7anoter4 – I appreciate all your contributions on the forums. You provide some of the most detailed calculations around, which is very helpful. I suspect as often occurs in long threads, everyone is saying roughly the same thing, just confused by the fact that so many different people are involved in the discussion and using different terminology. I certainly don’t disagree with anything you said. I don’t think anything that you said contradicts what I said.
7anoter4 said:
I beg pardon from our Electric Power Engineers if I am intruding. But , in my opinion only prc is right
On this particular occasion prc has since revised his thinking (something we all do from time to time).
I apologize again if my "electrical philosophy" provoked such an inconvenient,
never the less it is not clear if it is a "loss" since this reactive power is returned to the source and the source has to overcome this. Active power is always positive. Reactive could be positive or negative. But this is again "philosophy" and I really sorry.
If difference in “philosophy” means difference in “terminology”, then I agree. I explained above the context of the word “loss” 1 Jul 11 13:01 and said that if you object to the word “loss” you are free to use your own term. If you’d like to understand my thought process, then I’d like you to think about filling in the blank:
100mvar flows into the primary winding and 90 mvars flows out the secondary, therefore 10 mvars is ____ in the transformer (and don’t say “lost”). Would “consumed” be better? How about “associated with current flowing in reactive components” (more correct, but a little cumbersome, don’t you think?). You can take your pick and let us know. It really doesn’t matter to me what you pick, and I promise I won’t you’re your term “absurd”. As long as you put the word mvar next to your chosen term, you’d think every power engineer should be able to figure out what you’re talking about, and know that it’s not a watts loss. And if you’re still concerned people might not pick up on that clue, you might even try putting quotes around your chosen term to indicate care is required to avoid misinterpretation of that particular term. But don’t get your hopes up, engineers on eng-tips (myself included) can figure out a remarkably unforeseeable variety of ways to parse/interpret/misinterpet any sentence! ;-). A thermodymamics engineer might object to the use of the term loss to describe even real power, since of course the power is not lost, only transferred. (you knew it meant power lost
from the electrical system, but you didn’t say that, so what other conclusion can the thermodynamics engineer possibly draw other than that you don’t understand the principle of conservation of energy). Sorry, I’m getting a little off track (waxing philosophical).
As far as the positive/negative nature of reactive power lost/consumed/associated with passive reactive elements contrasting with the positive-only real power lost in a passive resistive element, I know you already know the math, but imo it supports the analogy of reactive “loss” in an inductive element: By convention S = V I* which means the S which is lost/consumed/associated in a passive inductive passive device is positive while the S which is lost/consumed/associated in a passive capacitive element is negative. The naturally leads to common terminology where we think of capacitive devices as sources of vars and inductive devices as consumers of vars.
I have an objection in connection with reactive power loss calculation neglecting core magnetic reactance. I think the magnetic reactance could add another 15% to the total reactive power loss
I agree, that is a point I made 29 Jun 11 14:42. My calculation came up with 11% assuming 1% no-load current and 8% leakage reactance. I haven’t read your calc in detail but it seems very simlar to mine. You mentioned (calculated?) breaking the primary and secondary reactances which is something I mentioned but did not do. We both made the same assumption that the reactive magnetizing current is practically the same as no-load current has negligible effect on calculating reactive current from no-load current.
I think everyone agrees there are in most circumstances a variety of calculations from simplest/least-accurate to complicated / most-accurate. Using leakage reactance and neglecting magnetizing effect is the first/simplest estimate. We can try to get more and more accurate as we sharpen our pencil. How productive that is depends on the situation.
I don’t see much difference between what you said and what I said.
Although after composing this long response, I looked back noticed you said “I think the magnetic reactance could add another 15% to the total reactive power
loss”. That just strikes me as funny, given the way I have interpretted your comments. Maybe I misunderstood you and you were not objecting to my use of the term loss in this context?
I hope you don't take anything I said here too seriously. I may have completely misunderstood what you were saying. Again I certainly do respect your knowledge and your contributions, including detailed responses you provided to my question on several occasions.
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(2B)+(2B)' ?
