least me) what is a stationary engineer? |
| JimmyDee | I hope it is not one that doesn't move.  Jim |
| wareagle | I didn't know what a Stationary engineer was but Google provided this site http://www.iuoe.org/stationary/stationaryfield.htm. |
| kingofmars | I could be wrong, please correct me if so, but to Jimmydee wouldn't the sine waves of a two phase system be 180 degrees apart, king |
| cs409 | single phase, is a 180degs ,,,2 phase is 90 degs....3 phase is 120.... |
| JimmyDee | quote: No and I am reading directly from the Navy manual (about 1960 vintage)in front of me. "In a 2-phase a-c generator there are two single-phase windings physically spaced around the stator so that the a-c voltage induced in one is 90 degrees out of phase with the voltage induced in the other. In a 2-phase system the windings are electrically separated from each other." If you think about it the two windings are placed, first one on the 0-180 degree axis and the second one on the 90-270 axis. Jim |
| cs409 | jimmy, while your looking in that book,,, does it have any xfmers diagrams shown? seems like the only 2 phase sys i have ever seen was an old ww2 manufacter plant in waco tx!! and the service feed from untility was a mess from hell...it wasnt in service just the remains... |
| JimmyDee | No it doesn't. But I'll try to remember and explain the system best as I can. The 2 phases are electrically separate, so you would have 2 transformers. This system is a 4 lead system. (A, B, - C,& D) A & B would feed one single phase transformer and C & D would feed the other. There is no electrical connection between A,B and C,D at all so it is fairly straight forward. (I think) It looks like phase identification would be very important because you couldn't mix either single conductor from one group with the other group.  From ElectricalKnowledge's Free Images and Drawing Collection If you look at the sine waves (which are in the book)it shows at 0 degrees one sine wave starting, 90 degrees later the next and then 180 degrees before the first one starts again. It not a nice symmetrical flow like the 3 phase. I should imagine that the starting torque would be close to a capacitor start motor because that is what the starting winding is out of phase with the running winding on a cap start motor. (90 degrees) Jim |
| Scott Vickrey | Here's a diagram of a 2 phase generator. I made it just for you.  From ElectricalKnowledge's Free Images and Drawing Collection |
| Seawolf | Jeez, this brings back memories. 2-phase generators (Amplidynes) were used in the Navy as the reference signal for voltage regulation on SSTG's (turbine generators) and they spun at 10000 RPM (on the generators I worked on). This output was converted by a Scott-T transformer to shift the phases by 90 degrees so the voltage regulating unit could use the signal. Another more common application of 2-phase generation are rotary pulse encoders - 2 phases 90 degrees out of phase used as a speed reference signal to a variable speed Dc drive. |