Nice displays! But man those voltage waveforms look distorted. Is that actually what your grid looks like or is that an artifact of the way you sense them?
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Re: ICPA
Submitted by Robert Wall on Mon, 18/01/2016 - 12:39.
There's a very well saturated transformer somewhere not far away!
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Re: ICPA
Submitted by _tsalwach on Mon, 18/01/2016 - 14:05.
Hmm...
I saw this earlier, but I did not consider this as big problem (looking how distorted currents can be).
Transformers are certainly not things that I know lot about, but I did not think that loading one with 2,4 kOhm would saturate even that small one.
I've just done some pictures using old analog oscilloscope and they confirm a problem with transformers. But grid waveform also look some "trianglish" to me.
I've changed one of voltage dividers from 2,2k , 220 to 10k , 100k (orange plot), and don't notice any difference.
Please help.
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Re: ICPA
Submitted by Robert Wall on Mon, 18/01/2016 - 17:21.
If you look at the reports on the ac adapters in Resources > Building Blocks, you'll see the same effect starting in those when the input is at 253 V, and it almost completely disappears at 185 V.
It is a matter of how much flux the designer wanted in the core, and the distortion will actually get less as you put more load on the transformer.
In those pictures, you can also see "flat topping" which we get in the UK - allegedly due to the current pulse that all the bridge rectifier circuits draw as they charge the reservoir capacitor.
I saw this earlier, but I did not consider this as big problem (looking how distorted currents can be).
Actually, it's almost the opposite. If you're seeing distortion in your Current signal (and we all do) then it's more important than ever that your Voltage waveform is perfect match to the grid Voltage waveform (both in shape and phase). If you inadvertently introduce harmonics into your Voltage waveform, then you risk counting any corresponding harmonics in the Current waveform as Real Power, rather than as Distortion Power, and in most places we get charged for Real Power but not for Distortion Power.
You can see in your Phase 1 numbers you've got more Distortion Power than Real or Reactive; I calculate it to be about 58 VAR. And a slight nit-pick: it looks like your final column labeled "cos φ" is calculated as Real/Apparent. It's probably more correct to call that "Power Factor'. If you really want "cos φ" then you could do a
cos(tan-1(Reactive/Real))
I've seen that sometimes referred to as fundamental power factor, although even that name is somewhat misleading because it's based on the assumption that you have no distortion at all in your Voltage signal. So "fundamental" kinda' means any frequencies that exist in both V and I. Even on the flat-topped V signals we see around this forum, the coefficients for the harmonics in V are tiny and the true fundamental frequency really dominates.
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Re: ICPA
Submitted by _tsalwach on Mon, 18/01/2016 - 22:01.
I found a contact today to some current transformer guru and he told me exactly the same as You above. My transformers are saturated and I should lower the voltage. Those transformers draw only 4,25mA at 240V so it should not be a problem to build a voltage divider. One day...all about transformers :)
I will change cos to PF, thanks.
Do You think of some feature I can add to this project?
Re: ICPA
Nice displays! But man those voltage waveforms look distorted. Is that actually what your grid looks like or is that an artifact of the way you sense them?
Re: ICPA
There's a very well saturated transformer somewhere not far away!
Re: ICPA
Hmm...
I saw this earlier, but I did not consider this as big problem (looking how distorted currents can be).
Transformers are certainly not things that I know lot about, but I did not think that loading one with 2,4 kOhm would saturate even that small one.
I've just done some pictures using old analog oscilloscope and they confirm a problem with transformers. But grid waveform also look some "trianglish" to me.
I've changed one of voltage dividers from 2,2k , 220 to 10k , 100k (orange plot), and don't notice any difference.
Please help.
Re: ICPA
If you look at the reports on the ac adapters in Resources > Building Blocks, you'll see the same effect starting in those when the input is at 253 V, and it almost completely disappears at 185 V.
It is a matter of how much flux the designer wanted in the core, and the distortion will actually get less as you put more load on the transformer.
In those pictures, you can also see "flat topping" which we get in the UK - allegedly due to the current pulse that all the bridge rectifier circuits draw as they charge the reservoir capacitor.
Re: ICPA
I saw this earlier, but I did not consider this as big problem (looking how distorted currents can be).
Actually, it's almost the opposite. If you're seeing distortion in your Current signal (and we all do) then it's more important than ever that your Voltage waveform is perfect match to the grid Voltage waveform (both in shape and phase). If you inadvertently introduce harmonics into your Voltage waveform, then you risk counting any corresponding harmonics in the Current waveform as Real Power, rather than as Distortion Power, and in most places we get charged for Real Power but not for Distortion Power.
You can see in your Phase 1 numbers you've got more Distortion Power than Real or Reactive; I calculate it to be about 58 VAR. And a slight nit-pick: it looks like your final column labeled "cos φ" is calculated as Real/Apparent. It's probably more correct to call that "Power Factor'. If you really want "cos φ" then you could do a
cos(tan-1(Reactive/Real))
I've seen that sometimes referred to as fundamental power factor, although even that name is somewhat misleading because it's based on the assumption that you have no distortion at all in your Voltage signal. So "fundamental" kinda' means any frequencies that exist in both V and I. Even on the flat-topped V signals we see around this forum, the coefficients for the harmonics in V are tiny and the true fundamental frequency really dominates.
Re: ICPA
I found a contact today to some current transformer guru and he told me exactly the same as You above. My transformers are saturated and I should lower the voltage. Those transformers draw only 4,25mA at 240V so it should not be a problem to build a voltage divider. One day...all about transformers :)
I will change cos to PF, thanks.
Do You think of some feature I can add to this project?