At 10:49 PM 4/22/2007 -0400, you wrote: >CT - > >Why voltage choices?
The phase-phase voltage amongst the IOUs (commercial) utilities is 12 kV in CA. The most widely used voltage in North America is 12.47 kV, which is 7.200 x 1.73. So your pole transformer is 7,200Y Gnd/240. 7,200 is 3 X 2,400 V. 2400=20 X 120. 120=one of the old Edisonian lamp voltages. 2400 4160 7200 12470 "12.5 kV" 24940 "25 kV" But here's the progression of most common sub- transmission & transmission voltages in NA: 34.5 kV 46 69 115 138 161 230 345 500 (East Coast Grid voltage) 765 (American Power System, only) Except for the last two, they are based on the old Edisonian lamp voltage of 115 V. 12 kV in CA is 6.9 kV x 1.73 (really 11.937 kV). But there are "legacy" voltages that are no longer built upon new: 6.6 kV 44 (Duke Energy subtransmission [and now distribution]) 33 (old Carolina Power & Light Co.) 66 (Southern California Edison) 110 (now replaced by 115) 132 (Southern California Edison) 220 (now replaced by 230) These are based on the old Edisonian lamp voltage of 110 V. Edison's lamp company built lamps and segregated them into three voltage classes according to their nearest most efficient terminal voltages: 110, 115 and 120 V. Then he assigned generator voltages to his companies to accommodate these voltages. Therefrom came the above voltages. A very little known fact. 95% of electricians & engineers don't know that. Subtransmission is that part of the bulk power system whose purpose is to energize distribution substations. But with the push for higher voltages for greater efficiency, many old transmission voltages became sub- transmission voltages, and lower subtransmission voltages became distribution. 34.5 kV is a common distribution voltage out here. Old 34.5-kV delta subtransmission systems were re- configured to Y, neutrals run, and became distribution. The highest distribution voltage I've seen personally is 46 kV, belonging to Alleghany Power Co. Also still used to energize distribution substations. Duke's counterpart is 44 kV, used in same circumstances. Transmission systems look to be delta, but are in fact grounded Y systems. The neutral isn't there in function (doesn't need to be) but in fact, as the overhead ground conductors (lightning protection) run continuous from transmission substation to substation. You look at a transmission transformer, you see three conductors in and out, but the neutral is there...only it's connected to the tank and ground. And the big step-down and step-up transformers are almost all autotransformers. A 230/115-kV stepdown is centertapped. Okinawa Power Corp. used 13.2, 66, 132, and 264 kV But Japan and Korea now use 120-V based systems. Japan uses 1,000 kV for a grid voltage! Europe, Middle East and Africa use 11, 22 and 33 distribution voltages. Delta. Now you know just exactly what your little heart wanted to know. Sparky Charles A Taylor, WD4INP Greenville, North Carolina _______________________________________________ IRCA mailing list [email protected] http://montreal.kotalampi.com/mailman/listinfo/irca Opinions expressed in messages on this mailing list are those of the original contributors and do not necessarily reflect the opinion of the IRCA, its editors, publishing staff, or officers For more information: http://www.ircaonline.org To Post a message: [email protected]
