US equipment issues (explosions) when used in Australia

I suggest that you contact member MASU directly with this question. From recent comments he has shown a remarkable understanding of the difference between US type domestic appliance connection and Australian appliance connection.

I suspect that it may link back to our "active/neutral/earth" system and the difference to the split power system that is used in the US to achieve 220Volt.

In Australia, Neutral and Earth are linked (hard wired) together at the house distribution point. There is only one "energised" conductor in the three pin 240 Volt sockets that we use.

As you have hinted there seems to be a distinct possibility that somewhere in the system there is a loop of power to ground.

For instance, if you have used a US centre tapped 220V transformaer where by (US) convention the centre is common/neutral and mounted that "neutral" point to the chasis and the Australian lead has its neutral also connected to the chasis, the there will be a 120V potential between those supplies, equals instant schrapnel from the fuse. (Maybe)

Thank you for your comments Just an Engineer. I did want to clarify one thing. These failures are sometimes immediate and sometimes take many months. There is not a wiring issue that immedately puts a 120V difference on the fuse or everyone would fail on initial power up.

I am aware of the different grounding and derivation of 220V schemes. My hypothesis is that there is some issue with ground not always being 220V below the hot side (floating ground) although from what I have read on the web, that sounds unlikely.

Eddie Hunnell

Let's assume this is a new product and you found the problem from the introduction of the product. This would be a design issue. You would do yourself a favor if you first locate a testing standard for your device. I am sure that there are a minimum set of requirements for products in the Australian medical market.

Some organization will be responsible for setting those requirements like surge, leakage, voltage minimums and maximums, static discharge, etc.

I would pick the standards that apply to the next level of equipment if possible and test to those standards. My guess is that the secret lies there and there will be some test that you will fail.

You should also get a copy of the electrical power grid specifications both for commercial power and hospital power as well as specifications for the specific environment the equip is designed to operate in.

I used to work in the medical industry and now work in avionics. However, both industries must answer to a rigorous set of standards and the testing requirements are very well spelled out. If you pass those requirements you have nearly a 100% confidence that the product will perform as designed. That's why they have those requirements so well spelled out when operation is life-critical or safety-critical.

Now, that being said, I should ask if this specific product that fails has always failed in the field in Australia since its introduction or has this product worked for a period of time without failures, but now recently fails for unexplained reasons?

If the answer to that question is the latter, then you need to ask "what changed?" Then go from there. I would urge you to consider hiring a Six Sigma contractor (Black Belt) to track down the process fault. Obviously, if they worked before and they don't now either you have what is called a special cause or an assignable cause and you have something in your process that is running out of control. A Six Sigma expert can not only pin that down and correct it, but give you the statistical tools you need to keep it from ever happening again. That's a bargain.

Normally, I am not a big Six Sigma fan because it is abused so often, but in this case it may be the right medicine for your ills.

That was worth a good answer point Gerard. Hope it works for him too. Ky.

Thank you KY.

Ummm, sorry to correct you, but the standard is officially 240 ±6%, but more like 230 +10 -6

But the standard is being slowly decreased from 240 -> 220 over a period of time to come inline with other countries running 220VAC

So, you can have 225.6 -> 254.4VAC

The MOV devices are generally 275VAC

The power line monitor I have at home on my UPS runs at about 240.4VAC

I agree it would be 240 plus but I would say to test his fuses at 290 to be sure they do not blow because I feel 270 would easily be reached with a surge espically when they switch generators without getting them in sync before engaging.

290 is too high.

275V is the general value of the Surge-suppressors used in equipment here in Oz

If you test to 290, you'll start having more problems, even on locally produced equipment

Hi Gerard ESM Inc.

I liked your answer too. Sometimes we overlook the little things that can make the major difference.

Mark

Thanks Mark.

JD

You have a few good answers already, but I thought I'd throw in my 2 cents for what it's worth.

US power system is 240 volts line to line; 120 volts line to neutral/ground. Australia is 220 volts line to neutral/ground. If you are wired for US 240, you may have to rethink the input power and possibly the wiring of the heating element(s). A schematic may help all of us to get you better answers. However, the suggestion to think US 277 volts is a good one considering US 277 is 277 volts line to neutral/ground (480v line to line).

Thank you all for your input. My issue is I am remote so I dont have any of the equipment in front of me. I have to ask questions to a technician so it is a slow process. I am thinking now that the power module we have in there spec for 240VAC is probably US 240VAC like some of you said and it needs to be higher due to the line to ground reference in Australia.

After talking with the dealer who has seen these in Australia, he has seen them fail (fuse explode) the first time he turned them on and he has seen 4 different units fail in 4 different labs across Australia after many months in the field. So it is not always a day 1 failure.

I also know that there are MOVs across the line. I don't know their spec yet but am wondering if their failure mode could be a short as opposed to an open.

Eddie

The Australian continent is large and mostly arid, and this often means that the neutral-earth link (usually at local substation) may be poor, and a long way away. For this reason a large voltage relative to earth MAY appear on the neutral conductor. In some cases it can reach up to 60V. You will never see this in the coastal cities, where the substation is normally only a stone's throw away and usually the neutral voltage is less than 10V relative to earth. There are stories of nervous cows not wanting to be milked because of a large differential between the milking equipment earth and the local earth potential, earth is just not reliable in some regions.

What to do about it? Maybe the casing needs to be isolated (e.g. triple insulated). It the device hooked to water or gas outlets? This might explain the large current through the earthing.

Hi, Guest!

Good point about the arid continent, the cow milking and hooking to water outlets. They may all be clues to the real problem!

In each case one must take into account the Coriolis effect.

Perhaps the emf rule of thumb is for left-handers only in Australia, and the US equipment, obeying the right-hand rule of thumb, is backing up the current through the transformers and burning them out with a flash!!

Mark

With power lines, there is 4 wires, 1 for each phase and a Neutral (the 5th switch wire is being removed in favour of light self control or remote control by other means)

1 phase and a neutral comes into each house (3-PH if you order it)

and 3-PH into factory establishments, the Neutral from the mains supply is connected to the Earth bonding rail in the distribution box, and a seperate Earth bonding post is nailed into the ground in a suitable location.

So, the Earth point for each establishment is at or close to the incoming termination point.

If your living on a farm or Rural location and have a single wire feed to your house, then a 2nd wire is taken to a grounding point for power feed to the transformer.

could phase differential be the source of your problem. As fluxuations in power occur the magnitude could vary beyond your capacity to handle it. 120 has a smaller range than 240. a capacitor as a part of the fuse might overcome your problem. Maybe it could be a light emitting device as well. At least it sounds better to make the light than explode the fuse.

Just a thought, but those Aussies are pretty friendly and you could probably find somebody willing to send a schematic or 2 from equipment that is manufactured in Australia that requires similar power. You can then compare them and see if there are any obvious inconsistencies.

Hi Eddie

what u have done! in US it is 60Hz mains and in Australia its 50Hz main(British).

even an SMPS will will not be good.

First check for this.

For more help,I'm with u.Even u can also help me.

srikantan.kc

Bangalore-India

srikantan.kc@hcl.in

The problem is simple and obvious. Austrailia is on the bottom of the Earth. When they unpack the device down under, it is upside down. The electrons all run out the top. When it is plugged in the current surge from replenishing the missing electrons causes fuse failure... (Sorry just couldn't resist.)

The problem is simple and obvious. Austrailia is on the bottom of the Earth. When they unpack the device down under, it is upside down. The electrons all run out the top. When it is plugged in the current surge from replenishing the missing electrons causes fuse failure...

TIC

I KNEW IF I WAITED, SOMEONE WOULD COME UP WITH THE FIRST FELICITIOUS ANSWER THAT POPED INTO MY HEAD.

Life is good when you can laugh.

MR. GUY

If you give me a(full time) job working with your co. I can fix your prob...

We have similar electric suppy in India like Australia. Whenever I get any of appliance mfd in U.S I simply buy step down transformer suitable for 240/110 v. For me it works for years.

I agree with you, we do same in Nigeria.

In addition, for the benefit of the original poster, it is important to learn from the reported incident that equipment shipped offshore must comply with the destination country's regulations.

For subsequent manufature/shipment to Australia, I will advise that power supply unit of the equipment be built to 220-240 VAC/50HZ input. Alternatively, build two units; 110VAC/60HZ and 240VAC/50HZ and a switch to toggle between the two (if equipment is for local use or to be shipped to some countries other than Australia alone)

Cheers

ethobil

I must say I am very pleased with the response I have gotten. I have received responses from 4 or 5 continents. Experience like that is very helpful. I will try to address some of the questions.

This product is 20 years old (at least one of the 3 with the same problem - and yes they all use the same power module). It was originally designed to work in the US. I worked for the company 20 years ago when it was designed (as a technician while in college). I just started back with them. So while I know some history, I dont know what happened in between for the non US versions.

I know there were changes made for the non US versions including a different transformer for 240VAC, different heater coils to maintain the same wattage at the different power voltage, and different power modules. However I can not be sure yet that the international versions were tailored to each market. I suspect there are only 2 versions, 1 for 120VAC and one for 220 - 240VAC. Again I have requested wiring diagram, part numbers, etc but dont have them yet.

I do not know how they were shipped. I know they are usually packed well. I do not know what the root cause is (ie did something break or not). There is a power module that receives a typical PC type power cord. It includes a fuse on each of the 2 lines, a double throw switch, and possibly some MOVs before the power goes seperately to the heater coils and transformer that powers the circuit board. The dealer that had the problem replaced the power module and threw it away so I don't have any to look at let alone have someone else look at it. When the fuse blew, it blow a hole in the fuse cover so it was violent (nice current rush). The dealer will send me the next one that blows.

Again I believe everything that sees AC power is not the 120 version and is not wired for 120VAC. But as I mentioned I have not confirme if it is 220V, 240, or higher rated. The solutions by the dealer did not involve rewiring. And I dont know yet if the heater, transformer, etc are rated for 50 Hz or 60Hz although I doubt the frequency rating would cause an immediate explosion of the fuse when powered. I would expect that type of issue to take a while to manifest itself (such as overheating of the transformer). Voltage specs are my first line of investigation.

We have only tested it (at least in house) with US power (so 60 Hz) but as high as 250VAC with no failures.

I like the suggestion of an isolation transformer although am not sure what regulatory requirements I have (ie does the fuse and switch have to be before the isolation transformer - if so I may be back in the same boat). Although remember that this is lab equipment - not anywhere near a patient. The equipment is not portable. It sits on a bench in a histology lab and does not move. But it is not heavy either (15 - 25 US lbs).

I have a bunch of suggestions to talk over with my peer and to do some follow up investgation when I get the part specs and wiring diagrams. Thank you all again.

Eddie Hunnell

And thanks for the feedback! Hopefully you'll see fit to report what you can on the resolution?

Also hopefully the dealer will have nothing further to report...I think you've already made life exciting for enough Ozzie histologists!

Not only worth a GA, but very interesting as well. Many thanks.

Concur with Andy on GA (so voted). So is there any practical way to prevent the situation in your first case, applying random degrees of 0 to peak voltage to a transformer? How would you know where the 0 point was?

Firstly, I do believe that the transformer needs to be of the best quality with regard to insulation and type for the job, secondly, there are chips around that detect and indicate the "Zero" crossing point if needed.

I personally feel that a quality transformer of the correct type is enough to stop the problems.....as there were many years when such Zero crossing chips were not even invented and we got by without!

Also, these chips would have to be on the primary side to do what is desired and there they would be "open" to any large spikes that are on the mains, exposing them unnecessarily I feel......they would be better used on the secondary side to only power up equipment on that side once a stable AC voltage is available......

I still feel that the point that Masu made is still VERY valid for any US built equipment though......and please Masu, do not read the above paragraphs as disagreeing with the problem(s) you described, I am only disagreeing about the possible way to fix them slightly!!!

G'day Andy,

You are absolutely correct in that the transformer should be capable of handling peak voltage power activation without it getting through into the system. Unfortunately the bean counting corner cutting idiots that are all too common now will change a design and install a cheaper transformer that is primarily crap without telling the design engineer.

Many years ago I was working for PR1ME computer when they bought out ComputerVision. In one of the CV systems they had these great ferro-resonant double shielded 2.5 kVA transformers and when they were replaced the transformers some how managed to find their way into my I'll need that one day collection of goodies. I only have one left but they have certainly cleared up some really weird problems over the years.

Over the years I managed to accumulate some real goodies like stepper motors, suction pumps from those big old reel to reel tape drives etcetera. Unfortunately we were forced to move house last year and we no longer have the space to store my collection of

"Don't throw that out I might need it some day collection."

As per Murpherial law, just about everything that went to the tip was needed within a month of the clean out.

PS I did manage to keep one of those transformers and a handful of really great little 12 V stepper motors. I just love stepper motors, engineer em properly and you can replace all the feedback stuff with a simple up down counter.

Using your experience as well as mine, I tend to feel that some underrated transformer could then be part of the failure sequence, putting strain on other underrated components further along the line....

Really, someone like yourself should be asked to take a look at a new power supply and see what needs replacing BEFORE installation, as such explosions can take a lot more kit with it!!!

Sad about the stuff you had to throw out, I had to do the same a few years ago as we deepened and enlarged the cellar and it had nowhere to go!!! I also worked for a couple of computer companies too at one time......I remember when big reel was REALLY BIG!!!

GA. How does the OP solve the problem? Would a capacitor wired to the power leads allow a cushioning effect of the current rush if it occurs near the peak of the wave?

Hi,

you said : "We have tested the product in house using a transformer and ramping the voltage up to 250VAC and left it running for days with no issues", do you mean that you are test in USA.

Can you refresh my memory, if J am wrong, but is it in Australia diferent frequency of electric current in relation to frequency of electric current in US.

Because this you can have some issue with transformer, which is possible to indicate with some failure.

Also J supposes that in all case were you had failure you do not had some other problem on equipment?

I like the ideas already posted where it is suggested that the equipment is wired in it's 110 volt mode, and then plugged into 240 volt supply.

Are the cable colour codes the same??. Are the pin arrangements the same.

There have been a lot of good suggestions, one area of concern I have is whether or not the fuse is properly rated for the application. I am curious why a protection device is not failing in a "safer" maner. I doubt that it is as simple as a wrong fuse but at the very least there may be another underlying issue there.

Do you have access to destroyed units? In some ways to me this almost sounds like an ESD issue where a component is being damaged to some extent by ESD and eventually fails. (i.e. a shorted transistor or similar) This then causes excess current draw and the fuse to open. It would be interesting to see which components are failing in a number of samples and see if there is any coorelation. Good luck!

Shawn

I concur completely on this response. The appropriate course of action would be to inspect one of the failed units as soon as possible post-failure.

I have experienced (many years ago) similar problems with US equipment installed in Europe, also 240 nAC 50Hz. Equipment from several different US sources....

The problems we saw I fixed completely by changing various Diodes, SCRs and Triacs in the mains supply units from 600 (sometimes 800) volt versions to at least 1000 volt versions.

A small spike on the 240 volt mains quickly exceeds 600 volts and can cause such devices to go short circuit. I know that you still do not have a damaged example yet to examine, but I am pretty sure that you will find out that something like I said has happened.

One other point, although we had no further failures, I have spoken with other Engineers about this and the general opinion was that even 1000 volt versions could be still a little underrated......so err on the side of above 1000 volts, not less....if you err at all....

Build all new versions with such components and I feel that all problems will be solved. Also, change the supplier of the fuses and go for a Ceramic body, not glass.....

Best wishes.....

I believe the posters suggesting a step down transformer might be onto something. Not a step down transformer, but an isolation transformer (which a step down transformer would serve as one). It seems that one common thread that keeps coming up is a ground loop/floating ground problem. The way to solve that is to isolate the neutral from the ground. An isolation transformer will accomplish that. That way you can ground the chassis without worrying that you are inducing a ground loop.

The thing to remember here of course is that the equipment does need to be grounded after the transformer for safety (medical equipment).

Didn't the original equipment have a transformer anyway that would have provided isolation?

I thought the fault was on the un-isolated heater circuit (and I don't know how big this is) but the additional weight for yet another transformer might be unacceptable to the end-user especially if the equipment is deemed 'portable'.

That is exactly my point, the heater coil wiring is almost certainly the culprit because it's neutral is NOT isolated from ground.

Well this is a given but you night not know it.

When we had a problem like you having we try and recreate the problem in the lab. Hit it with high volatge and see what it takes the same kind of damage your seeing with the product in the feild. All the lessons learned about the product will come in handy down the road so very much wortht the investment.

avi-tech, frequency could be an issue with aircraft because the frequency is 440hz instead of 60. In this case the difference is only 10 hz, not 380 hz, which is +633% vs -16%. I really think the issue is one of a ground/neutral issue in the heater wiring ahead of the step-down transformer. I've seen floating ground/neutral issues with miswired "hot chassis" SCADA equipment inwhich the neutral and the line were reversed being plugged into properly wired and grounded equipment blow the blades off a NEMA 120V plug (and toast expensive oscilliscopes).

I will like you to also check the frequency . I kwon US is 60Hz but I dont kwon of Australia.

Without a wiring diagram I can't be sure but if those units are switchable between U.S., 120 v.a.c., and Europe, 240 v.a.c., and in Australia you try to operate them the same way, e.g., switch to 240, then your problem is in your wiring which will accommodate Europe but not Australia where 240 is not derived from a system where a center tap, on a coil that has 240 across the full winding, derives what we call neutral, i.e., 120 to either side of the winding, grounded or not.

Obviously what you are getting in Australia is the full 240 across what is basically, if you take away the dual voltage switching, a 120 device. That of course represents what you might call a catastrophic short.

Again, you will need the wiring diagram to see it. I hope you will put that up here when you get it, problem solved or not, because for us folks here in the center-tap States the Australian system is exotic and, if I am right, will show how long use of a particular system makes us blind to others and the cross system complications that might arise.

The simplest way to avoid these problems is to make export equipment with a transformer whose primary matches the power system of the country the gear is going to.

j.

I finally received a wiring diagram which I have posted below (if it posted correcty). I can see its legacy in the US wiring and I assume that 2 of the 3 MOVs are redundant or useless given the "single ended" 240VAC instead of the way it is done in the US. Please provide any other relevant comments as I am not a wiring expert (more a processor, sensor, small signal DC, and software kind of guy). Note that the wries on the right go to heaters (that are spec properly for 240VAC) and a power supply for a computer board. Thank you,

Eddie

hunnel, is there any way you could blow that puppy up a bit? These tired old eyes are crossing trying to read that schematic.

The picture I linked in fills the width of my 17" screen. I am not sure how this blog shrunk it and am not sure how to make it bigger in here. If you give me an email address, I could send the original.

Eddie Hunnell

hunnell@mindspring.com

Has anyone checked the insulation between the heating element and ground? most immersible heating elements are enclosed in a grounded tube. If there is a breakdown of that insulation, you could be shorting to ground in the heating element. This would also explain the variability in timing.

The heaters are flat heaters siliconed to the underside of an aluminum tank or block depending on the unit type. They are not exposed to moisture. And they are grounded.

Note that replacing the power module and fuse has seemed to fix the issue in the field according to our dealer (ie no heater change or wiring change necessary). Or at least he has not seen it reoccur on the units he repaired.

Eddie

Hi Trinitron here,

I refer you to my comments in my previous reply #21. I bet that your original fit fuses are not rated for the Australian voltages (and considering that line-to-neutral volts appears across only 1 of the MOVs).

I reckon the 1 MOV across the active pole is conducting (which they are supposed to do to in order to limit any surges or spikes) and the resulting current causes the fuse to blow. Whether the MOV is conducting because it has switched on or has simply failed remains for you to determine from failed units.

I further deduce that in replacing the failed items, the distributor has used parts that will be suitable for the job rather than the original components. This may be more to do with parts available rather than because they know better than the original designer.

We had the reverse problem when we tried to get equipment UL certified... fusees that were perferctly good for 240V were not useable in the American market place simply because they weren't cleared for use on 110V! (UL inspectors comments not mine!)

Mr. Hunnel,

Having studied that circuit I think Avi-Tech may be right.

In the first place I don't see why the designer of that circuit found it necessary to include the gas tube or the MOV's, all surge reduction devices. There is nothing in that circuit that, unlike solid state computer and other gear, is very vulnerable to a surge, provided of course that the transformer insulation has a high enough voltage rating so as not itself to break down.

I think your problem is in the surge protection devices which would also explain the variations in the breakdown scenario. The only way you could get dead short across those fuses is a shorted gas tube or MOV's, except for the transformer primary which is not a good candidate for a short of that magnitude.

What I would do in your situation is have a test bench set up consisting of drop in sockets for the MOV's and the gas tubes, and connect those to an adequate load and feed the whole thing from an auto-transformer of sufficient voltage to approach within eighty or ninety percent of specified break down voltage, you will need a voltmeter in the circuit, and having enough ampacity to sustain this test.

I would then start testing starting below 220 and then advancing the voltage to 80 or 90 percent of breakdown specs.

My bet is that you will begin finding your problem. Of those passing I would plug them into a board of parallel sockets, set the voltage ten or fifteen percent over what they would see in normal operation, leave them that way overnight, and see how many drop out there.

Alternatively, although if this is indeed not the problem not good for customer relations, I would simply pull all those MOV's and the gas tube, which serve no useful purpose in that circuit and that application, and ship the product.

The surge reducers may have been intended to protect the computer circuit you say is attached to the transformer secondary. You might reasonably have a use for them there where they would not be looking at high voltage except for a surge, but my bet is the transformer itself would be sufficient protection.

Want to bet your problems will disappear?

Want to bet your production end is not doing individual quality checks of components as they are received from your suppliers?

I would begin testing those surge protecting devices.

j.

Looking at your schematic... tie the lower power in to ground at the power plug. Assume 220 vac on the upper pin of the power plug (for ease of discussion)...

First... what is the device after the two fuses? We now have the lower contact at ground along with the contact on the right side. What voltage is the device? If it shorts, it will take out F1.

Now... under the test conditions described above, both top and bottom of MOV2 are at ground... leaving 220v across MOV1. Same thing... if MOV1 shorts, it will take out F1.

Regarding the setup, the inverse would similarly hold true... If you ground the upper power in pin and provide 220 vac to the lower power in pin only you would take out F2 instead of F1.

You can emulate this here in the states by using a 110v -> 220 v isolation transformer and grounding one side of the 220 v. I suspect that the Australians are feeding you 240vac on one power pin and ground return (equivalent to our neutral) on the other pin.

Sincerely

Bill

I disagree with your initial comments completely, if the neutral is grounded at the substation, then grounding it again (assuming that the neutral is the lower (white?) wire) is going to make a loop and may cause problems, hum etc......

If the neutral has been connected to the black wire, then you make a short circuit.....

May I suggest that you think it through a little more carefully first?

I think that your problem was solved long before you sold your first unit in Australia. When US built products were first exported there, I'm sure some enterprising people developed an adaptor that would allow US equipment to be used in Australia. Why not purchase an adaptor from a quality manufacturer, find out what is in it, and build the same parts into your equipment. This would allow you to use a product that works here properly, and not have to redesign your whole product.

I wonder if there is any transient or spike in the power supply which may induce a high voltage causing violent explosion of the fuse . It may happen due to many reasons but before going into details you may try using a voltage stabiliser or a spike buster with a filter circuit for smoothing out any such transient , before connecting the power line to your equipment . I will be interested to know the result

I agree with another poster, that the surge arrestors are not working correctly (quality problems? tolerance problems? Incorrect voltage for 240 volts supply?) and are sometimes shorting out and blowing the fuse(s).....

You are so right Masu and the only thing I did not query, since his diagram did not supply the specific MOV or discharge tubes, so we could not check were they rated high enough to withstand the spikes they might encounter there in Australia.

So, indeed given that, he does need to quality check those devices as well as assure they are rated high enough for your conditions.

But actually there is no need at all for them since nothing in that circuit is voltage sensitive providing the transformer insulation is adequate. Sort of a case where overbuilding, which ought to provide positive margin, turns around and bites you because the overbuild components are inadequate.

j.

Some really good points, thanks.

Thanks MASU!! I believe that your Australian System is much like our 110 volt system in that the neutral line returns to the power source transformer (say on the utility pole) and is GROUNDED AT THAT POINT. I was trying to emulate that scheme in my earlier post. I know that in the US, if you put an ohm meter between neutral and ground in a NON-ACTIVE power plug (with all circuit breakers tripped) that you read a very low resistance.

Does my concept described above agree with your knowlege??

I suspect that if the original poster used the same schematic that they use in their US devices (only with all parts beefed up for 220v and voltage spikes etc) they might be home free.

Sincerely

Bill

GA. I gave you one too!

This fits in with my UK/German experiences and US built equipment, in fact, fairly early on in this blog I mentioned such devices rated too low, even 600 volts working voltage is too low. I used to use 1000 volt devices in the UK and Germany and had no further problems.....

Its interesting that you mention distances as being the reason for 240 volts, I thought that it was being part of the British commonwealth was the reason!! But the UK has no need to send 240 volts any great distance, but it does mean almost half the copper for the same power though!!!

For long distances, you need to transform up to a high voltage (to reduce losses) and then transform down at the point where it is needed.....

Reading Andy's response brings thermography imaging to mind. A good camera unit can provide sequencing of images (a movie) from initiation to failure. Clearly there is a noticable temperature rise in the victimised part. Thermography will give you a point from which to source the cause. You are looking for the 1 or 2 images that disclose the failure event in a failure reconstruction.

Bon chance,

Ralph

Right on Andy, our system is identical to the UK system

Reduces the cable size for the same power required at 120V, over long distances it reduces the cost of transmission lines and voltage drop.
Over very long distances we use 11KV, 22KV and in some areas of very low density use a single HV wire with a ground return ( mainly used in remote farming areas), a small transformer is placed on the pole at the farm site.

G'day Bill,

Yep. It's called a MEN or Main Earth Neutral link and keeps the neutral as close as possible to the local ground potential as is practical. You then have three active lines each 120° phase shifted from each other that give you 416 V phase to phase.

G'day Andy,

• Its interesting that you mention distances as being the reason for 240 volts, I thought that it was being part of the British commonwealth was the reason!! But the UK has no need to send 240 volts any great distance, but it does mean almost half the copper for the same power though!!!

Undoubtedly that was also a contributing factor.

If you stick with a standard thickness cable by doubling the mains voltage you can send it four times as far without increasing the loss. When you convert this to a grid application it means you only need 1/16 (1 ÷ 4²) as many 11 kV to 240/415 V transformers. That's no trifling gain especially in Australia which is about as big as Europe or continental USA but with only 21 million people.

So the end subscriber gets all 3 phases along with neutral?

I wish they had that here in the states. If you want 3 phase here, they have to add the transformer and charge you BIG $$ for it. Not money I was willing to spend for equipment I _might buy 10 years from now.

Much Thanks

Bill

I think MASU and others might be onto something here with the MOV's (and I gave MASU a GA for it too.). I've been thinking along those same lines myself over the weekend. The old thinking on MOV's from decades ago when they first were introduced were that they would always fail open when they died and not kill the circuit when they did, but as real world experience has been accrued, we are finding that more and more, they can fail in a short circuit mode once in a while too. MOV's also have a finite number of spikes and a finite amount of power they can dissipate before they flop on their backs and wiggle thier little leads in the air. And it is cumulative. Therefore, if the MOV's are marginal for the higher voltage application, and the number of spikes are much higher and stronger, then you may be setting them up for early failure. I would bet that MOST of the MOV's have failed, and only a small fraction have failed in a short circuit. Your circuit just would not notice if they did. I've found that neon bulbs are pretty good for serving both as a HV gas discharge tube and a power indicator. I usually put one in paralell with an MOV to help protect it from the larger spikes, and to give a minimum amount of protection even if the MOV fails for that reason.

Have any of the failed power modules been returned to the factory for rebuild/eval? It might pay to see if you can get one shipped back the next time one fails in order to try to figure out where the short is, because you most definitely have a dead short. that is the only thing that could possibly cause that kind of explosive reaction. Switching to ceramic fuses in the interim isn't a bad idea either to prevent such an explosion.

some links on MOV failure modes for your perusal:

http://powerelectronics.com/mag/power_thermally_protected_movs_3/

http://cerc.eng.usf.edu/std_individual/Stelios.pdf

http://ieeexplore.ieee.org/Xplore/login.jsp?url=/iel5/30/4341546/04341587.pdf?arnumber=4341587

Most of the MOV's I have seen that failed open, the only thing left was the 2 legs sticking out of the PCB where the MOV usually sits.

The rest of the time, it failed short, with a face blown off, cracked, or with a missing face and a nice hole blown thru it.

Hi Sciesis2

· So the end subscriber gets all 3 phases along with neutral?

Well sort of. Normally domestic residences don't need three phases so they get a single phase with a neutral. Although you can have three phase power connected if you ask for it. There is a charge for having it connected but it's just a matter of running two extra conductors to your main switch board so it's nothing like the charge you would need to pay if there were an additional transformer.

Just a thought, I wonder if this MOV is the "failing fuse" that the distributor was talking about? Maybe he has made a mistake in identifying what is actually getting damaged?????

A possible cause of random failure can be the ripple control frequency which is sent down the powerlines to switch loads such as hotwater systems on and off. It is typically applied several times during peak load periods. There are multiple channels in a range from 400hz to 1200hz when I last checked many years ago, there may be even more channels now or apparently redundant channels such as the air raid siren channel may have been reallocated.

Hi, Emjay4119!

Wow! That's really interesting, and amazing to know. I hadn't heard of it before now in my limited contact with this kind of technology. Live and learn! Thanks for the info.

Mind you, the OP did mention that the problem was more than just sporadic in nature. "Almost without exception, all the units we have sold to Australia have had a catastrophic failure in the power module." So a ripple control frequency's unlikely to be the source of his problem, as I understand your explanation. No?

Mark

That is why I posted the story, all plugged in gear is exposed to ripple control frequencies several times per day. The length of time between switchings is largely dependant on load and of course how much spare rotating capacity is available at the various power stations.

Flouro ballasts often sing when the signal is being sent. Noise in amplifiers often increases and I also think some brands of CCFL bulbs die from it eg., Crompton.

When I saw the gear for transmitting the signals as an apprentice WTF back it was an MG set. Even for hot water system control several channels are used.

As an aside, the greenie wankers want to ban electric HWS but they are so misinformed that they think it will "save carbon". The truth is controlled tarrifs even out demand to match production and lower fuel useage. During the "Earth hour" propaganda fest earlier in the year all that happened when the load came off, was the forced venting of steam at the power stations. You can't just turn off a gigawatt turboalternator, the bigger the set the longer it takes, days in fact. I remember how cranky the power station maintenance engineers were when forced to use Tennyson power station as a peak load station by bringing 30mw sets on line in just 3 hours then dropping them at the end of peak.

The controlled tarrifs reduce those problems and of course make harvesting of renewables more viable.

The day the greenweirds get their way and force gas on the public will be a bad day for us all, especially for the environment.

Anyway I'm heading off topic.

Hi, Emjay4119!

I think it's OK to vent a little bit. It's a tough situation.

Everyone wants to be as green as he/she can; and when those [--who are uninformed about just how green some technologies are, or have become through their own industrial evolution (or even by accident!)--] see big machinery operating, they have no idea of the intricacies involved in calculating its carbon footprint.

Instead, their lack of understanding causes them to undertake a kind of a witch-hunt, in which they naturally assume a large carbon footprint because they have not had the time to, or the education to, follow the engineering processes involved in a meaningful way..

I think if you questioned them closely, those same individuals could not even offer a cogent answer about the intricacies of why 'green is good'...they've been informed it is by others who either have an understanding or an economic/political agenda best supported by green thinking. The ordinary bloke's rationale is often superficial at best. He's just trying to be conscientious. And "green is good" presupposes that the opposite is bad, which is a no-brainer, so it's a really easy warpath to head down.

The conflict that drives us nuts is that you can't blame folks for wanting to be green. But in the name of that quest, their attacks composed of unsupported evidence and knee-jerk reaction to something for which they have either half an explanation (the 'bad' half) or, more often, no real data is infuriating to those who have evidence and understanding to the contrary.

Another disquieting aspect of this blinkered thinking is that some of the really important issues that might be related to the green quest get put aside for the bandwagon silliness.

Try to not get too involved in instances of this "normal" foolishness, or it'll drive you nuts! Each time I see it, I just make a statement in direct response, and then let it go until the next time.

Mark