76nemo
Senior Member
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- Ogdensburg, NY
76nemo said:According to the poll so far, it seems to be averaging
So much for RMS
:grin:
single-phase?
- Thread starter hardworkingstiff
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So much for RMS
:grin:gar
Senior Member
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- Ann Arbor, Michigan
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- EE
080411-1837 ESR USA
Consider crossman's very nice diagram. I agree there are three phases available.
The sum of sine waves of the same frequency but different phase angles is still a sine wave.
For illustration purposes. Connect one transformer primary across A to N and a second one from B to N. Connect the two secondaries in series, appropriately phased, and with the correct turns ratio and you can synthesize the third balanced leg C. I believe you will find the turns ratio for each transformer is 1/2. Draw the vector diagram. Note sin 30 or cos 60 is 1/2. The vector component 60 deg from one leg of a 120 V leg to nuetral is 60 V, and 60 + 60 is 120.
.
Consider crossman's very nice diagram. I agree there are three phases available.
The sum of sine waves of the same frequency but different phase angles is still a sine wave.
For illustration purposes. Connect one transformer primary across A to N and a second one from B to N. Connect the two secondaries in series, appropriately phased, and with the correct turns ratio and you can synthesize the third balanced leg C. I believe you will find the turns ratio for each transformer is 1/2. Draw the vector diagram. Note sin 30 or cos 60 is 1/2. The vector component 60 deg from one leg of a 120 V leg to nuetral is 60 V, and 60 + 60 is 120.
.
gar
Senior Member
- Location
- Ann Arbor, Michigan
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- EE
080411-2058 EST USA
If you have at least two magnetic vectors at a suitable angle in physical space and excite these with ac signals of the same frequency that are not in phase, then you get some form of a rotating magnetic field in space. Multiples of 180 degs are not considered out of phase. With a rotating magnetic field you have the basis for a self starting ac motor.
All single phase motors actually have some way of generating the phase shifted magnetic vector, and at least for starting are a form of 2 phase motor.
Also note the correct ratio from a phase to phase 208 for a balanced 3 phase Y is 208/sq-root3 = 208/1.732 = 120.1 and not 117. 117 would relate to 202.6 . As a very rough statement 208/117 is ok, but I like 208/120 better.
.
If you have at least two magnetic vectors at a suitable angle in physical space and excite these with ac signals of the same frequency that are not in phase, then you get some form of a rotating magnetic field in space. Multiples of 180 degs are not considered out of phase. With a rotating magnetic field you have the basis for a self starting ac motor.
All single phase motors actually have some way of generating the phase shifted magnetic vector, and at least for starting are a form of 2 phase motor.
Also note the correct ratio from a phase to phase 208 for a balanced 3 phase Y is 208/sq-root3 = 208/1.732 = 120.1 and not 117. 117 would relate to 202.6 . As a very rough statement 208/117 is ok, but I like 208/120 better.
.
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