240 volt with center tap versus 240 L- grounded L. Interested in the history.

[11bgrunt]

I read recently that only the US and Canada use 240/120 volts derived from a 240 volt coil with a center tap. As I look through this forum, similar voltages are in European countries. How did we get to the point where voltage converters are needed as you travel around the world? Why 240/120 and not 200 L-L only or 60/120? Why 60hz and not 50hz as in other countries? This is just about single phase residential. I will always wonder about the three phase and commercial options.
I don't have a good answer and feel like I should.
:?

 

[gar]

150310-2100 EDT

When Edison was working on an electric lighting system, 1879, he understood a number of factors that were necessary to create a practical electrical distribution system.

1. Had to be a parallel system.

2. Maximum power transfer was not the correct design goal.

3. Any one load could be switched on and off without a great affect on other loads.

4. Voltage needed to be as high as reasonable, practical, and safe. About 100 to 110 V was about as high as reasonable in 1879 for a light bulb.

5. To reduce distribution power loss and copper cost the distribution voltage needed to be high. 110 V was practical for the light bulb, but could be doubled for distribution by a three wire system that included a neutral.

6. Generator internal impedance and distribution impedance had to be low for good efficiency.

7. Magnetic design of the generator had to be such that excitation of the field did not produce much magnetic core saturation. Edison and his people discovered iron core saturation.

The same concept of 5 was carried over into our AC system.

60 Hz requires less iron than 50 Hz. 400 Hz is good for aircraft, but too high for our home distribution lengths and higher cost for magnetic materials. We really don't need the weight reduction for something on the ground. Lower frequency is better for very long distribution distances, and therefore, for some of these we switch to DC. But there also has been 25 Hz that requires very much larger transformers. High voltage DC distribution, 1,000,000 V, at this time is really a two point system, source and destination because of cost. Whereas an AC lower voltage distribution system, 345,000 V or lower, is practical with magnetic transformers.

.

 

[Jraef]

Gasp!
You mentioned Edison and Transformer in the same sentence! He would have had you electrocuted for such blasphemy...

When Westinghouse (using Tesla) tried to get the jump on Edison by promoting AC, Edison fought them tooth and nail (old story, discussed frequently, look up the term "War of the Currents"). Little known in that however is that Edison was at the same time quietly INVESTING in AC power systems through his connection with AEG, a German company he had helped found who was ALREADY working on AC to get the jump on the system in Europe that Tesla had made viable here (lots of people were working concurrently on AC generators and motors at the same time, Tesla's was just the first PRACTICAL one). Westinghouse's systems were 25Hz 1 phase at first and 2 phase later at Niagara, but AEG was building a 3 phase generation system with the goal of getting cheap hydro power from the Alps down to Munich for the burgeoning German industrial machine. Because wire was expensive, they came up with the idea of 3 phase over 2 phase because it saved a wire, and 50Hz instead of 25Hz to make the transformers smaller. When Edison realized he was going to lose the battle in the US, he brought over some 50Hz AEG generators, but at the same time, Westinghouse was experimenting with 133Hz and 40Hz, trying to find the right balance, and other European companies like Siemens, Alstom and Brown Boveri were all jumping on the AEG bandwagon to copy what they did at 50Hz. As a board member of AEG, Edison witness the profitability blood bath that ensued when lots of companies started jumping on the 3 phase bandwagon, so he decided to NOT promote 50Hz here, because then the Europeans could get a foothold by already being in production.

So he installed the first AC 3 phase system here in a Southern California (Redlands) pumping station but it was 40Hz. The problem was, he was making his millions selling light bulbs, and 40hz produces a still detectable flicker on his bulbs and he decided on 60Hz so that the flicker went away, but the Europeans could not flood our market with their generators and motors. So the SECOND 3 phase system went in a year later in California near Sacramento (Folsom). Everyone marveled at it and he almost (some say did) steal the thunder from Westinghouse and Tesla, who were forced to follow suit with 60Hz 3 phase or be left behind.

 

[swervontes86]

changing a transformer in a generator to three phase

changing a transformer in a generator to three phase

I recently got a side job hooking up a generator that they pulled off a house so it was single phase they brought it to a scrap yard and are making it a natural gas generator that needs to be changed into three phase to hook up the equipment at the scrap yard a 208v bailer some welders ect ect i took apart the transformer inside the generator and followed the wiring schematics on the diagram to change the generator to 208v was this the correct way to fix this problem?

 

[kwired]

You may be able to set the voltage to 208 but how are you going to derive a third phase without rewinding the main coils?

After posting I realized this is not a new thread but probably should have been, I was replying to post just before mine.