re: " A 60 Hz transformer is physically smaller than a 50Hz for a given power, but 50 Hz has a lot less line losses we pay for as wasted heat on wiring. " I'd like to see a cite on this, or lacking a credible cite, a really good technical explanation (keep the 'hand waving' to a minimum) ...
Chew on this (and learn some of the history of the development of the induction motor): The sorry commercial state of the induction motor languished until 1891 when Maschinenfabrik Oerlikon of Zurich and AEG of Germany demonstrated 20 and 100 horsepower induction motors, a far cry from Tesla's fractional horsepower fan motor and Scott's 3 and 10 horsepower motors. The engineers responsible for the 20 and 100 horsepower machines were Charles E. L. Brown and Michael von Dolivo-Dobrowolsky, respectively. Brown and Dobrowolsky's success was a result of experimentation dating back to the mid-1888s after Dobrowolsky learned of Tesla's work. During these experiments Dobrowolsky invented a special “squirrel-cage” rotor made up of copper bars running through an iron rotor stack. The bars were short-circuited together by a ring at each end of the rotor, akin to Tesla's aforementioned shortcircuited rotor coils. Other improvements came from the use of three phases instead of two, distributed windings in stator slots as opposed to salient poles ... Gee, I wonder _why_ the move was made to three phases from two phases? Could it have been the improvement in efficiency? Self-starting in the desired direction maybe? Above excerpted from: "Comparison of methodologies for induction motor design" http://digitool.library.mcgill.ca/webclient/StreamGate?folder_id=0&dvs=1534515963949~965
What has the above to do with this: "It's called two phase. Period. " There is no question that three phase is superior to two phase. Where did I say or imply that it wasn't?
Really someone has to explain it to you? You should already know this being a ham as it is extremely basic electric fundamentals 101. Common sense should tell you this. Ever seen the difference between a 30 Amp Boat Anchor DC Power Supply and Switch Mode Power Supply? It is about 20 pounds of difference and 6 times the volume. Please ask why is it different? Because the Boat Anchor DC power supply transformer is made for 60 Hz, and the SMPS transformer operates in KHz. The lower you go in Frequency requires more Inductance in your transformers. More Iron and Wire period. As for the cost again is very basic series RL circuit impedance which I am not going to explain to you because you should already know it. Give you a hint. Utilities use High Voltage DC for Transmission. Why use DC? Because it saves the utilities billions of dollars in line losses.
Very true, but they did not make the mistake of using 60 Hz and lower voltages. Yep UK uses grounded circuit conductors, but that is a financial decisions. Besides you know this, I don't have to explain AC power to a Sparky.
The advantage of DC for long line HV is not only lower impedance in and of itself. It also allows for higher voltages, like a million, which further decreases line losses. In addition to that, DC allows AC grid sections to be interconnected without concern of phase synchronization. The rectification process for the conversion from AC to DC and back is done with some pretty amazing equipment.
From what I understand, using a grounded system allows for the use of RCD's which is their equivalent to our GFI and GFCI devices. Having effective ground fault protection is safer, which is less costly in the long run, so I guess 'financial decision' would be correct in a sense. I have worked in an old building with an ungrounded delta and it was scary. The first fault would make a change in a pattern of three light bulbs which were only visible from about 20 feet away in a 100,000 plus square foot factory. That factory had a hot 480 running around 500-519 volts. A fault in that system gave the full L-L voltage from line to ground. Fault #2 would be fireworks. I will take a solidly grounded system over an ungrounded system any day when it comes to working on them.
It has everything to do with money. Both utility and customer. Nothing simpler and cheaper than donding one conductor, and slapping a OCPD on the ungrounded circuit conductors. Utilities get to use dirt as a free conductor, and customers do not need expensive GFD at their homes. Well I understand your fear, but unfounded IMO. Guess it depends on what your background is. Industrial electricians are scared of Grounded Systems. Grounded System by there very nature and design are: Dangerous. Touch a circuit conductor in a grounded system (assuming you are grounded) and you are electrocuted and possible dead with high voltage. Delta system you can get away touching a circuit conductor in a small 208 system. Otherwise cable capacitance can get you. Delta is no more dangerous to work on than a grounded system. Prone to unnecessary outages. Have a ground fault on any circuit conductor, and the OCPD trips, lights go out unnecessarily. Have a ground fault on Delta system, nothing happens except a warning light comes on and alerts maintenance personal to schedule a shutdown to locate and repair fault. That is one of the main reasons industry uses ungrounded delta power. Can you imagine the expense and dangers of an unnecessary outage at a oil refinery, glass extrusion, pharmaceutical, smelter plant, or any industry with continuous processing? Noise noise, noise. Grounded systems are noisy by design and nature. In my younger days I helped on a couple of recording studio designs very similar to what I have done in Data Centers. We used Balanced Power per NEC 647. 120/60 three-phase. Got rid of all that nasty Neutral conductor altogether. Today that is not needed in AV, data, and telecom once they wised up and got rid of using Grounded Signal Transmission topology. Today is all either Balanced Digital or Fiber.
Actually, I came through the industrial apprenticeship and worked on industrial projects for the first 5 years of being in the construction trade. I guess it's a matter of familiarity. We always worked on grounded systems and that is what 90 percent of our training was about. Ungrounded deltas are very rare around here. I don't disagree with anything you have said. Perhaps the fact that there was no true monitoring of the warning lights was also a bit disconcerting. They were up on a bus bar and not visible until you were almost underneath them and they were in a relatively untraveled area. It was out of my comfort zone.
No gain there in voltage, AC voltages can run as high as DC. True HVDV runs at 1 million volts line to line, but it is bi=polar +/- 500 Kv with respect to ground, but 3-phase 750Kv is common. For transport the savings are in lower impedance which is a poor use of words on my part because there is technically no Impedance in a DC Power circuit. Pure resistance. Not certain, but I think I worked on one of the first HVDC interconnects back in 1981 to 1984 period when I worked for PSO in Oklahoma who was owned by Central and Southwest. Today is called AEP. Anyway the great state of TX is an island with respect to the USA grid. All interconnects with TX by law are DC only. Back in the early 80's CSW installed some of the countries first HVDC Utility Interconnects. CSW owned and operated 5 utilities and 4 were in TX which we interconnected with out of state utilities at several locations around the TX border. Today all the USA 8 grids are interconnected by DC only in non published locations. All those wind and solar farms are DC interconnects.
Agree and understand. I am from the Industrial and Commercial side of the house. Sounds like an older system, just a guess on my part. But two parts of the code have not changed. 1. All that is required is a monitoring system to detect a ground fault. As a former utility worker we are trained to look at the 3 Light Bulbs as soon as you enter a Sub-Station. All 3 dimly lit is OK and safe. 2 Bright lights and and one dark light you know you had a fault. The light bulbs are the alarm and visual indicators. 2. Ungrounded Systems require qualified personal to work on. But if you stop and think about what I said, then you understand why industry uses 3-phase delta. No tonly becaus eof the power levels involved, but also because it is a lot tougher system and more resilient. That darn squirrel cannot knock your plant off line.
DC requires less insulation capacity for a given RMS value than AC. Insulators have to handle the PEAK ac voltage, while DC insulators only have to handle the RMS. This is a significant difference when you're running really high voltages (500k+), where you're on the verge of corona even with the longest insulators available. There is also a TINY amount of radiation loss at AC that you don't have at DC...though this only shows up when you have conductors a few hundred miles long.
In the Niagara Falls area they originally installed a 25hz system! This system was still used in downtown Buffalo for many years....long after the 25hz generating equipment was retired. The Niagara Mohawk Power Company ( who I worked for when directly out of college) actually had to install 25hz conversion equipment in order to serve all the 25hz customers in older downtown Buffalo. The 25hz transformers and motors were huge compared to 60hz. Now I do know that 25hz must not have been a resounding success because the country adopted 60hz. Why not 50hz? I can't say for sure but devices with iron cores (transformers and motors) had lower iron losses and smaller mass when operating on a higher frequency. Somebody must have been thinking about iron mass and losses when deciding on optimizing frequency and did not consider transmission line losses. So they zipped right by 50hz and decided on 60hz? Once 60hz became widely adopted there was no turning back! Having some experience with 400hz systems I became very aware of line losses quickly. If you think 60hz losses are bad try playing with 400hz!
