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Ropetangler
23rd Nov 2017, 09:39 PM
Forum members may be interested to know that not all inverter drives being marketed here on ebay are suitable for use in Australia according to the vendors. I am looking for a VFD for the local Mens Shed, and cheap is a desirable attribute. Almost all single phase VFDs have a 220 volt nominal input, and as the mains can sometimes be north of 250 volts in this country, I thought that I should just make sure that the vendor was happy to guarantee the unit if used under those conditions. the string of messages is shown below.
I know that most people have had no problems operating on voltages somewhat higher than the 220 volts most list as the input voltage, and I am curious to see if many have had any problems as a result.
Rob.





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Dear prues-rob,
Thanks for your letter,
We are so sorry to say that the item is not suitable for use in Australia,Hope you can understand.
Best wishes.








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Your previous message




Just a follow up to remind you as you requested. Any word yet on the warranty of these units if used on the standard mains supply in Australia of a nominal 240 Volts, and not the indicated input requirement of this inverter of 220 volts.
Regards,
Rob.

















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Dear prues-rob,
Thanks for your letter,
I need to check it with the supplier,i will tell you when i get reply,OK?
If we forget to write to you in 2 days,can you please kindly write to us to remind us ?Thanks for your understanding.
Best wishes.














Your previous message




in your listing this item is described as being suitable for 220v input. The trouble is that in Australia the mains voltage is a nominal 240v, and can rise to over 250 volts.
My question is will your inverter give reliable service if used on the national electrical power grid?
What guarantee do you give with this inverter when used on the national power grid?
Thank you and best wishes,
Rob.





























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simonl
23rd Nov 2017, 09:51 PM
TBH I would have no idea of what our supply voltages do in terms of fluctuations.

Call me simple but i just flick a switch and expect stuff to work!

I run 3 Hy VFDs and had no issues. BTW i assume you mean 250V rms as in actual fact 240v actually gets to about 339v p-p anyway.

Cheers

Simon

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snapatap
23rd Nov 2017, 10:03 PM
We changed from 240V to 230V mains a few years ago to get in line with international standards. The Maximum supply voltage you should get is 253V.

Neil317
23rd Nov 2017, 10:07 PM
I think Victorian and Tas nominal voltage is 230, not 240. You are 10v closer to being ok!
Neil

Theberylbloke
23rd Nov 2017, 10:18 PM
Hi Simon,

Australia had a nominal 240, plus or minus 6%, spec for voltage. That meant 226 volts to 254 volts. I think it is now 230 volt with a wider swing to the upside ( I think 14% ?) and still 6% down. The authorities I have worked for have various sets of rules about how long the volts can be outside the limits before they do anything about it. Anything above 254 volts gets looked at pretty quickly these days as Solar systems start to fall off line at 255-256 volts.

Queensland has done some trials on the 230volt nominal system and are going to move to this "shortly" and slowly as it's quite a big job, both in the field and for engineering staff doing the calculations. I don't know what other states have decided on.

Actual voltage fluctuations can have a huge range of causes, way too many to attempt a comprehensive list of here.

The only way to be really sure of what your volts are doing is plug in a volt meter and check it from time to time.

I tend to think it's unlikely that plugging in a 220 volt rated VFD to 240 volts will cause it to fail immediately. You would have to imagine the designers would allow for components that would survive some overvoltage. It may shorten it's life though.

Still if they are not going to warranty it, i'd stay clear.

Cheers

The Beryl Bloke

jack620
23rd Nov 2017, 10:26 PM
Here's the voltage trace of one of my phases from a couple of days ago. Until recently we were regularly exceeding 256V, causing my solar inverter to reduce its output. United Energy came out and dropped two taps on the street transformer, which they told me is about 7V. Note the average is well above 220V.

jhovel
23rd Nov 2017, 10:55 PM
As far as I know, there are no longer any countries in the world running on nominal 220V. Europe went up to 230V a couple of decades ago, the USA went to 115 (and therefore 230V across their two actives). The only continent generally still on 220V is Africa. There are a few small countries still on 240 and a few odd places on 220V.....
I doubt very much that any mass produced equipment is limited to 220V for reliable running.... Almost all VFDs I've seen are rated 200 to 250V when you look at the manuals.

BobL
23rd Nov 2017, 11:32 PM
I know that most people have had no problems operating on voltages somewhat higher than the 220 volts most list as the input voltage, and I am curious to see if many have had any problems as a result.

I have VI meter on my breaker box and on several of my machines so I can watch what's going on.
Usually mains V sits between 238 and 242V but I have also seen it as high as 250 and as low as 228V.

Since 2011 I have used 12 different 220V rated VFDs in my shed and currently have 7 connected to machinery. I managed to blow the caps on one but that had nothing to do with the V supply.

The major issues will be with the ratings on Caps and components. A better quality VFD will use better (higher V rated) components so this will cover most of the higher V rated.

For the Mens Shed at which I am a member I purchased a 3P-3P Powtran VFD direct from the manufacturer and they only cost about the same as the eBay cheapies but they are far superior in terms of quality. I have since bought two of these for myself.

I discuss these in the WWF thread VFD install summaries (http://www.woodworkforums.com/f271/vfd-install-summaries-213878)
The main advantage with them is that they are all true Vector drive VFDs.
They also come with braking circuitry built in for an extra US$5.

There are several different model ranges available from the compact size budget level 160s to the pro level 9000 series.

Here is a comparison of a 160 budget level 1.5 kW Powtran with a HY 1.5 kW VFD showing how compact the PT VFD is
http://www.woodworkforums.com/attachment.php?attachmentid=422437&d=1508205423


Here is a comparison of a 2.2kW Powtran PI9000 (LHS) with a 3kW HY on the right.
Notice how much "chunkier" the Powtran is. They also use bigger heat sinks, a bigger fan etc.
http://www.woodworkforums.com/attachment.php?attachmentid=412381&d=1494839507

The twin line (versus single line) display and the speed sensitive knob on the front of the powtran makes it much easier to set frequencies manual and make program in much easier. The PT also has memories built into the control panel so you can store everything and even move the control panel around to other VFDs.

The PTs cost a bit more but they have so many advantages that make the price difference over the cheapies meaningless.

Ropetangler
24th Nov 2017, 07:59 AM
Thanks gents for all your contributions. I am pretty sure that the VFD which was the subject of my enquiry would have been OK but it seems that either the wholesaler or manufacturer wasn't prepared to risk it, so I don't think that I will either.
Simon you are correct in that I was referring to RMS voltages, as that is what the voltage inputs and outputs of VFDs would be referenced to.
The gradual lowering of mains voltages has been on the agenda for a long time now, but every time I ever measured the mains voltage here at home, it was always around the 240 Volt mark as measured on my trusty Digitech OM1539 digital meter, a $30 - $40 meter not calibrated since manufacture (if then). I took another measurement last night at about 11.00pm and again this morning, and both times the reading was 236 volts to the nearest volt. Maybe the voltage is being lowered, IIRC it was usually a volt or two higher than the nominal 240volts and now it is a few volts lower, but it is still very close to the old 240 volt standard, at least as best as I can measure it. It seems to me that the power authorities are playing with words and not doing too much to change anything for the better, if as The Beryl Bloke says that they are lowering the nominal voltage to 230, but allowing a higher up-side than previously. It ends up being much the same as we have had previously, except that the voltage swings will be much higher while still staying in spec. 216-262V new spec, versus 226-254 V old spec.
BobL as usual a very comprehensive summary of features to look out for, thank you, I will see what I can find in a Powtran VFD offering.

.RC.
24th Nov 2017, 09:54 AM
Here's the voltage trace of one of my phases from a couple of days ago. Until recently we were regularly exceeding 256V, causing my solar inverter to reduce its output. United Energy came out and dropped two taps on the street transformer, which they told me is about 7V. Note the average is well above 220V.

I have read the rooftop solar phenomenon causes mains electricity voltage to rise causing headaches for the electricity suppliers. It is one of the reason electricity prices have risen (the network operators have to spend more on the network to now cater for millions of small scale unreliable generators). It really should never have been allowed.

Our electricity voltage now runs at 250V nearly all the time, due to installation of a boost transformer on our main line to cater for a large rock crushing plant further along the line. They were apparently suffering severe voltage drop when their crushers jammed and the motors started drawing 1000+ amps.

jack620
24th Nov 2017, 10:02 AM
I have read the rooftop solar phenomenon causes mains electricity voltage to rise causing headaches for the electricity suppliers.

True. When the sun comes out the grid voltage rises. That's why the AS was changed recently to require inverters to throttle back to keep their output below 256V.


It is one of the reason electricity prices have risen (the network operators have to spend more on the network to now cater for millions of small scale unreliable generators).

Possibly true. But they are going to have to upgrade the network to deal with renewables eventually. Might as well be now.


It really should never have been allowed.

What shouldn't have been allowed? Solar panels on roofs? :?

.RC.
24th Nov 2017, 12:04 PM
Possibly true. But they are going to have to upgrade the network to deal with renewables eventually. Might as well be now.

Maybe, eventually nuclear will be the only option though, if people want a reliable power source. But there are too many well off silly people around yet for that option to be viable.




What shouldn't have been allowed? Solar panels on roofs? :?

Small scale intermittent suppliers injecting surplus electricity back into the grid.

jack620
24th Nov 2017, 12:36 PM
Gotta love this forum. A thread about VFD voltages generates a post about nuclear power!


But there are too many well off silly people around yet for that option to be viable.

I may be well-off, but I ain't silly. My solar panels will pay for themselves in about 7 years. After that I'm making money. Right now my pool pumps are running for free. Later my air-con will be running for free.

jhovel
24th Nov 2017, 01:11 PM
Hi R.C.
you may get your wish of no "unreliable" generators on the grid one day soon. As battery prices go down and cycle numbers go up, more and more people are likely to stop putting power back into the grid and store it themselves.
As far as being allowed, the electricity generators had no hope in hell to supply all the power required without roof top PV systems a few years ago. THere hadn'r been any new large power stations built for decades and the population had almost doubled since then...

I'm surprised your provider hasn't adjusted your property transformer or installed one to reduce your property voltage - given that they can be held resposible for damage caused by overvoltage (if not by you then by your insurance)...

Also: @Chris: the voltage seems to go up on your graph around 5 hrs AFTER the sun comes up. I really see no correlation in your graph to sunshine. I see high voltage at 3am when there is lo demand and high voltage at 11am when industry is going full power.... Voltage variation is a representation of LOAD (and therefore losses in transmission cables).
What shows supply variations is a bit more subtle and complicated: the electricity providers track FREQUENCY to do that. Grid frequency varies by fractions of Hertz as suppliers come on line and drop out again - including solar generators. That is the MUCH more complicated parameter to manage and control. However, the challenge is exactly the same for gas-fired, coal fired, hydro or solar power generation. Coal fired generators are the MOST difficult to manage in that context, because of enormous inertia.

Lastly, most solar power generated doesn't travel far down the grid - the available current to the grid gets used up LONG before it gets to high voltage transmission lines. Your next door neighbor or the nearest commercial user will use up whatever you might share with the grid.
I'd actually be interested in seeing a current flow map of local and long distance grid transmission. Be interesting to actully visualise the effects of sunshine on the grid....

.RC.
24th Nov 2017, 02:01 PM
Gotta love this forum. A thread about VFD voltages generates a post about nuclear power!

But that is how normal discussion between friends goes.




I may be well-off, but I ain't silly. My solar panels will pay for themselves in about 7 years. After that I'm making money. Right now my pool pumps are running for free. Later my air-con will be running for free.

The sillybit was not referring to you, but the ones who think their electricity use is only what their bill is, totally disregarding how much electricity such entities like hospitals and high rise office buildings and rock crushing plants and so on use. Some people seem to be of the belief their electricity use stops at their property boundary. I have always thought we need to build a hospital that solely runs on renewable energy sources, and the true believers can go there when they are ill. I can remember growing up and our total electricity supply was a 2kva Davey alternator powered by a 4hp YB engine (Both items Australian made)

I love being able to flick a switch whenever I can and the light goes on. My parents never saw mains power until they were in their thirties. Before that it was all intermittent diesel generators and kerosene fridges. (Intermittent as you could run the generator all the time due to cost) Summer time was mosquito nets and restless nights. No fans, no air conditioners.

I do not care how electricity is generated so long as it is affordable for everyone and reliable and preferably creates new industries and research rather then just buy something in from overseas and all we do is mix some cement to install it.


Hi R.C.
you may get your wish of no "unreliable" generators on the grid one day soon. As battery prices go down and cycle numbers go up, more and more people are likely to stop putting power back into the grid and store it themselves.
As far as being allowed, the electricity generators had no hope in hell to supply all the power required without roof top PV systems a few years ago. THere hadn'r been any new large power stations built for decades and the population had almost doubled since then...



I think they are a long way off yet. Another thing that is odd is that while some people go on about the emissions cost, the social and real environmental cost is never included by them. You only have to google about the working conditions and environmental destruction caused by mining rare earth elements and other things needed by the renewable market and suddenly it is not such a great thing.

Rare Earth elements are not rare, but the processing of them and making them still to be easily affordable can only be done when it does not matter if your workers are poisoned or killed.

There used to be a solar cell manufacturing plant in Sydney. Where is it now?

jack620
24th Nov 2017, 02:58 PM
I really see no correlation in your graph to sunshine.

Good observation Joe. However, that isn't the phase my inverter is connected to. I posted that one because it had a large variation in max and min voltage to demonstrate how wildly voltage fluctuates. I've attached another trace with inverter power vs voltage for the connected phase. You can see a definite drop in V when cloud covers the sun and an increase in V when the sun comes out again. But there are also voltage swings that are unrelated to solar output.

I get an email every time my inverter has to throttle back due to over-voltage. That doesn't happen very often these days, but when it does it's always when the inverter is pumping out a lot of power.

jack620
24th Nov 2017, 03:05 PM
The sillybit was not referring to you,

Fair enough.


There used to be a solar cell manufacturing plant in Sydney. Where is it now?

China or South Korea I guess. Realistically though, we were never going to be able to produce solar panels that were affordable. I believe the Germans are now out of the game too. Even with the government rebate my South Korean panels were expensive.

BobL
24th Nov 2017, 03:13 PM
You only have to google about the working conditions and environmental destruction caused by mining rare earth elements and other things needed by the renewable market and suddenly it is not such a great thing. Rare Earth elements are not rare, but the processing of them and making them still to be easily affordable can only be done when it does not matter if your workers are poisoned or killed.

REE are not used in Solar panels


There is a very wide range of metals (http://www.futuresmag.com/tag/metals)used in solar panels and many are used in minute quantities. These are, in alphabetical order: Arsenic (used in semi-conductor chips), Aluminum, Boron minerals (used in semi-conductor chips), Cadmium (used in certain types of cells), copper (used in wiring and certain types of cells), Gallium, Indium (used in cells), Iron ore (steel), Molybdenum (used in photovoltaic cells), Phosphorous, Selenium, Silica, Silver, Tellurium, and Titanium.

Interestingly REE are used in petroleum distillation.

while a crucial process in the conversion of petroleum into gasoline uses lanthanum and cerium.

The vast majority of REE use is as a catalyst for petrochemical and other processes
The amount of REE used to crack petrochemicals into petrol for the lifetime of a vehicle is about the same as the amount of REE needed in the batteries and magnets needed by electric vehicles.
371253


The batteries of most hybrid gas-electric vehicles use magnets that include quantities of dysprosium and neodymium.
But the major elements in battery use are of course Li and Pb all of which including the REE are highly recyclable.

Uses of REE see Rare earths: uses, applications-Metalpedia (http://metalpedia.asianmetal.com/metal/rare_earth/application.shtml)

Ag and Te (3 times rarer than gold) are expected to be the main metal cost limitations in PV production - buy your tellurium mining stocks here. Fortunately the excess Ag from the no-longer used Ag in photo film has found a new home and apparently it won't be long before the demand for Ag in PV exceeds the peak Ag use in the era of film based photos.

BTW I don't have any solar panels and no plans to buy any either.

jhovel
24th Nov 2017, 03:21 PM
That's a really interesting graph, Chris. I had not expected that.
Since you ar obviously interested in this, are you able to overlay all three phases - and maybe your inverter output as well? I'd be really curious if cloud cover was reflected on all three phases (mainly). The inverter trace isn't voltage - right? - what units is that showing?

jack620
24th Nov 2017, 05:12 PM
Since you ar obviously interested in this, are you able to overlay all three phases - and maybe your inverter output as well?

Sure Joe. Here's yesterday's traces. My inverter is connected to the phase shown in yellow. I don't know which phases my neighbours are connected to. The inverter trace is Watts. I managed to cut that off in my previous screenshot. Volts seem to follow Watts when there are abrupt changes in inverter output. Less (no?) correlation when inverter output changes gradually.

Theberylbloke
24th Nov 2017, 08:19 PM
Hi Jack620,

The longer term correlation between your inverter's output and the voltage is masked by the power network's operation. The network operators employ automatic voltage control that continuously monitor the network and adjust the voltage to with a 2.5% band. They normally operate when the voltage gets outside the band for 60 to 90 seconds. It can also be masked by how much power you use on the premise.

The other thing you know is that most panels produce less power as they get hotter. A cloud passing overhead gives them a chance to cool down. When the sun comes out, output climbs and then falls as the panels heat up.

I have seen voltage swings from 240 to 228 due to an aluminium smelter coming online some 200km away. The aluminium smelter was connected to the state 132,000 volt system and was driving the entire states grid up and down as it went on and offline. It was all sorts of funny/sad attempting to explain to a small shop owner why he had a problem. Took a bit to convince skeptical bosses, at least at first. That was a long time ago and I doubt that still happens.

Solar generation does travel into the high voltage system and can do for very long distances.

The electricity networks were designed and built when the idea of customers generating power back into the grid would have been considered lunacy. Changing the designs and operation of the systems is a slow process. A lot of money invested in the infrastructure, a lot of people adversely affected if you make sudden poor planning decisions.

What will drive people off the grid is poor politically motivated decisions abouth the cost of power etc. Batteries get cheaper by the day. Aggragate roof top PV is the largest generator on about 115,000 buildings or about 1 in 4 houses. If prices get too high people will go off grid. Take away the 44 cent infeed tarriff inspires all those people to go off the grid. This is a minefield that no angel would enter.

Renewables are not as variable, en masse, as many suppose. Sure if it's cloudy at my place solar output drops, unlikley to be cloudy at both your place and my place at the same time if we live 1000km apart, thus the greater the number of renewable generators the less the variabilty. Sure when the sun goes down PV stops. Batteries will solve that. Also because of the geographic spread network reliability improves.

I experienced a powerpoint presentation today ( I barely survived the 5.5 hours of it and have the mental scars to prove it) Apparently the network specs are 230Volts +- 10%

Cheers

The Beryl Bloke

simonl
26th Nov 2017, 08:51 AM
Hi Beryl,

Can you explain how peoples rooftop PV power gets injected back into the high voltage supply?

If it gets injected into the grid in peoples homes at roughly 230v then where and how does it get up converted to HV again?

If its already mixed in with 230v power that has been down converted from the HV supply then why would you invert it back to HV?

I dont understand.

Simon

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Theberylbloke
27th Nov 2017, 09:36 PM
Hi Beryl,

I dont understand.

Simon

Sent from my SM-G900I using Tapatalk

Hi Simon,

The previous normal power flow was that it was generated in large power stations and then stepped up to 132,000 volt (or 275,000 volt) transmission lines. Those lines are the backbone of the network. They run to what is referred to as a "bulk supply" substation where the 132,000 volts is stepped down to "Sub-transmission" voltages generally 33,000 or 66,000 volts. The voltages fed into the sub-transmission lines are automatically regulated. Those sub-transmission lines then feed local zone substations where the 66,000 volts is again reduced to 11,000 (or possibly 22,000) volts, this voltage is also automatically regulated. So the voltage here is essentially fixed.

The 11,000 volt line feeds the distribution transformer near your house that steps the voltage down from 11,000 to 415/240 volts. That step down is not automatically regulated and is fixed (for arguments sake). Transformers are very efficient at converting power from one voltage level to another. However they really don't care in which direction they are converting it, they step up as well as they step down, no questions asked.

Voltage drop in a conductor is calculated as the current through the conductor (in amps) multiplied by the resistance of the conductor (in ohms) Thus your electric hot water system might draw 15 amps and the resistance of the conductors between your distribution transformer and the hotwater system might be 0.4 ohms thus the voltage drop at the hot water system is 6 volts.

Lets assume you are the only person connected to your local distribution transformer. Your solar system is generating 15 amps back into the grid. That reverses the process and causes the voltage to rise at the inverter by 6 volts. As the power can't be used locally, your inverter will continue to force current into the mains raising the voltage a little more and in doing so back energises the local distribution transformer (which doesn't care) and raises the voltage on the 11,000 volt distribution line.

For sure a single inverter won't do much. They are set to trip off at around 256 volts. En masse? that's quite different. I am aware of situations where long rural 11,000 volt feeders have been forced up to 265 volts at transformer terminals. Sometimes, automatic voltage regulation, is installed in long lines and I have seen it stop working when the power flows in the "wrong" direction. I have not seen, nor know of, any situations where power flow through a 66,000/11,000 volt Zone substation has reversed. I doubt that situation could arise under current restrictions on solar, however, I am curious about this now and will chat to my friendly local engineer. I suspect this situation might not end well !

Issues of inverters dropping off line because the volts get too high are due to too much resistance in the lines between the inverter and the distribution transformer. Usually this means the sizes of wire is too small or the distances too great. Thus the best advice I can offer anyone thinking of putting on Solar is to have their proposed installer do what is called a "loop impedance" test (this tells you the resistance of the circuit) at the proposed location of the inverter and have them calculate the voltage rise at full inverter output. If your installer hestitates, find another installer. This can save everyone a lot of angst later.

Sorry for the long post. If you need clarification on anything, more than happy to provide it. Also apologies if I have made it soo simple or too complicated

Cheers

TheBeryl Bloke

simonl
28th Nov 2017, 08:32 AM
Thanks for the reply Beryl. Learnt some more stuff!

Simon

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.RC.
28th Nov 2017, 04:07 PM
Another issue is nasty harmonics being generated. I have read power these days is dirtier then in times past. Amateur radio people really notice it.

eskimo
29th Nov 2017, 06:40 PM
what ??? !!!! if the name tag says it will work on 220 then I reckon it will work on 240. does for me...:D

eskimo
29th Nov 2017, 06:41 PM
Another issue is nasty harmonics being generated. I have read power these days is dirtier then in times past. Amateur radio people really notice it.

and they create the most interference...but hey I like them

Ropetangler
30th Nov 2017, 01:50 PM
what ??? !!!! if the name tag says it will work on 220 then I reckon it will work on 240. does for me...:D
I agree Eskimo, but if the seller has doubts, I don't think that I'll take the chance, especially when BobL points out a superior alternative, for not much extra!:) I was quite surprised to get the reply from the seller that I did, when all I was really after was for them to put in writing that the device was suitable for use on Australian mains supplies. I do feel a little uncomfortable when manufacturers quote an input voltage requirement of say 220 volts plus or minus 10%, which leaves virtually no headroom if the local supply is 240 Volts. In the old days, I have seen voltages above 250V, but in the last couple of days it was around 232 to 234 volts. Today it is 239.7 volts according to my fairly cheap and never calibrated Digitech QM1539 multimeter which cost IIRC about $40 about 10 years ago. The talk of our voltage being harmonised with the rest of the world, and being lowered to 230V, isn't ringing true to me, it seems more a case of them loosening the specification, to make life easier for the generators and power distributors, and make it harder for consumers to claim damages against them for electrical events caused by over or under voltage electric supply.:rolleyes:
Rob.

BobL
30th Nov 2017, 02:34 PM
If you want to buy a VFD that claims to be rated for 240V then try these Folinn VFDs from an Australian Supplier.

A 2HP unit costs $235 and is a full vector drive - being an Aus supplier is a plus.
https://www.ebay.com.au/itm/1-5kw-2HP-7A-240V-AC-single-phase-variable-frequency-drive-inverter-VSD-VFD-/172761255022
I don't believe they are quite as good as the Powtran 9130 series but still a respectable unit.

The seller makes a big deal of saying they are rated and warranted for 240V +/- 15%

If you go to the Folinn website you'll see these VFDs are rated at 220 +/- 15% and I doubt the factory would change anything for a small australian supplier.
My guess is they already use reasonably well rated components and just change the sticker to reflect what the Aus buyer wants. This is fairly common from chinese suppliers.


.

Theberylbloke
30th Nov 2017, 05:57 PM
Another issue is nasty harmonics being generated. I have read power these days is dirtier then in times past. Amateur radio people really notice it.

Well it's not just the PV inverters. Everything has a non-linear switchmode power supply because they are cheaper. When was the last time anyone here bought an item with a step down\up transformer & full wave rectifier power supply? early 80's probably. A VFD is essentially a non-linear switchmode power supply as I understand it (see, still on topic:no:)

I'm told the fun really starts when you have a big office full of PCs with the load nicely balanced across all three phases. Then because they are all switchmode non-linear power supplies you get all of the return curent in the neutral conductor i.e. total load of all three phases. Neutral connections burn out or the insulation melts off the neutral just before the cables burn apart. Easy fix, just replace the neutral conductor with one rated for three times the phase load.

I have seen the harmonics on an 11,000 volt feeder with heavy solar loads. There seemed to be lots of harmonic voltages present. Interestingly the actual harmonic currents were quite low and did not seem to bear much relationship to the voltages. Highest harmonics were the third and sixth? I have no idea as to the accuracy of the measuring equipment so this is purely anecdotal.

Non the less I am at a bit of a loss as to how powerline frequency harmonics interfere with ham radio operating at much higher frequencies. Not saying it doesn't happen just personally ignorant.

Cheers

The Beryl Bloke

simonl
7th Dec 2017, 07:17 AM
I always thought that if the 3 phases are balanced, you end up with next to zero current flowing through the neutral.

Simon

Mike4
6th Jan 2018, 10:44 AM
I am still getting a diesel 3 phase gensetas the main standby or full supply as the electrical system is still pretty unreliable ,I use power on a 24/7 basis .
Its ok for the 9-5 office dwellers and the like to have solar and batteries ,but many of the solar setups swicth off if the mains drops out during a storm , that is not what I specified when the fabulous roof decoration was purchased , I found out the hard way when a transformer died and let its smoke out .
6-8 hours without any power .

Solar may suit some but currently its not giving me any pleasure.

Michael

BaronJ
6th Jan 2018, 05:10 PM
I always thought that if the 3 phases are balanced, you end up with next to zero current flowing through the neutral.

Simon

That is correct for a balanced load such as a 3 phase "Y" wired motor !

Though you might be surprised how many times you get a neutral burnout, at least here in the UK, where estates of houses have one side of the street wired to one phase and the other side wired to another and the third one wired somewhere else. Simply because all the return current has to flow through the neutral. All the major power failures where I live have been due to this cause ! Except for the one time the local sub station transformer went up in flames, and that was blamed on an overloaded neutral.

These are "Y" connected systems. In a "Delta" connected system the current flows between the phases, the neutral may not even be present.

Theberylbloke
7th Jan 2018, 11:03 PM
I always thought that if the 3 phases are balanced, you end up with next to zero current flowing through the neutral.

Simon


Not sure if this is addressed to me, I'll answer it anyway.

In a low voltage delta system the phase currents flow to and from each phase without reference to a neutral. A 3 phase delta wound motor would be a good example of this. Notice that at any given time in the A.C. cycle the curernts flowing are proportional to the applied voltage i.e. limited only by the impedance of each coil. This load is said to be linear

In a star connected system the currents flow between the active to the neutral via the load. The current may not return to it's origin via the neutral. The easy example is a street of houses with three phase and neutral supply, with each house having only single phase power to it. House number one is on A phase, House number two is on B phase & house number 3 is on C phase. When A phase of the A.C. cycle is at it's positive peak, B and C phase will be below zero volts. The current that house one draws goes back to the neutral. However as the other two phases are below zero that same current will split and return to it's source via houses two and three. If all three houses are drawing the same current from the mains, none of the current will travel back in the neutral to it's origin. There will be current flow in the neutral between houses. If house two stops drawing curent then part of the current from house one goes through house three and back to it's source and the remainder of the current travels through the neutral to the source. Note that we are talking about linear loads.

Imagine a street of houses where there are 7 houses on A phase, 9 houses on B phase and 5 houses on C phase. The load on the individual phases is 26 amps, 41 amps & 8 amps. The neutral carries the out of balance current, in this case 35 amps. We know that conductors have resistance and that it takes a certian voltage to cause a given curent to flow through a conductor. In this example the 35 amps in the neutral requires say 6 volts along it's length for this current to flow. Thus the end of the street furthest from the transformer will have the neutral 6 volts above earth potential, enough to cause shocks and tingles to those living in that area.

Examine a modern computer switched mode power supply. These are not linear loads. During the A.C. cycle they only draw current if they need to and only for as long as they need to, could be milliseconds. They do not care what part of the A.C. cycle they are drawing load from. The load is not proportional to the A.C. waveform. They are non linear loads. Going back to our three houses, if a switched mode power supply turns on in house one the likelyhood that there is a switched mode power supply in houses two or three able to take the current from house one is pretty much nil. Thus all the current from non linear loads pretty much ends up in the neutral. Keep in mind that almost all electronics are switch mode power supplies.

Does this answer your question?

Cheers

The Beryl Bloke

simonl
8th Jan 2018, 08:20 PM
Yes, thank you. A very good explanation.

Simon