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| Help with Pulse Transformer Design |
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| Berni:
--- Quote from: KurtK on August 23, 2019, 09:21:19 am --- --- Quote from: MagicSmoker on August 22, 2019, 09:21:14 pm ---It is immensely frustrating when the OP does not include important details... like that the secondary is high voltage or the average power rating is 50kW. --- End quote --- I sure sense your frustration all the way across the pond. If you look at the graph in my OP you can see the voltages and currents involved. And I couldn't very well calculate average power before I there were some agreement to how it should be done. Also to get to the bottom of something you need to have a dialogue, just like we have now. I can't just present a massive wall of information to being with, that would be highly confusing for the reader as most of it would probably be irrelevant for this topic. --- End quote --- The graph shows no units so this could be kA or nA of current flowing trough it. If we assume they are always base units of A and V then the powers involved are far above 50kW. Additionally if the Y axis is assumed to have only base units then one would assume the X axis also to be in seconds and in that case the pulse duration of the first hump is 15000 seconds long (4 hours) so that would require a transformer designed to operate at 66 microHertz. Such a transformer would likely be the size of a continent at these powers. So this makes one assume the graph is not using base units. So can you explain in what way it was clear from the graph that this is a huge 50kW pulse transformer? I feel like such a thing should be mentioned in the first 5 sentences of the post or even the title. People on forums can only be as helpful to you as much as you are helpful to them in providing the information about your situation. |
| MagicSmoker:
--- Quote from: KurtK on August 23, 2019, 09:21:19 am --- --- Quote from: MagicSmoker on August 22, 2019, 09:21:14 pm ---No, that gives you apparent power as I keep saying. You need to adjust for any phase angle displacement of current with respect to voltage to get true power. --- End quote --- I know you keep saying that, but I still don't understand it. By "instantaneous" I mean "in that given instant"... --- End quote --- A transformer primary exhibits both magnetizing and leakage inductances and current lags voltage in an inductor, right? It doesn't matter what the voltage waveform applied to the primary of a transformer looks like, the current through it will be a time (phase angle) delayed version of it*. * - EDIT - and integrated... forgot that part. In a lossless transformer with finite magnetizing inductance and the secondary unloaded, the only current flowing in the primary will be for magnetizing the core and this is a purely inductive current so it will be phase shifted by 90 degrees from the voltage. This is a measurable current and the voltage is of course also measurable, but if you simply multiplied those two parameters together without accounting for the phase shift you get apparent power, VA, not real power, W. To find real power you have to multiple VA by the cosine of the phase angle displacement which in this case is 0. If this "almost ideal" transformer is loaded on the secondary, the primary current will increase - because of the current reflected from the secondary through the turns ratio - and the phase shift will decrease, because the magnetizing current with its 90 degree phase shift will become a progressively smaller fraction of the total primary current. In a real transformer there are both iron and copper losses, of course, and the iron losses will be fixed for a given applied primary volt*seconds while the copper losses will vary with the square of load current. Hence why I said that actually measuring the efficiency of a transformer is tedious and not typically worth the bother. --- Quote from: KurtK on August 23, 2019, 09:21:19 am --- --- Quote from: MagicSmoker on August 22, 2019, 09:21:14 pm ---This applies whether the transformer is driven by a sine wave from the mains or a square wave from an H-bridge. --- End quote --- And in this case the transformer is driven by a exponential decaying pulse. --- End quote --- Doesn't matter. --- Quote from: KurtK on August 23, 2019, 09:21:19 am ---I sure sense your frustration all the way across the pond. If you look at the graph in my OP you can see the voltages and currents involved. And I couldn't very well calculate average power before I there were some agreement to how it should be done. --- End quote --- Pictures accompanying a post should help illustrate what is written, not substitute for it. Look at all the forums - including this one - where images were hosted on Photobucket or the like and are now no longer available. IMO, it's better to present too much information in the OP than to trickle out details in subsequent replies. --- Quote from: KurtK on August 23, 2019, 09:21:19 am ---If it was only a question of shame, I would certainly do that, in fact I would outsource everything. --- End quote --- You may have misinterpreted me. I could certainly design your transformer but I almost certainly couldn't make it myself - not even a prototype. Thus I would specify the core size and material, number of primary and secondary turns, wire gauges for each, layer stackup and other pertinent details like what UL or EN classification it needs to meet, vacuum impregnation, etc., and then let the transformer manufacturer worry about the rest... like how to wind thick ribbons of copper around the coil former or achieve a 10kV or so functional insulation level. |
| KurtK:
--- Quote from: Berni on August 23, 2019, 11:14:26 am ---So can you explain in what way it was clear from the graph that this is a huge 50kW pulse transformer? --- End quote --- The title of the graph is "voltage and current" usually that means "unless otherwise noted you are dealing with the base units of Volts and Amperes. If you had doubts about that, all you have to do is ask, I'm right here. Yes I could have written that, yes I could have written many things - but I didn't, so I'm sorry. And regarding the X-axis I already made a public apology that I forgot to mention it was nano-seconds, and I will happily apologize again to you; I'm sorry - I forgot, sometimes my short-term memory just doesn't work properly. |
| Berni:
--- Quote from: KurtK on August 23, 2019, 12:55:40 pm --- --- Quote from: Berni on August 23, 2019, 11:14:26 am ---So can you explain in what way it was clear from the graph that this is a huge 50kW pulse transformer? --- End quote --- The title of the graph is "voltage and current" usually that means "unless otherwise noted you are dealing with the base units of Volts and Amperes. If you had doubts about that, all you have to do is ask, I'm right here. Yes I could have written that, yes I could have written many things - but I didn't, so I'm sorry. And regarding the X-axis I already made a public apology that I forgot to mention it was nano-seconds, and I will happily apologize again to you; I'm sorry - I forgot, sometimes my short-term memory just doesn't work properly. --- End quote --- Yeah, its best to make it clear you want a massive power transformer to begin with. According to the graph this involves 500kW peak of instantaneous input power into the transformer. The sort of transformers that will handle this sort of power efficiently are likely going to the the size of a minifridge and too heavy for a single person to move. That being said air core is used for some of these specialty high pulse power transformers since it might indeed be difficult to find the massive ferrite core for one of these. |
| KurtK:
--- Quote from: MagicSmoker on August 23, 2019, 11:20:42 am ---A transformer primary exhibits both magnetizing and leakage inductances and current lags voltage in an inductor, right? It doesn't matter what the voltage waveform applied to the primary of a transformer looks like, the current through it will be a time (phase angle) delayed version of it*. --- End quote --- I'm wondering, could it be that actually are saying the same thing but are talking past each other because you think I'm talking about only multiplying three integers and expecting to the result to be average power? Because that is not what I mean, I'm talking about using numerical methods, also know as Digital Signal Processing? --- Quote from: MagicSmoker on August 23, 2019, 11:20:42 am ---Pictures accompanying a post should help illustrate what is written, not substitute for it. Look at all the forums - including this one - where images were hosted on Photobucket or the like and are now no longer available. IMO, it's better to present too much information in the OP than to trickle out details in subsequent replies. --- End quote --- If I had a stringently defined project with all parameters clearly defined I would have done that, yes. I believe you yanks have a suitable phrase for that "different folks, different strokes" - I can't make everyone satisfied no matter how much I try. But your preferences are duly noted and I will try to accommodate you. --- Quote from: MagicSmoker on August 23, 2019, 11:20:42 am ---You may have misinterpreted me. I could certainly design your transformer but I almost certainly couldn't make it myself - not even a prototype. Thus I would specify the core size and material, number of primary and secondary turns, wire gauges for each, layer stackup and other pertinent details like what UL or EN classification it needs to meet, vacuum impregnation, etc., and then let the transformer manufacturer worry about the rest... like how to wind thick ribbons of copper around the coil former or achieve a 10kV or so functional insulation level. --- End quote --- Great, if you can design the transformer, I can certainly make it or have it made and then we could close this thread, seems like win/win. We are talking about one transformer only for a prototype device so the only standard it has to meet for now is "no arcing", and if it can sustain a few minutes of operation without core meltdown that would be fine too. |
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