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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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Generator harmonics question(s)
Years ago I adjusted a neighbor's generator so that it put out 60 cycles at 120 volts. I used a TEK 465B 'scope to look at the frequency. I saw the major 60 cycle waveform and then a lot of smaller waveforms at higher frequencies. I was told that these harmonics were typical of small generators. Today I am replacing the voltage regulator on a small generator and adjusting the governor. I expect I will see the same thing as with my neighbor's generator. Looking inside the generator all I see is rotating coils inside a stationary coil. The rotating coils are energized with DC from the voltage regulator. Looking at old power plant pictures and video it looks as if those giant generators were built the same way. And many of them are still in use today. But I know that the sine wave from the wall has been very good for almost since, if not since, the first generator installation at Niagara Falls. So how do they get the good clean AC from these big generators? Or maybe it's not so clean and is instead filtered. If so how is this done? And can I do this myself without too much effort? Is the effort even worth it? Until the voltage regulator failed on my generator it ran my stuff at home just fine. The fridge, freezer, lights, phone and router. I didn't try any computers. So maybe I don't need to even consider filtering the generator output. But I do see a lot of generators that advertise "pure sine wave output" from an inverter that is part of the generator electronics. So maybe a pure sine wave is important for some electric or electronic stuff. Clocks for example. Anyway, thanks for reading. And for any answers too. Cheers, Eric |
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Generator harmonics question(s)
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#4
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Generator harmonics question(s)
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#5
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Generator harmonics question(s)
On Mon, 27 Nov 2017 14:31:49 -0600, Jon Elson
wrote: wrote: So how do they get the good clean AC from these big generators? Those big power house alternators have more slots in the stator. The winding pattern is set up such that the middle of the magnetic pole has more turns, due to ovelapping sets of coils, than the ends of the pole. This creates the proper wave shape. Smaller alternators can't have as many slots, and thus separate coils, so the induced waveform has some "jumps" anf "flat spots" in it. Until the voltage regulator failed on my generator it ran my stuff at home just fine. The fridge, freezer, lights, phone and router. I didn't try any computers. So maybe I don't need to even consider filtering the generator output. Right, the inductance of typical motors smooths out the small imperfections in the voltage wavem and you pretty much get a sine-wave current. But I do see a lot of generators that advertise "pure sine wave output" from an inverter that is part of the generator electronics. So maybe a pure sine wave is important for some electric or electronic stuff. Clocks for example. Well, some inverter generators produce horrible square waves or stepped approximations of sine waves, that might cause problems for a variety of equipment. Running clocks off the typical generator will be a waste of time, the frequency control will be awful. Jon Thanks for the reply Jon. Do you think Tesla's generators at Niagara Falls were made the way you describe? I wouldn't be at all surprised. Eric |
#6
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Generator harmonics question(s)
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#7
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Generator harmonics question(s)
On Monday, November 27, 2017 at 6:30:13 PM UTC-5, Jon Elson wrote:
Also, in the early days, they ran the alternators off steam engines, and the AC had a definite pulsation with each stroke of the piston. Jon I would have thought they'd be using a nearly infinite mass flywheel to stave off power pulses. |
#8
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Generator harmonics question(s)
On Monday, November 27, 2017 at 7:03:48 PM UTC-5, John-Del wrote:
On Monday, November 27, 2017 at 6:30:13 PM UTC-5, Jon Elson wrote: Also, in the early days, they ran the alternators off steam engines, and the AC had a definite pulsation with each stroke of the piston. Jon I would have thought they'd be using a nearly infinite mass flywheel to stave off power pulses. We had a power plant on site with huge diesel generators, low speed (300 rpm). They did have huge flywheels. I never knew how clean the power was. They were built to power an entire block of buildings, but by this time they were peak shaving only, and have since been scrapped. Very impressive, the floor shook when they ran. |
#9
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Generator harmonics question(s)
On Mon, 27 Nov 2017 17:32:43 -0600, Jon Elson
wrote: wrote: Thanks for the reply Jon. Do you think Tesla's generators at Niagara Falls were made the way you describe? I wouldn't be at all surprised. Eric Everything made since about 1890 had some scheme to control the harmonic problem. The first alternators had "salient poles" on the stator, which were just blocks of stacked steel laminations with coils wound on them. But, even with these, it was possible to shape the rotor flux field to minimize the harmonics. Later, they went to slotted stator lamination sections that made it possible to have coils that spanned several slots, and this made harmonics much smaller. Also, in the early days, they ran the alternators off steam engines, and the AC had a definite pulsation with each stroke of the piston. Jon Greetings Jon, Do you know how the harmonics were measured? Did they use an oscillograph? I am amazed by how much good science was done with such relatively simple instruments. And by how much was discovered and figured out when many measurements took so long and then doing the math that also took so long. Eric |
#10
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Generator harmonics question(s)
John-Del wrote:
On Monday, November 27, 2017 at 6:30:13 PM UTC-5, Jon Elson wrote: Also, in the early days, they ran the alternators off steam engines, and the AC had a definite pulsation with each stroke of the piston. Jon I would have thought they'd be using a nearly infinite mass flywheel to stave off power pulses. The alternator, itself, was a big flywheel. But, with a several hundred HP steam engine with just one cylinder per pressure stage, the power pulses would be pretty strong. They did often put an additional flywheel in the system, but they were NOT infinite. Jon |
#11
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Generator harmonics question(s)
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