how a transformer works. Why does a power transformer have high in rush current? When are the losses in the core of a power transformer the highest, at no load or full load and why?
This is not correct.Induced Current principle.
At power on the transformer presents a resistance equivalent to the DC resistance of the winding, just a few Ohms.
Until the inductive reactance effect takes place it then resorts to whatever the Impedance of the primary presents.
The losses in the core are larger when the flux excursions are larger. The flux in the core is proportional to the integral of the applied voltage.When are the losses in the core of a power transformer the highest, at no load or full load and why?
The DC resistance is not the limiting factor if the grid sine wave is applied at the peak (positive or negative) of the sine wave. See the second scope capture above; there is no 180 amp surge in that case. Something other than the DC resistance must have limited the current; what was it?The inrush is categorized during the first cycle where the DC resistance of the primary is the only limiting factor to current.
Well, yes, that's what is shown in the first scope capture above. In fact, I said "I put a current shunt in series with the primary winding (120 VAC here in the U.S.), and disconnected the secondaries from the rest of the circuitry."This will occur without a rectified or loaded secondary.
Max.
If you do a history search on his user name, it appears that he mostly posts these questions in the chat forum. I am used to him asking on the chat forum and I didn't even notice that this thread was in the homework forum.Uhm... you guys do realize that the OP hasn't shown a lick of effort and that all he is doing is sucking your descriptions onto his paper and turning them in, don't you?
That's this guy's mode of operation: bombard the forum with questions he isn't willing to put forth any effort into hoping that someone will come along and eventually give him answers that he can snag as his own.
A few times when I first started hanging around this forum, I was accused of posting homework and just collecting the answers when, in fact, I was just really really curious and in need of a different explanation/perspective.If you do a history search on his user name, it appears that he mostly posts these questions in the chat forum. I am used to him asking on the chat forum and I didn't even notice that this thread was in the homework forum.
His questions somehow don't have the flavor of homework questions, and I'm not sure he's actually in school. Maybe he doesn't pay close attention to what forum he's posting in.
The simple answer in that situation would be not to post in the homework forum. The assumption is that if it's posted in homework then the homework rules will apply.A few times when I first started hanging around this forum, I was accused of posting homework and just collecting the answers when, in fact, I was just really really curious and in need of a different explanation/perspective.
I usually give people the benefit of the doubt in such matters.
Your example shows the opposite of this behaviour. I am curious about this- can you explain why in more detail?This is not correct.
This is also the reason that the surge that occurs is dependent on just where the grid sine wave is when the switch is closed. If the grid sine is just crossing zero, then the surge will be a maximum. If the switch is closed when the grid sine is at a peak, then there won't be any significant surge at all.
One can choose to give the benefit of the doubt or choose to go the other way. The first approach may be softer on the poster's ego, but it may not help them develop the proper attitude. The latter may be a bit harsher, but the barrier to entry is not that great. You were a case in point, IIRC. I believe I was one of those assuming you were just looking for a free handout, but all we ask that anyone do to destroy that assumption is to show some effort and work. In your case, again, IIRC, the assumption that you were looking for a free handout was driven by the fact that you seemed resistant to show that work - not because you were actually looking for a handout, but because you believed that just beeing shown the answer would be sufficient for you to learn what you needed to learn (and it frequently is). But as soon as you figured out (and it didn't take long) that you had to show some effort, you did and were immediately accepted into the fold, so to say.A few times when I first started hanging around this forum, I was accused of posting homework and just collecting the answers when, in fact, I was just really really curious and in need of a different explanation/perspective.
I usually give people the benefit of the doubt in such matters.
This is not correct.
This is also the reason that the surge that occurs is dependent on just where the grid sine wave is when the switch is closed. If the grid sine is just crossing zero, then the surge will be a maximum. If the switch is closed when the grid sine is at a peak, then there won't be any significant surge at all.
When I just now had a look at post #3, the first image had stopped displaying in the body of the post, even though the thumbnail was still there; very strange. I was able to edit and fix the problem.Your example shows the opposite of this behaviour. I am curious about this- can you explain why in more detail?
Ah, I think I get it. So you're saying that switching at the zero-crossing does indeed causes the largest inrush current pulse, but that it is delayed.If you look at the first image in post #3, you will see that the applied grid voltage (green trace) is just passing through zero on the way to the positive peak of the (somewhat distorted) sine wave. About 5 mS later, there is a 180 peak amp surge (purple trace).
Faraday's law tells us that the flux is proportional to the integral of the applied voltage.Ah, I think I get it. So you're saying that switching at the zero-crossing does indeed causes the largest inrush current pulse, but that it is delayed.
So what delays it?
Read thisAh, I think I get it. So you're saying that switching at the zero-crossing does indeed causes the largest inrush current pulse, but that it is delayed.
So what delays it?