Hi,
Here is a reference to efficiency of power distribution transformers:
(Attachment Link)
Taken from:
https://documents.hammondpowersolutions.com/documents/Literature/Medium_Voltage_Distribution_Transformers/HPS-Millennium-G-VPI-Brochure.pdf
This is Hammond Power Solutions.
This is only resistive losses, it is not regulation.
Notice how the efficiency improves as at the larger kVAs.
Regards,
Jay_Diddy_B
Oh, and I recall a typical distribution transformer impedance is somewhere around 5%
Impedance is not something that is measured or specified as a percentage.Yeah, technically you're correct
Isn't that pretty much the only kind of correct?
Turning off a couple relatively light, probably actually fairly clean PF-wise loads that are fairly well connected via 14ga/12ga wire to your panel which is then connected via typically 6ga or bigger out to a transformer that is well connected to the grid through a relatively low impedance source, very stiff, with massive fault current capability, won't show much difference, even right at your load.
Oh, and I recall a typical distribution transformer impedance is somewhere around 5%
Impedance is not something that is measured or specified as a percentage.
Impedance is not something that is measured or specified as a percentage.
No, actually it is. The most commonly specified impedance of a distribution transformer is Z, which is the percentage of the rated voltage that needs to be appled to the primary to cause the rated current to flow in a shorted secondary.
I thought that was just used for calculating circulating currents for things like fault-condition calculations, etc, like if you have a 10% 120v transformer, 12v would cause full rated current with a shorted secondary....
...but I'm not a power systems engineer, so I'll let those more knowledgeable in the field chime in here.
you can have high efficiency and still have voltage droop. That's because of the reactive impedance. i.e. the leakage inductance in a transformer plus the transmission system.
It is commonly specified in terms of percentage. That is the per unit system that power engineers use. You calculate the full load impedance based on the maximum voltage and current and V/I is the base impedance. Then the percent source impedance is the ratio of the base.
......none of the screenshots posted thus far are as bad as some I've seen.......
Tautech, I was hoping to see some of these waveforms you mention.
......none of the screenshots posted thus far are as bad as some I've seen.......
Tautech, I was hoping to see some of these waveforms you mention.Sorry Joe I never captured them as it was a few years back. This topic has been discussed here before and I can't even be bothered to try to find the threads.
While some members here can't/won't/don't accept that distorted mains waveforms are a fact of life yet others have proved they are amuses me when the explanations for such seen behaviour is quite simple.
Hell even Simon gets it (no offense) when non-sinusoidal current loads can affect sinusoidal voltages from a NON ZERO impedance supply.
As for providing screenshots of mains, there are plenty here already that clearly show what to expect so despite that I've worked a lot with mains over the years I have NO wish to work with it more than is absolutely necessary and recommend those without sufficient experience don't either.
I have strong views about this if only for the safety of others and reported this thread in its infancy for fear that those attempting to measure/view mains waveforms are exposing themselves to unnecessary risk.
......none of the screenshots posted thus far are as bad as some I've seen.......
Tautech, I was hoping to see some of these waveforms you mention.Sorry Joe I never captured them as it was a few years back. This topic has been discussed here before and I can't even be bothered to try to find the threads.
While some members here can't/won't/don't accept that distorted mains waveforms are a fact of life yet others have proved they are amuses me when the explanations for such seen behaviour is quite simple.
Hell even Simon gets it (no offense) when non-sinusoidal current loads can affect sinusoidal voltages from a NON ZERO impedance supply.
As for providing screenshots of mains, there are plenty here already that clearly show what to expect so despite that I've worked a lot with mains over the years I have NO wish to work with it more than is absolutely necessary and recommend those without sufficient experience don't either.
I have strong views about this if only for the safety of others and reported this thread in its infancy for fear that those attempting to measure/view mains waveforms are exposing themselves to unnecessary risk.
That's too bad, I would have liked to have seen them as it sounded as though you had seen some abnormal conditions, compared with the typical I see shown here. These few I presented caused problems and I would say they are not what I would consider normal. Certainly, not anything I would expect in a home. Still, it's a good idea to have some understanding of what can happen on the mains.
One day I hope to find someone that understands the cause of that one oddball.
Joe, which ones are you referring to? And which one is the oddball? I see three jpg's named "fun", and you talk about laying all three phases on top of each other, but I'm not sure I understand.
IMO, the second one is very likely an 8-cycle fault on a remote circuit, which is pretty typical for high speed relay clearing on a power system. So you're just catching the voltage dip due to a remote fault. This kind of trace is extremely common, and happens every time you get a ground fault on a power system line (eg, tree branch gets into the line, etc.). I assume this was captured from an automatic disturbance recording device, and you weren't incredibly lucky to happen to capture an electrical fault when your scope was connected.
I assume the first one was due to some sort of inverter failure (all that sawtooth yumminess...), but without knowing the system configuration and what you're measuring it's tough to guess. And IMO, since those inverter systems are generally proprietary designs, it's tough to figure out exactly what's going on.
The last one needs some more background on what the system configuration was and what you're measuring. I agree it's very strange. If it was connected to the utility, it seems strange to have so much distortion. Lots of harmonics like that makes me think there's some iron-core transformer overvoltage causing saturation, but that would more likely cause flat-topped voltage waveform. Was it an ungrounded system? Were there inverters or other industrial equipment connected? Was this running isolated from the utility, served by a diesel or something?
By the way, never underestimate the likelihood that what you're measuring may not be what's actually on the system As you know, there's always the possibility that the measurement system has a problem. Also, I've found that the more strange an event is, the more likely it's caused by multiple issues at the same time, not just one. Which makes it even tougher to diagnose.
And I assume these aren't individual traces of three phases of a 3 phase system?
We seem to have rather wandered off the original question - what is your ordinary, everyday, normal operation mains waveform like? Mine seems to be very consistent. I've used a 900W jug kettle as a resistive load, and measured the waveform of the current drawn by it. It still looks the same shape to me. The slopey bits aren't even remotely sinusoidal!
We seem to have rather wandered off the original question - what is your ordinary, everyday, normal operation mains waveform like? Mine seems to be very consistent. I've used a 900W jug kettle as a resistive load, and measured the waveform of the current drawn by it. It still looks the same shape to me. The slopey bits aren't even remotely sinusoidal!
Why are you measuring current?
Joe,
I'm not sure what you mean by a load balancing system. Do you mean balancing load between the 3 phases, or circuit balancing, or something else? I'm not familiar with a load balancing system.
Usually when imbalance between the 3 phases is detected (by too much residual current, ie, sum of the phase currents), someone has to go out and manually shift loads by physically disconnecting single phase transformers and moving them to another phase.
Joe,
I'm not sure what you mean by a load balancing system. Do you mean balancing load between the 3 phases, or circuit balancing, or something else? I'm not familiar with a load balancing system.
Usually when imbalance between the 3 phases is detected (by too much residual current, ie, sum of the phase currents), someone has to go out and manually shift loads by physically disconnecting single phase transformers and moving them to another phase.
https://www.utilityproducts.com/test-measurement/article/16002495/saving-energy-through-load-balancing-and-load-scheduling
Products and papers on automatic systems:
https://3dfs.com/technology/loadbalancing
https://nanopdf.com/download/smart-electric-grids-three-phase-automatic-load-balancing_pdf
https://www.matec-conferences.org/articles/matecconf/pdf/2018/32/matecconf_smima2018_02040.pdf
https://www.hindawi.com/journals/acisc/2016/6928080/
Again, to be clear, I never found the cause of this particular problem.
Joe,
I'm not sure what you mean by a load balancing system. Do you mean balancing load between the 3 phases, or circuit balancing, or something else? I'm not familiar with a load balancing system.
Usually when imbalance between the 3 phases is detected (by too much residual current, ie, sum of the phase currents), someone has to go out and manually shift loads by physically disconnecting single phase transformers and moving them to another phase.
https://www.utilityproducts.com/test-measurement/article/16002495/saving-energy-through-load-balancing-and-load-scheduling
Products and papers on automatic systems:
https://3dfs.com/technology/loadbalancing
https://nanopdf.com/download/smart-electric-grids-three-phase-automatic-load-balancing_pdf
https://www.matec-conferences.org/articles/matecconf/pdf/2018/32/matecconf_smima2018_02040.pdf
https://www.hindawi.com/journals/acisc/2016/6928080/
Again, to be clear, I never found the cause of this particular problem.
Ahhh, okay, thanks. So I guess some large industrial customers install stuff like static var compensators (SVC's) to adjust power factor and KVA loading in realtime. Utilities use big versions of SVC's for VAR/voltage control, but I guess something along the lines of what you're talking about are limited to large industrials or maybe small smart grids.
For the most part, utilities balance loads by sending a crew out
This is my at-home mains, L1-L2, L1-L3 and L2-L3, respectively.
Snip ...
This is my at-home mains, L1-L2, L1-L3 and L2-L3, respectively.
Snip ...
I am so jealous, I wish I had three-phase in my house.
I am also homesick when I see 50Hz.
Regards,
Jay_Diddy_B