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Author Topic: Reactive power - Reactive Generator research from GotoLuc - discussion thread  (Read 362099 times)

Farmhand

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Engineers care about apparent power, because even though the current associated with reactive power does no work at the load, it heats the wires, wasting energy. Conductors, transformers and generators must be sized to carry the total current, not just the current that does useful work.

The above statement makes no sense to me,and seems to be an oxymoron.
Quote:Engineers care about apparent power, because even though the current associated with reactive power does no work at the load, it heats the wires, wasting energy.

Is not heating wires doing work,in the form of creating heat?.This is reactive power doing useful work as far as im concerned.

That's kinda debatable, Some of the reactive power returning to the supply is converted to real power and dissipated as heat in the wires. No one I know of wants the wires hot, so the work is unwanted and not useful. The only useful work is work done on/by or whatever in the intended load we are powering like a motor or a light ect.. Although some people might want to risk heating their house with "reactive power related losses", I'm sure I wouldn't, the less active power in the house wiring the better in my opinion.

Just sayin it depends how it's read and how we chose to think about it. I'm all for experiments. Going by the complexities of accurately measuring AC power in such systems I personally in my own experiments would want to see some other form of verifying things. Not saying using the scope is not good. Proof is in the pudding, and no one can deny when lots of work gets seen to be done obviously over and above the input.

I've got my scope out practicing and familiarizing myself more with it in fact, though I'm not so sure mine will give much useful Math calculations. I'll try on something simple first and see what I can calculate and see if the scope will do the same.

I did check a while back my true RMS meter against the scope and they seemed very close, so with a good battery some DMM's can be quite accurate.

Cheers


tinman

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OK, I checked the screen on the video and it does not indicate AC coupling by the usual squiggle. Very tricky; there doesn't seem to be any way to tell the channel coupling except by going into the setup menu, where we can see that Luc has AC coupling set on both channels. The coupling isn't indicated on the normal scopeshot apparently. That's a "gotcha" that means one needs to be very careful using that particular scope model. As we can see, your higher-end Tek scope indicates clearly the coupling with the sine wave squiggle.

The coupling issue has come up before. Many people seem to think that you need to use AC coupling to measure an AC signal, but as we now know, that's not what it's for at all. Looking at how the scope accomplishes the miracle of AC coupling might help one to understand just what it does and how it's used. AC coupling merely switches in a capacitor in series with the probe input lead, blocking the DC component of any input signal and only letting the AC component pass to the scope's input.

Well it looks like i have made the same mistake. I asumed that as we are measureing AC then it should be set to AC coupling-now i have learned something new. As you can see in my last scope shot's,i have the ac wave next to the ch1 ch2 indicator(bottom right hand corner). So now to go change scope to DC coupling,and start over lol.
Realy wish i could get this math crap worked out on my scope.

tinman

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Below is a picture of the circuit i am testing ATM.The picture represents 1/2 cycle,so as to make it clear what i ment by the FWBR being hooked to the high side of one tank,and the low side of the other tank.

poynt99

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Realy wish i could get this math crap worked out on my scope.
I thought you had it sorted some time ago?

DilJalaay

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Function AC / DC coupling Controller in Oscilloscope
« Reply #439 on: January 06, 2014, 07:12:50 PM »
Function AC / DC coupling Controller in Oscilloscope




tinman

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I thought you had it sorted some time ago?
I have sorted the part where you add channel A and B,and get the math trace up on the screen,but still cant find where to read the result of the sum,other than a whole bunch of numbers that make no sense to me.

poynt99

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Can you post a screen shot of A x B?

Maybe the result is buried amongst all the numbers.

poynt99

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Okay, something new learned!... DC coupling when wanting accurate math results from an AC source.
Not a problem. I will do that from tomorrow on.

Thanks for finding that one.

Luc
Well, you should be using DC Coupling for 99.9% of your scope measurements actually.

gotoluc

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Hi poynt and all,

here is a video update with the scope set to DC coupling. I'm still questioning the channel 2 Inversion.
Can you please confirm which way it is and what is Watts used

Video: http://www.youtube.com/watch?v=gTJ8i5unIwQ&feature=youtu.be

Thanks

Luc

d3x0r

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from a ground base; (common/neutral), the probe on the outside of a resistor is positive for a positive current draw.


 - load(+ side) - battery - (low, negative side, scope common) - CSR - (probe, high level is positive current) - (load)


 Should not be inverted.  Inversion should be used if you're biased against the positive as the ground reference.

barbosi

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Hi poynt and all,

here is a video update with the scope set to DC coupling. I'm still questioning the channel 2 Inversion.
Can you please confirm which way it is and what is Watts used

Video: http://www.youtube.com/watch?v=gTJ8i5unIwQ&feature=youtu.be

Thanks

Luc

In the probe menu as far I can see your probe (which is a voltage probe), you should not chose current probe. Tek has its own current probes and it knows how to deal with their characteristics. While you have your own shunt and measuring voltage across... you get it. same you should not trust agilent current probe on tek, and so on.

Example of a current probe notice the orifice to insert the cable:
http://cdn7.us.yokogawa.com/uploaded/701928_29_5.jpg

From Tek:
http://www.tek.com/sites/tek.com/files/media/image/TCP202DCCoupledCurrentProbe-1-L.jpg

PS: In fact, there are other types of current probes, for IC, etc. Tek will recognize it from the pins on the connector. All pretty expensive. Since you are not looking at the edge of visible spectrum or brain surgery, you can stick with the poor man's tools, shunt & voltage probe.

poynt99

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In the probe menu as far I can see your probe (which is a voltage probe), you should not chose current probe. Tek has its own current probes and it knows how to deal with their characteristics. While you have your own shunt and measuring voltage across... you get it. same you should not trust agilent current probe on tek, and so on.

Example of a current probe notice the orifice to insert the cable:
http://cdn7.us.yokogawa.com/uploaded/701928_29_5.jpg

From Tek:
http://www.tek.com/sites/tek.com/files/media/image/TCP202DCCoupledCurrentProbe-1-L.jpg

PS: In fact, there are other types of current probes, for IC, etc. Tek will recognize it from the pins on the connector. All pretty expensive. Since you are not looking at the edge of visible spectrum or brain surgery, you can stick with the poor man's tools, shunt & voltage probe.

We've been through this already here in this thread, and it was I that was giving Luc a hard time about using a voltage probe as a current probe. But I have tried this on my Tek scope and not only does it work, but I can see no reason why it is not a valid method.

barbosi

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We've been through this already here in this thread, and it was I that was giving Luc a hard time about using a voltage probe as a current probe. But I have tried this on my Tek scope and not only does it work, but I can see no reason why it is not a valid method.

So you determined that a Tek current probe is linear as a 0.1Ohm resistor he is using? Others may not have the shunt like that but rather 700mv@200A. They should know they have to use a different approach.

Or make a standard poorman's procedure, but I may be wrong and all would know how to handle it.

poynt99

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So you determined that a Tek current probe is linear as a 0.1Ohm resistor he is using? Others may not have the shunt like that but rather 700mv@200A. They should know they have to use a different approach.

Or make a standard poorman's procedure, but I may be wrong and all would know how to handle it.
I determined that using a 0.1 Ohm CSR, one can select current for probe CH2, and one can also set the scaling for 100mV/A so that CH2 will read directly in the correct mA.

Yes, the measurement is sufficiently accurate for these measurements at 60Hz. If that CSR was replaced with a good non-inductive resistor, we could do high frequency measurements as well. Actual Current probes are non-intrusive, but they produce a voltage output just as a voltage probe across a CSR does.

gotoluc

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I determined that using a 0.1 Ohm CSR, one can select current for probe CH2, and one can also set the scaling for 100mV/A so that CH2 will read directly in the correct mA.

So poynt, what is your decision on channel 2... Inverted or not Inverted?

Thanks

Luc