Rick, and group members, I thought that I would weigh in with an opinion on this one. The definition of phase should be determined by the requirements of the equipment. If the equipment only requires single phase power, regardless of voltage, then that is what should be specified. It does not matter if this single phase is derived from a three phase source, it is still single phase.
One way to determine this is to ask yourself if the equipment could be powered from a single phase electronic ac source. In my experience true two phase equipment is extremely rare. Instead, what we usually find are racks of equipment intended to be supplied from split phase (such as the typical U.S. residential service). This is because the rack either contains a mix of 120V and 240V equipment, or the 120V equipment draws too much current for a single circuit and must be split into two groups. None of these setups actually require two phases of the same source and could easily be rewired to operate from completely separate circuits. If anyone is still confused, here is some (greatly simplified) background on electrical power generation. Single phase alternators (often mistakenly called generators) produce a single sinusoidal cycle for each revolution of the input shaft. Frequency is determined by rotational speed. If an additional connection is made at the midpoint of the winding the alternator becomes a split phase type such as the 120V/240V types commonly sold as portable power sources. Three phase alternators have additional windings that each produce a single sinusoidal cycle for every revolution of the input shaft. These waveforms are staggered in time so that the peaks do not coincide with each other. This is the most efficient way to generate electrical power. This is why power companies use them. Automobile alternators are also three phase. The outputs are rectified by diode pairs to produce a pulsating dc output. The battery acts as a filter. If an oscilloscope lead is placed right at the alternator terminals a slight trace of the waveform can be seen. It is possible to detect "blown" diodes that way. Scott Lacey -----Original Message----- From: owner-emc-p...@ieee.org [mailto:owner-emc-p...@ieee.org]On Behalf Of rbus...@es.com Sent: Wednesday, May 02, 2001 4:31 PM To: emc-p...@majordomo.ieee.org Subject: AC Power Primer? I am in the process of assisting our publications group with documenting an ac power configuration. As simple as this sounds, it turns out there are varying opinions in our engineering group regarding the naming convention for input power, in particular single phase verses two phase. We all probably agree that a phase to neutral connection is single phase and devices that use all thee phases, whether they are 208V 60Hz or 400V 50Hz, are truly three phase. The discussion heats up when you are talking about a phase to phase connection on a three phase distribution (208 or 400V). Is this called single phase or two phase? It has been suggested that in the European community it is called two phase, while in the U.S. we call it single phase. I am looking for opinions or discussion on this issue. On a related note in the U.S. we have 240V 60Hz (two 120V drops) coming into our into our homes. This is provided by a transformer with a center taped winding. On the outside legs of the transformer we have 240V but between either outside leg and neutral (center tap) we have 120V. I would call this a single phase system with two additive (in phase) 120V windings. Again others have called this two phase. My apologies to the group if this is a stupid question. Its just one of those nagging questions. Rick Busche Evans & Sutherland Salt Lake City, Utah rbus...@es.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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: pstc_ad...@garretson.org Dave Heald davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on "Virtual Conference Hall," ------------------------------------------- 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: pstc_ad...@garretson.org Dave Heald davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on "Virtual Conference Hall,"
