It's perfect for running two phase motors, which were, I understand, an eariler invention than three phase motors. If you've got antique plant two phase might be useful.
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Huh? That's what the scott transformer does.
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What is the difference between a two phase (90 degree) motor and a single phase motor with a starter winding, in which the starter winding is powered by a capacitor from the single phase ? Is the starter winding weaker ?
On a two phase motor with equal windings 90 degrees apart and with a capacitor between the two winding hot ends and connecting the single phase to either end of the capacitor will run the motor. Depending of which capacitor end is connected to the phase, the motor runs either CW or CCW.
Is there a reason, why an inductance is used instead of capacitance to achieve the 90 degree phase shift ?
Okay, it just stuck me that he is using his self-generated 2-phase power when possible, but then uses commercial 3-phase with a Scott-T to provide standby 2-phase power. I was thinking that he was applying three phase power to a 2-phase motor when not generating his own power. My mistake.
some people get easily confused.
Two phase motors were good because you can run the motor the direction you need without using a starter phase or capactor and on top of that get the standard utility voltages for other items, two legs worth plus common. The 2 phase AC motor with slip ring motor to bring the rotor out for shorting via a rheostat was a good form a soft starting and speed regulation back then. Later you could get 3 phase motors working the same way, then they came out with Eddy current clutches, AC tachs as feed back. TUBE amps for the eddy current coils with the AC tach as the feed back to generate the pinch off voltage on the grid ;)
I feel old.
Jamie
Maybe they were way back then. But you can dispense with the Scott-T and use a 3-phase motor to run in the direction you need. And you don't need a capactor (sic). Still 3 wires for a delta connection.
The same can be done with a 3 phase motor.
Do know anything about electricity? From any two (non-co linear) phases, one can construct any other phase relationship. That's the function of the Scott-T.
It is equally simple to switch the motor from CW to CCW by interchanging two phases in a three phase system.
It is also easy to make soft starter in a 3 phase system by starting in wye and run in delta.
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It is hard to believe that they had built o much two phase infrastructure that they would continue building it, after the superior three phase system was invented.
40+ years ago I worked in a Philadelphia factory building which had a bit of two-phase wiring still in place which had last been used in the 1940's IIRC, and was considered obsolete long before then, with three-phase powering most equipment. The building was reputed to have originally been the first indoor movie studio back when full sunlight was required, accounting for the greenhouse-like construction of 3 walls and the roof, which should give some indication of when the original two-phase power was installed.
Higher torque ripple, lower efficiency, needs 4 wires instead of 3, it is a wonder any of it lasted until the 1940's.
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