View Full Version : two phase, dc or other? weirdest system youve worked on?
05-30-2006, 07:45 PM
being in miami, finding old stuff is an extreme rarity. last storm season we found 3 transformers, reportedly in a crazy wye bank from 1923. theyre ge, 2 75's and a 100... im "shocked" we had 7620 back in those old days.
so it brings to mind, whats the weirdest system (utility supplied) you guys have ever worked on? 2 phase? dc distribution or transmission? any really odd ball voltages of standard connections?
05-31-2006, 10:21 AM
In Philadelphia, PA we worked on two phase primary systems that still existed in small pockets of the city. There were two primary phase wires and an additional wire that was referred to as the "B" wire. It was the return. The voltages were 2400 to ground on any phase wire and 3400 a-c (2400 times 1.41, square root of 2). Getting normal residential services off this primary system was not an issue, obviously. Getting three phase was a little more complicated. Using two single phase pots, each pot coming off one primary phase, one pot would feed the lighting load and the other pot would feed another pot that we called an "auto". That was a single winding pot that had 4 bushings on the front and was wired in such a way as to produce two 120 volt legs and one high (208) leg. The second pot fed the auto 240 volts and the 208 leg went with pot 1's two 120 volt legs to give the cust 120/240 4 wire delta. No wye secondaries were available.
There were also 5 wire, two phase secondaries. 2 wires were "a" phase and two wires were "c" phase. the 5th wire was the neutral. Voltages were 120 to ground on any phase wire, 240 between the wires of "a", 240 between the wires of "b", but about 170 between one of "a" and "b" (120 times 1.41).
Getting two-phase secondaries from three-phase primaries was similar to the above method, only we used a three-phase 120/240 transformer with an auto below it. The three-phase pot had 4 bushings, the two 120 volt legs fed the customer with one secondary phase "a" and the 208 leg fed the auto which produced the other secondary phases "b"
Taking rotation on these services was interesting, to say the least. These services fed old two-phase motors (mostly elevators) and 120 volt lighting.
The phase relationship was 180 degrees apart as opposed to three phase which is 120 degree apart.
05-31-2006, 11:11 AM
I haven't worked on a wierd system but I've run across plenty of oddball equipment on a regular system. I've seen square poles from Canada that were set in the 1950's, steel #4 wire that was put up during World War II when they couldn't get copper, oil filled pole mounted 3 phase 15kv switch with a light switch control at the bottom labeled on-off, and street light controls for the entire road where there was a 120 underbuild run with all the lights on it and a timer at the intersection to connect the underbuild. The steel wire was by far the most "fun" to work, even after 30 years in the air the stuff will try to wind-up on the reel again. If it's cut then it snaps back like a giant slinky into a huge rat's nest of wire. By the way the wire was usually pulled in a 700-800 foot span on dead level ground.
05-31-2006, 12:12 PM
At the steelworks we had our own internal distribution systems including 500Vdc for the cranes and other traction loads, the usual 240/415 AC 50Hz system and high voltage which was both transformed down for local use and used directly by some high voltage motors that operated at a few kV. (Yeah motors!)
05-31-2006, 12:35 PM
25 cycle, Niagara Falls area, (actually Welland) Ontario, Canada. This was a left over from Nicola Tesla days and the power plant at Niagara Falls, on the Canadian side.
When 60 cycle was decided upon as the North American standard apparently in the early ‘50’s, 50 cycles for most of the rest of the world. It was deemed too expensive to rewind the motors for the big machinery and so there are both 25 & 60 cycle lines run in the area. In the industrial plants colors, orange and red, designate the difference at the receptacles and JB’s. I think placards on the X-arms designated the overhead lines.
One of the utilities I worked for as an apprentice still had the voltmeter working on a switchboard, made in Germany in the 1880’s. This was the original voltmeter from the first days of the electrification of the city in the early 1890’s.
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