Harold Hallikainen harold@hallikainen.com Hallikainen & Friends, Inc. See the FCC Rules at http://hallikainen.com/FccRules and comments filed in LPFM proceeding at http://hallikainen.com/lpfm On Tue, 21 Jul 1998 11:15:05 +0200 Leo van Loon writes: >Dear friends, > >In another mailinglist a member told about a two-phase 120V net with >180 >degrees phase difference in parts of the US. I do not understand how >high >power induction motors can be used with such an electricity supply. >Three >phase rotary currant was invented for this type of motors. >Can anybody from the States tell me about the finesses of this type of >electricity supply? > This is generally only used in residential electric supplies. A single phase of the three phase power on the pole is run thru a transformer with a 240VAC center tapped secondary. We then have two hots and a grounded neutral. 240VAC single phase loads (like heating loads) are run between the two hots. Single phase loads are run hot to neutral. In industrial environments, we either have three phase delta or wye. The wye is used where there are a lot of 120VAC single phase loads, since they can be connected between any hot and neutral. You get 208VAC between any two hots, which is acceptable for many 240VAC single phase loads (though not all). Other places have a three phase delta connection where each transformer secondary is 240VAC. One of the secondaries has the center tap grounded and is used as a neutral. Single phase 120VAC and 240VAC loads use this secondary. The third lead (the wild phase) is 208 volts above ground. Sometimes we get an "open delta" with only two transformers. These are not favored much. Now, questions on European (and elsewhere) power. I've read about limitations on harmonic line current. Though I have not read the standards (IEC standars are expensive!), it appears these standards apply to equipment that draws more than 16 amps. We manufacture phase controlled light dimmers, which draw more than 16 amps. Is the 16 amp limitation (if I've read correctly) a recognition that below this current it is practical to use some sort of power factor correction and above it phase control is indeed the most efficient way to control large loads? I'd be interested in hearing more on this (regulation of power line harmonic current) anywhere in the world! Thanks! Harold _____________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com Or call Juno at (800) 654-JUNO [654-5866]