Electric utilities genreate and distribute 3 phase power. At the load, then, some power conversion strategy is employed to derive 2 phase power. For instance, by adding a secondary winging on a 3 phase transformer on phases A and B with 47% of the winding on phase A and 53% on phase B, the resultant is a voltage lagging phase A by 90 degrees. The turns ratio between primary and secondary is adjusted to get the desired secondary voltage on the "new" phase.
This is essentially what capacitor start single phase motors do -- temporarily derive a phase approximately 90 degreees from the single phase, so that there is some rotational torque for starting. Once running, this is no longer necessary and the start winding drops out. On a 2 phase motor, the second phase remains in the circuit. John P. Wagner Regulatory Compliance & Mandatory Standards AVAYA Strategic Standards. 1300 W. 120th Ave, Room B3-D16 Phone/Fax: (303) 538-4241 [email protected] > ---------- > From: Hans Mellberg[SMTP:[email protected]] > Reply To: Hans Mellberg > Sent: Saturday, December 15, 2001 11:00 AM > To: Cortland Richmond; [email protected] > Cc: Robert Johnson; 'Barry Esmore'; 'EMC-PSTC Forum' > Subject: Re: 2 Phases in North America > > > ok folks. This topic needs to be clarified. > > With respect to each other, by definition, two conductors have a > potential > difference at 180 degrees. Period. The 90 degree stuff may pertain to > current but > not to voltage. You would need a four-phase transformer to get 90 > degree phasing and > simply it does not exist. Voltage, is usually measured: wrt ground, > wrt other > reference conductor such as neutral or wrt to another voltage (hot) > conductor. In > some cases, the voltage difference between ground and two other > conductors may be > 120/240 degrees such as in a three phase system. So, no matter how you > measure > voltage it will either be at 120, 180 or 240 degrees wrt to some other > conductor. > > In the US there have been many systems of low voltage (staying below > 480V)distribution yielding the following voltages: > > 480/240/120 > 480/208/120 from three three phase > 480/230/115 single split phase > 230/115 single split phase motor control voltage > 220/110 single split phase older home voltages > 208/120 from three phase > 480/277 (for fluorescent lighting) > 117 (where did this come from? seen in many older HP instruments) > Open Delta (3, 4 or 5 wire, when one is grounded into neutral its > called a > "stinger") > Split phase (three or four wire) > Y (four and five wire) > > Hope this stirrs the pot!!!! > > > ===== > Best Regards > Hans Mellberg > Regulatory Compliance & EMC Design Services Consultant > By the Pacific Coast next to Silicon Valley, > Santa Cruz, CA, USA > 408-507-9694 > > __________________________________________________ > Do You Yahoo!? > Check out Yahoo! Shopping and Yahoo! Auctions for all of > your unique holiday gifts! Buy at http://shopping.yahoo.com > or bid at http://auctions.yahoo.com > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Michael Garretson: [email protected] > Dave Heald [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > Jim Bacher: [email protected] > > All emc-pstc postings are archived and searchable on the web at: > No longer online until our new server is brought online and the > old messages are imported into the new server. >
