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50/60 Hz sine wave distortion

Charles R Patton All Messages By This Member #99445 开云体育 Also one other effect. Simple full wave rectifiers cause symmetrical peak clipping.? The rectifiers recharge on the peak of the voltage waveform to replace the charge drawn out on the average of the power supply output.? Hence a lot of PCs such as in a business environment can be a big EMI generator due to the peak clipping. On 12/14/2024 5:21 PM, Charles R Patton via groups.io wrote: toggle quoted message Show quoted text Andy,? I may have missed a couple of other observations but I would like to mention: 1) In situations with a lot of old fashioned 1/2 wave rectifiers or SCR voltage controls (arc furnaces, electroplating controls, certain PCs and the like) or in particular, simple light dimmers, there is a DC unbalance reflected back to the line transformer source.?? Line power transformers are likely to be running near saturation (it's an economic design choice.)?? The transformer is now non-linear and harmonic mixing will take place.? This effect even shows up in big substation links from ground currents such as Schumann resonances generating modulation side bands. Another example.? I went to a customer site for a problem with our equipment.? They had racks of PCs being turned and off for the start and finish of test sequences.? The surge of too many adjacent test PCs simultaneously coming on coupled with too small wiring, led to PC power supply glitches affecting the test as each test start required the charging of the electrolytic capacitors in the step down power supplies.? A couple of cycles, but more than enough to cause trouble. The turning-on PCs ignored the glitch as they have have delay circuits built in and ignore their own disruptive effect, but already ON PCs were not happy. Thinking back about the past, mercury vapor rectifiers were often in 1/2 wave configurations -- too expensive to wire up full wave rectifiers -- a 4:1 cost. Your linear accelerator may have had a similar problem, needs for a lot of power on a pulse basis.? It may? even have been synchronized to the line as I believe some are to minimize line noise from data capture, Regards, Charles Patton
wn4isx #99446 A real LISN can capture such distorted waveforms because the noisy load is isolated from the line and all the loads downstream. I wrote real because? it's fairly easy to make a decent pseudo LISN for the purposes of RF EMI tests, making a real one requires attention to more variables then I can think of off hand. ? In addition to the precision electrical components, there must be very good symmetry between the Hot and Neutral and near paranoid attention to the wiring. ? TRIAC based light dimmers are amazing sources of distorted AC, the most common turn on at some point in both halves of the 50/60Hz, some LED screw in light bulbs are almost as bad.?? High power VSD [variable speed drives] can also be horrible for messing up the AC waveform. ? And server rooms, Oh Dear God let me never ever have to deal with what they cause! ? One of the worst things about modern electrical distribution is the industry has gone from a single integrated 3 phase transformer to 3 sort of matched standard transformers. The sort of matched can cause serious imbalance between the 3 phases, which can have serious waveform consequences. ? ? Oh and Computerized milling machines can place such weird loads, mess up the waveform so bad, the utility power transformers will go up in smoke. I was at a machine shop, a friend was cutting a small piece for work, it was a hot day, upper 90s, the lights went weird, like they were being fed 30Hz, then blackness and every machine in the shop stopped. The silence was defeaning, until some one ran in "Your power pole is one fire!" Since my car was parked fairly close, I quickly moved it away from any danger. ? The utility billed the company for the lost transformers and harmonic attenuation filters. ? ? ?

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