Re: [time-nuts] Transformer inrush current and transformer simulation
Am 08.06.2016 um 02:31 schrieb Mike Monett: I was not interested in examining the frequency response, saturation effect or core losses. These are only important after the core goes into saturation. I was only interested in the result of switching at the peak or at the zero crossing. This is clearly defined at the beginning of the document. ... The saturation and core losses are outside the scope of the investigation. The investigation was only to examine the effect of switching at the peak or at the zero crossing. This was clearly stated at the beginning of the paper. My analysis correctly defined an unloaded transformer as the only case where switching at the peak or the zero crossing made any difference. This was the goal, and it was met. Saturation is not outside the scope. It is the very heart of the problem. You need to build up a voltage opposite to the grid voltage to keep the current small. That requires an inductance and that requires a core that can be magnetized. If the core is already magnetized to the limit from a previous session, it is as good as simply not there at all. What remains is some meters of copper wire without an appreciable L and that is not enough. I'm haunted by that effect myself on a regular base in that I have a fat class A Krell audio amplifier and it pops the fuse of my living room once in about 5 times of switching it on. I also showed that very few solid state switches were available that switched at the peak, that most vendors simply supply devices that switch at the zero crossing and state to get a model that will accept the surge currents, that switching at the peak could cause severe surge currents with capacitive loads, Nobody uses large transformers anymore, everybody has a diode bridge , capacitor and a DC/DC behind it. Then zero voltage switching makes sense. and that I could not find any reference that stated switching at the peak would not cause core saturation. I provided references that zero voltage switching leads to saturation, and so did others. Your comments offer no additional information regarding the advisability of switching at the peak or the zero crossing. The information you do supply is irrelevant to the problem, and mostly irrelevant to LTspice. you are right. This is not a LTspice problem but your modelling problem. > Attila Kinali It is upon moral qualities that a society is ultimately founded. All the prosperity and technological sophistication in the world is of no use without that foundation. You need to consider getting new sigs. The two you post have little or nothing to do with timenuts, and I'm sure everyone has them memorized by now. OMG , I'm not Attila, but I may need a special time nuts .sig! regards, Gerhard -- Es ist schon alles gesagt worden, aber noch nicht von jedem. (Valentin) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Transformer inrush current and transformer simulation
> OnFri,03 Jun 2016 12:37:26 -0400"Mike Monett" > wrote: >> I found a significant error in the LTspice analysis. I was >> wondering how the current could jump instantaneously at zero when >> the voltage is applied at the peak. That violates magnetism. >> It turns out it doesn't. When LTspice starts an analysis, it >> first calculates the operating point. For the Sine voltage source >> at 90 degrees, it applies the full voltage across the load. In >> this case, it was 169.7V across 1 ohm, resulting in 169.7 Amps. >> That is what was plotted, and is a significant error. > Actually, spice (the engine behind LTspice) does a DC analysis > before almost all modes of operation. This DC analysis has the > intention to start the circuit from a steady-state point and thus > to reduce simulation time. In order for this to work properly, you > have to specify the DC voltage and currents for all sources > correctly. Spice messes this up at times making the first part of > a transient simulation worthless (it has even worse problems when > you do an AC analysis). Additionally LTspice hides too much of > these small complications for the problems to be visible to the > untrained eye and also at times makes it harder to provide the > correct values. Thus, caution is advised. After starting with Intusoft in 1985, moving to Microcap in 1991, having a brief fling with PSpice around 1998, and switching to LTspice in 2006, I can say LTspice has the easiest and fastest data entry of any SPICE program I have tried. There is no problem with specifying the sources in LTspice. Nothing is hidden. The setup menus are extremely easy to view and understand. If you wish, you can have the input parameters displayed on screen, as I have done with two of the functions. LTspice checks all the information given, and if it detects an error it generates an error message and won't run. My original problem was not the setup menus. It was picking the wrong model. > The general rule of "Never trust a simulation you haven't forged > yourself" applies. Most people would be hard put to do a hand simulation of a wideband op amp in a closed-loop feedback network. That is what SPICE is for. >> Out of 13 examples I analyzed, I found only one that involves >> unloaded transformers. >> I found many references that discuss transformer inrush current >> caused by core saturation. This is a serious problem as it puts >> stress on the components and reduces operating life. > I only had a quick glance at your webpage, but it seems that you > used the standard LTspice transformer model. Unfortunately, this > is not a good model to study this kind of behaviour. For one, the > only loss considered in the model is the winding coupling, it > doesn't even directly consider resistive losses in the windings. You would be advised to learn LTspice as it would save you a great deal of misconceptions about how it works. The winding resistances are included in the inductor model. You specify them as needed. I usually used a series resistance of 1 Ohm, but changed it in some examples to suit the application. You can also specify the parallel winding capacitance and resistance. > In this case, the two most important effects that you need to > include are saturation and core losses, which are both frequency > dependent. The cores of electric machine transformers are very > poor when it comes to their "high" frequency behaviour. Where high > frequency starts somewhere closely above mains frequency. Ie 1kHz > is already so far off that somewhere around 90% of the energy > would be dissipated in the core. I was not interested in examining the frequency response, saturation effect or core losses. These are only important after the core goes into saturation. I was only interested in the result of switching at the peak or at the zero crossing. This is clearly defined at the beginning of the document. > The sharp rise in voltage and the leading inrush current have > frequency components that are way higher than mains frequency. > Hence the linear model you used will give inaccurate results, to > put it mildly. > Unfortunately, building an accurate transformer model in spice is > not easy and depends on higher order functions that might or might > not be available in the flavour you use. Not to mention that you > will need to have good (measured) numbers on the non-ideal > behaviour of a transformer, which are also not easy to get by. The saturation and core losses are outside the scope of the investigation. The investigation was only to examine the effect of switching at the peak or at the zero crossing. This was clearly stated at the beginning of the paper. My analysis correctly defined an unloaded transformer as the only case where switching at the peak or the zero crossing
Re: [time-nuts] Transformer inrush current and transformer simulation
Don't let the start of the simulation be the power on time. Best to set up the AC mains volts at zero volts for a half second then go up to 120 VAC. So you actually simulate the power switch. The time before the start of the run is not defined Also you should Google "spice transformer model" and see how others have done it. You will need to add some extra inductors and series resistance. As you found the Spice model does not have magnetics in it. It is simply a pair of coupled inductors. On Fri, Jun 3, 2016 at 10:40 AM, Attila Kinali wrote: > On Fri, 03 Jun 2016 12:37:26 -0400 > "Mike Monett" wrote: > >> I found a significant error in the LTspice analysis. I was wondering how >> the current could jump instantaneously at zero when the voltage is applied >> at the peak. That violates magnetism. >> >> It turns out it doesn't. When LTspice starts an analysis, it first >> calculates the operating point. For the Sine voltage source at 90 >> degrees, it applies the full voltage across the load. In this case, >> it was 169.7V across 1 ohm, resulting in 169.7 Amps. That is what >> was plotted, and is a significant error. > > Actually, spice (the engine behind LTspice) does a DC analysis before > almost all modes of operation. This DC analysis has the intention to > start the circuit from a steady-state point and thus to reduce simulation > time. In order for this to work properly, you have to specify the DC voltage > and currents for all sources correctly. Spice messes this up at times > making the first part of a transient simulation worthless (it has even > worse problems when you do an AC analysis). Additionally LTspice hides > too much of these small complications for the problems to be visible to > the untrained eye and also at times makes it harder to provide the correct > values. Thus, caution is advised. > > The general rule of "Never trust a simulation you haven't > forged yourself" applies. > > >> Out of 13 examples I analyzed, I found only one that involves unloaded >> transformers. >> >> I found many references that discuss transformer inrush current caused by >> core saturation. This is a serious problem as it puts stress on the >> components and reduces operating life. > > I only had a quick glance at your webpage, but it seems that you used > the standard LTspice transformer model. Unfortunately, this is not a > good model to study this kind of behaviour. For one, the only loss considered > in the model is the winding coupling, it doesn't even directly consider > resistive losses in the windings. In this case, the two most important effects > that you need to include are saturation and core losses, which are both > frequency dependent. The cores of electric machine transformers are very > poor when it comes to their "high" frequency behaviour. Where high frequency > starts somewhere closely above mains frequency. Ie 1kHz is already so far off > that somewhere around 90% of the energy would be dissipated in the core. > The sharp rise in voltage and the leading inrush current have frequency > components that are way higher than mains frequency. Hence the linear model > you used will give inaccurate results, to put it mildly. > > > Unfortunately, building an accurate transformer model in spice is not > easy and depends on higher order functions that might or might not be > available in the flavour you use. Not to mention that you will need > to have good (measured) numbers on the non-ideal behaviour of a transformer, > which are also not easy to get by. > > > Attila Kinali > > -- > It is upon moral qualities that a society is ultimately founded. All > the prosperity and technological sophistication in the world is of no > use without that foundation. > -- Miss Matheson, The Diamond Age, Neil Stephenson > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] Transformer inrush current and transformer simulation
On Fri, 03 Jun 2016 12:37:26 -0400 "Mike Monett" wrote: > I found a significant error in the LTspice analysis. I was wondering how > the current could jump instantaneously at zero when the voltage is applied > at the peak. That violates magnetism. > > It turns out it doesn't. When LTspice starts an analysis, it first > calculates the operating point. For the Sine voltage source at 90 > degrees, it applies the full voltage across the load. In this case, > it was 169.7V across 1 ohm, resulting in 169.7 Amps. That is what > was plotted, and is a significant error. Actually, spice (the engine behind LTspice) does a DC analysis before almost all modes of operation. This DC analysis has the intention to start the circuit from a steady-state point and thus to reduce simulation time. In order for this to work properly, you have to specify the DC voltage and currents for all sources correctly. Spice messes this up at times making the first part of a transient simulation worthless (it has even worse problems when you do an AC analysis). Additionally LTspice hides too much of these small complications for the problems to be visible to the untrained eye and also at times makes it harder to provide the correct values. Thus, caution is advised. The general rule of "Never trust a simulation you haven't forged yourself" applies. > Out of 13 examples I analyzed, I found only one that involves unloaded > transformers. > > I found many references that discuss transformer inrush current caused by > core saturation. This is a serious problem as it puts stress on the > components and reduces operating life. I only had a quick glance at your webpage, but it seems that you used the standard LTspice transformer model. Unfortunately, this is not a good model to study this kind of behaviour. For one, the only loss considered in the model is the winding coupling, it doesn't even directly consider resistive losses in the windings. In this case, the two most important effects that you need to include are saturation and core losses, which are both frequency dependent. The cores of electric machine transformers are very poor when it comes to their "high" frequency behaviour. Where high frequency starts somewhere closely above mains frequency. Ie 1kHz is already so far off that somewhere around 90% of the energy would be dissipated in the core. The sharp rise in voltage and the leading inrush current have frequency components that are way higher than mains frequency. Hence the linear model you used will give inaccurate results, to put it mildly. Unfortunately, building an accurate transformer model in spice is not easy and depends on higher order functions that might or might not be available in the flavour you use. Not to mention that you will need to have good (measured) numbers on the non-ideal behaviour of a transformer, which are also not easy to get by. Attila Kinali -- It is upon moral qualities that a society is ultimately founded. All the prosperity and technological sophistication in the world is of no use without that foundation. -- Miss Matheson, The Diamond Age, Neil Stephenson ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
