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| Understanding three phase line EMI filters |
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| langwadt:
--- Quote from: T3sl4co1l on June 14, 2019, 07:37:26 pm ---Yeah, you wouldn't want to do that for a substantial load, but for a control, to get more reliable power, that would be okay. Makes sense. The problem is neutral currents, which ideally shouldn't be drawn. It's usually a smaller conductor, to handle leftover unbalanced current, not full load. Tim --- End quote --- ? like everyone else around here I have 3 three-phase power, when I use a single phase load like a kettle only one phase and neutral is used so the phases and neutral must be roughly the same size |
| duak:
As long as there are 2 or 3 phases present, there won't be any neutral current. I see the rectifier diodes switching to deliver the highest peak dfferential voltage at any instant. If the load was a bipolar supply with the common center tied to neutral then there could be. But here, the load shouldn't be referenced to neutral. I looked at the app note, and it looks like the author used the ground symbol for circuit common but it doesn't mean it should be connected to neutral - that could be exciting! I've worked with a few 3 phase systems, but they've always had a wye transformer source with the center connection to neutral. There are apparently other PoCo connections, but I haven't seen them. eg., corner grounded delta (2nd image) and high-leg delta (3rd image). I think the circuit above will work fine with these configurations. The only configuration that would cause a problem would be an ungrounded source transformer. Conceivably, there could be higher phase to neutral voltages than phase to phase voltage. It would take a particular failure or wiring mistake but it's possible. Here's a triplen current story: I traced some down in a delta-wye step-down transformer operated as a step-up. If memory serves, the line fuses were 150 A and would occasionally open under load. There was some 50-60 A in the transformer's neutral, even when it was unloaded. It was pretty damn hot too. I disconnected the neutral and all became as it should be. That poor transformer was probably conducting a good bunch of the triplen currents generated in the building. |
| coppercone2:
for understanding the mysterious inductor resistor parallel combo http://ecee.colorado.edu/~rwe/papers/APEC99.pdf The first page explains quite a bit |
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