Ebay scope. Not that crisp.
Well I can certainly see why you’re not seeing the under-readings with that signal, it’s way better than I see. It remains a mystery. At this stage I think maybe @philb’s theory is the best we have.
The kink in your Input_4 image above seems much worse than either of those on the scope, or is it just an optical illusion because there’s a V to compare against?
I’m not following sorry?
I cleaned the mating core surfaces and clamped them shut.
I was on the other line with Trystan and he was asking me to check the mechanical aspects of the CT. Meanwhile you wanted a picture on the scope, so that’s what I took. Here are the IoTaWatt traces:
So you are suggesting the extra clamping force holds the split ferrite together better and reduces saturation? That would likely be enough to explain the differences in your results vs @dBC.
Have all your results been using this setup, or is it a new thing? Not the most practical of setups in a switchboard, kind of negates (an then some!) the benefits of the smaller physical size of these CT’s.
The plot thickens. I just went over my numbers and found an error. Over the last week or two I’ve gone through the IoTaWatt phase correction algorithms to increase accuracy. I had spent a day recalibrating my collection of representative CTs, but didn’t do the SCT006. So I just checked it for reasonability against the VT (I’ll check the full spectrum against the AC line tomorrow). The VT has a 1.8deg net lead, and I measured the SCT006 at about 1.08 relative to that at about 4 amps. It’s a little higher as the current increases so I set it to 3 as a happy medium. Now the net between the CT and VT id about 1.2, and that’s what is corrected.
Results are much better. Up to about 15 Amps, they pretty much match the SCT013 watt for watt. Here’s the 20.1 amp case:
So with my CTs, properly phase corrected, I’m getting about 0.7% low. This doesn’t explain any of the saturation point questions, but it does explain why with perfectly good waveforms IoTaWatt wasn’t getting better results.
I think the solution is going to be for one of us to test the other’s samples. Different results it’s the test protocol, same results it’s the samples.
You think there might be some variation in these things? I received mine from Gwyn, I think about a year ago. They are two of the samples that were sent to him by YHDC. I wonder if he can identify the rest of that batch, and see if they are all different. If the stock doesn’t match the samples, maybe there’s recourse.
That 30A version is being actively advertised on alibaba. Like to try one of those out.
I’m a little confused about where you’re at. Can we go back to your post #2 for a minute please? As I understand it you’ve got 4 inputs measuring the one signal which the Fluke says is carrying 20.2A. Input 4 is distorted and its RealPower is 3.9% lower than Input 1. Do you still have that CT? Can you still replicate that situation?
Yes, I still have both CTs. I can replicate the situation, and the result should be the same plots, but the power inducated by IoTaWatt will only be around 1% less than the sct013s.
As the saturation sets in, there is more shift, and in post 2 the phase correction was set very high, resulting in the larger effect on the real power. With lower values, the ct now matches the sct013 nearly exactly until saturation starts, where it starts to fall off but still less than 1% at 20A.
Understand that the plots are still of the raw data. The shift correction happens after when the samples are processed.
There are four CTs connected and they are all clamped to the same 8 wire shrink tubed bundle of primary wire. The Fluke meter is in series with the incandescent light bulb load on the primary.
The IoTaWatt doesn’t directly report current. What you see in the shots as PrimaryA is an output I defined that simply divides power by voltage. As the power factor falls at saturation and the real power becomes less than apparent power, that number might fall by .1 or so. The true current is the Fluke x 8. I did double check by doing an rms calculation on the data points in the plot. The rms amps match the meter x 8.
The clamping of the CTs was only during that later set of pictures and explained what was going on then. The latest numbers with calibrated phase correction are without the clamps, although there does still seem to be a little residual improvement, probably from cleaning the mating surfaces of the CTs.
I’m trying to work out whether the difference is we’re just seeing different amounts of distortion or whether we’re processing it differently. It’s hard to tell just eyeballing your distorted Input_3 input_4 in post 2, to my 60Hz 20A distortion plot which you can see in this post.
Could you attach the raw sample pairs for both the Input_3 and Input_4 plots of your post 2 above please? That will give me a distorted one and a not distorted one as a reference. I should then be able to compare your CT distortion levels with mine.
Yeah, Id have to recreate that. I was pasting into the same spreadsheet destructively. Look, the distortion in your scope trace is pretty self-evident. I have no reservations about your competence to produce a 20A primary and measure it on the scope and I’m not questioning that. I hope you have the same feeling about my data, and the picture from my scope. I know in the past you have questioned my ability to collect a viable set of samples. That’s not a discussion I want to have.
Given three traces, one with visible distortion and two with marginal, I think at this point the CT’s themselves are in question. My point above was that YHDC seems to have made changes to this line over time and it’s not out of the question these CTs are just different. The practical solution, to my mind, is to get to the bottom of that.
Beyond that is the question of what effect 50Hz has. It’s important to understand that, and I’ve been remiss to ignore the issue until now. I’ve taken action and have a 230V 50Hz platform and I’ll get on that posthaste.
If you could please, I think it would be really helpful.
SCT006.ods (100.5 KB)
Load is like 20A now. What can I say, I’m using light bulbs and the voltage is down today. Probably better to match your precision 20A tester anyway.
Thanks. Yes, unfortunately that one doesn’t show any significant distortion at all. What I’m after are two captures one from your Input_3 CT and one from your Input_4 CT like you had in post 2 above. I’m trying to compare your distorting CT with your non distorting CT… even if you have to bump up the current a bit to get there. I appreciate it’s not so easy when you’re at the mercy of the grid voltage.
There are two pages in that spreadsheet. One has distortion “green” and the other not “Red”
Oops… apologies… my bad. I didn’t see the second page. Perfect thanks.
Too late - here’s a batch at 20.5A. That green one is hanging in pretty well.
SCT006-2.ods (100.3 KB)
Even better thanks. I’ll report back here if I discover anything we didn’t already know from it.
It turns out Input_3 (the good one) is more distorted than I realised by just eyeballing your plots in post 2. If it’s not stretching the friendship too much, could I get you to also capture and post the data for Input_4 (the bad one) when it’s well back from the edge please… ~10A maybe? The exact current doesn’t matter, so long as I know what it is, and it’s well away from the edge.
Then I can compare your worst one with mine, in non-distorted and distorted state.
