Member postings for Robert Laurenson

Robert

Yes, I was thinking of the voltages and phases measured to the existing neutral. I can see that for a delta connected supply, it would work as you say, so your idea of a delta/ star connected transformer would give a neutral and correct the voltages.

Regarding the supply capacity, as well as the kVA rating there is also the effect of any sudden changes in load such as welders and motors. Your DNO may have already told you what maximum welding and motor starting currents you can have. There is an Energy Networks Association (ENA) document Engineering Recomendation P28 which DNOs use to calculate these figures ( though they may have their own policies based on this).

**LINK**

Stuart

Edited By Stuart Smith 5 on 20/07/2021 22:57:59

Edited By Stuart Smith 5 on 20/07/2021 22:59:02

Robert

As someone who worked as an electrical power engineer for my local DNO ( or electricity board as it used to be), I would suggest you check with SSE to see what load and motor starting currents you can take from your existing supply. As per my post in your previous thread on buying a lathe:

”Robert

Although the fuse carriers on your main DNO fuses may be labelled as 100A , you would be advised to check what current you can actually take from the network. I used to work at Electricity North West and the maximum supply capacity there was specified as 20kVA for a single phase supply ( ie 80A). The other issue may be that the rating of the pole mounted transformer may be a limiting factor. Also there are limits on voltage fluctuations caused by motor starting currents or welders (see ENA ER P28).

Stuart”

Regarding the ‘Phase Perfect’ - it seems to be anything but perfect.

It is clear from this diagram that the two existing phases are used as they are and the third phase is generated electronically. So the two phases will be 180 degrees apart and presumably the extra phase will be 90 degrees from them. The phase to phase voltages will be as per the supply (ie somewhere in the 450 to 500 volt range depending on the loads on the network etc)

Stuart

Make sure your electrician and supply company are happy with it before you spend the money. It has NO UK / EU approvals at all. That means it may not be legal to use. I'm not sure what the current requirements for fixed industrial electrical equipment are. If it is a non-industrial installation it has to be approved equipment.

Robert G8RPI.

Edited By Robert Atkinson 2 on 20/07/2021 21:11:50

This is an interesting thread, lots of opportunity for the magic blue smoke to leave!

What is a split phase 480V AC supply? It seems to be from posts that it is two 240V supplies but independant of each other so you do actually get 480V live to live? Where on earth does it come from? This arrangement of two supplies that can be used live to live seems to be an American thing, 110V to 220V.

Talking about 30kW output, have you costed a 30kW transformer? Might be a long way towards the 3ph install cost.

Don't forget that the only way to convert single to three, or multiple, phase is by using energy storage devices, capacitance, inductance or inertia, and inertia is the cheapest.

Seems to me that buying a diesel generator is much the simplest solution, something about 60kW is about £4k secondhand. Again, be aware of the synchronous reactance which is what makes a 10kW generator power only a 5kW load. For the plasma cutter you don't need AC, since it works internally from a DC bus. Similarly for 400V 3ph VFDs, they all seem to use an internal DC bus and the AC doesn't do anything.

A 100A 400V 3ph supply is about 24kW, seem to be beyond that?

Hi John,

Thanks for the link. It's certainly not as originally described and has some key components not shown in the installation manual. That said the Patent i terrible and does not reveal anything about how it actually works. Presumably it is using PWM and the output capcitors (not shown in manual circuit) are doing a lot of the work. Thi is supported by that that they have to be reguarly checked / replaced.
It's whats not in the patent and specification that would bother me. No output voltage spec other than about the same as the input. No output power factor range. No minimum load. No step load change response. Some of the patent claims are a bit broad e.g. basically any circuit with a phase controlled input bridge and polarised storage capacitor would breach it. Lots of prior art to get around that one. The patent does not mention PWM or if they don't use PWM how they generate the waveforms. All in they must have some pretty advanced math to generate the required waveform for zero to unity PF over 0 to 118kVA. I've recetly been working with some custom <50kVA converters and the supplers of those have struggled to meet specification even with full 3 phase bridges and limited load power factor.

It's also does not appear to be suitable for UK use. Standard is 60Hz and there are no claims for any safety or EMC approvals. They have the ELT mark on parts of documents but only their variable speed drives are listed and then to very limited tests

https://ramuk.intertekconnect.com//WebClients/ITS/DLP/products.nsf/vwSearch?SearchView&Query=FIELD%20ListHead%20Contains%20phase%20perfect%20or%20FIELD%20CatCode%20Contains%20phase%20perfect%20or%20FIELD%20Title%20Contains%20phase%20perfect%20or%20FIELD%20ProductInformation%20Contains%20phase%20perfect%20or%20FIELD%20ProductInfo%20Contains%20phase%20perfect&SearchOrder=1&SearchMax=1000&SearchWV=FALSE&SearchThesaurus=FALSE&SearchFuzzy=FALSE

If any of the machines to be powered have a neutral connection (5 wires) then a delta/star transformer will be required.

Hi Robert,

Speaking with Phase Perfect just now, and they can supply it as 50hz, so no issue there.

And i will have to run it through a transformer anyway due to the 480v, i need it down at 440 ish to run my equipment.

To be honest i do think now that its the only way to go.

You seem to require a three phase supply in your workshop to run several machines when the only input is single phase. This would need a large converter, which would be expensive and might cost more than individual VFD's for each machine. Also, individual VFD's can be programmed to suit each machine for motor start and stop characteristics and speed control, plus forward and reverse if needed.

Having a three phase supply from the mains would seem to be the best long term solution for such a large workshop.

Edited By old mart on 20/07/2021 18:26:09

Hi,

The Phase Perfect system would be better called Phase Imperfect. They do not say anywhere on their datasheet what the output phase relationship is, but from the description it is clearly not 120 degrees or balanced. Two are 180 degrees apart (the incoming line) and the third is 90 degrees from these. Unlikely to give smooth torque from a motor desigined for 120 degrees. Also note if any of the machines have a single phase 480V load interanally you will have to ensure they are across the incoming phase. If any require a Neutral connection You will have to add a delta star transformer. This is more cost.
I would not bother with it for machine tools. Probably passible for basic prime movers but even things like pumps could suffer damage from the torque variation caused by the mismatch beteen the mechcanical angular pole spacing and the electrical supply phase.

Individual VFDs per machine (even multi motor ones as long as you keep the "speed" at 100%) is likely to be a better solution. Or get the advantageof variable speed and fit a VFD per motor.

What country are you in?

Robert G8RPI

Edited By Robert Atkinson 2 on 20/07/2021 15:51:40

Best place to start is to describe what you are trying to do. Are you intending to run a 3-phase motor from a single phase supply, or create a substitute for a utility 3-phase supply.

I'm not convinced that capacitors on the AC output will help with start current.

Personally I went with having a proper 3-phase supply installed at home.

Andrew

Robert

A version of the common 1340 Taiwanese built lathe I think. The Grizzly Tools manual probably applies so may be worth picking up the PDF from their website.

Generally ISO 32 hydraulic oil with anti wear additives for the headstock, ISO 68 way and bearing oil for the bed, feed-screws and sides. Most seem to suggest ISO 68 for the gearbox and apron but ISO 32 for the apron is not unknown. Possibly related to whether or not it has a pump feed from the apron to the bed, ISO 68 may be a little too heavy for the pump.

I use Castrol Hyspin AWS 32 and Magna BD68 bearing / slideway oil on my machines following advice from Castrol technical many years ago and have no reason to dispute the advice. Don't use ISO 68 slideway only oil in the gearbox or apron as it will be excessively sticky. Dual rated, like Magna, is probably best but for our use an ordinary ISO 68 oil should look after the bed and slides just fine. Inspector Meticulous would say oil them before starting work, Ordinary Machinist says don't let things get dry.

Clive

Edited By Clive Foster on 30/06/2020 16:59:57

A motor idling off-load will typically use 5 to 10% of it's rated power, so say about 1kW.

But maybe it's time to think about getting professional advice? The requirement has evolved from the best way to power a lathe that happens to have a VFD-awkward two-speed motor into a workshop containing several hefty 5kW items. This is crossing the great divide between a domestic set-up and a commercial operation.

In my single-garage workshop I've arranged the electrics around it's bog-standard domestic 13A supply. Although 26A is theoretically available because the socket is on a ring-main, I limit myself to running one machine at a time, and they are all sized within normal 240V 13A limits. This works well because it's just me, I never run my mill and lathe at the same time, and I doubt I ever consume more than 2.5kW peak (10A). My machines are either single phase or 3-phase provided by VFD. It's not complicated.

It wouldn't do if I was busy and especially not if two or more people needed to use a combination of machines at the same time. In my workshop the pillar drill, belt grinder, band-saw, grinding wheel, mill and lathe together are too much for my wiring. Introducing a high power, high-voltage, or dual speed motor into the mix would need special attention, either a posh-VFD (not ebay!), more likely a rotary. Wouldn't be difficult to uprate my workshop supply to say 30 or 40A, (say 10kW) but I'd need an electrician. Beyond 40A my consumer unit and company fuse would need to be upgraded too.

My garage workshop supply is OK for my amateur use. Cheap and straightforward, but limiting in use and difficult to expand beyond my simple needs. This sort of ad-hoc arrangement isn't a good way to power an expanding time-is-money business, for example staff queuing at machines due to power limitations wastes a fortune in wages. And, although the cost of the various single-phase to three-phase solutions are individually affordable step-by-step, the cost adds-up. There's a point at which it's cheaper to bite the bullet and have native 3-phase installed. Then powering 3-phase machines of any type ceases to be a problem.

The question is, how much would it cost to have 3-phase installed? Some forum members have had it done for perfectly reasonable money, others have been quoted ouch thousands. Seems to depend on how much work and disruption is involved, and if the benefit can be spread across other nearby consumers. Digging a trench along a busy 'A' road might be considerably more expensive than running overhead wires on existing poles to a new transformer. You would have to get a quote.

Tricky job starting a small business where the best must be made of limited resources. However, if the endeavour has a confident future and is going to expand, worth doing a Business Plan and, depending on the numbers, approaching the Bank for a loan.

Dave

Robert

One hears tales of rotary converter efficiency being in the 80% to 90% range with idling power consumption in the 5% to 10% range. Given the number of variables and interactions involved I guess its one of those "it all depends" things. Seems reasonable to expect your proposed 18.5 kw rotary to cost in the region of £5 to £10 per 40 hour week just spinning in the corner.

However the world is changing and I'd strongly urge you to set out a spreadsheet and do the maths for various combinations of supply devices for your machines with particular attention to how long you are going to be using the power hungry ones for. If the hard ones are only going to run for half a day a week in one continuous batch of work getting a used diesel powered gen set just for those might make a lot of sense.

I believe some 3 phase VFD boxes can accept a single phase input if derated. Still needs a transformer to boost your voltage or, possibly, they can use your split single phase set-up to get the voltage. Time to talk to the specialists and find out what can be done and how much it will cost.

My feeling is that one VFD per machine is now the bench mark for costing in smaller workshops, say up to 10 machines, if proper 3 phase power cannot be got.

Certainly when I put my big VFD box in back around 2006/07 (as a temporary expedient pending getting proper 3 phase laid in) because the small pseudo rotary I was using didn't have the power for more machines that or a similar size rotary for whole shop powered were the only viable options. One VFD per machine would have been impossibly expensive.

Fast forward to 2020 I have now got a 3 phase incomer but the professional electrician installation costs, extra components and commissioning charges aren't greatly dissimilar to going one VFD per machine, I have 10, even factoring in a couple of motor changes. I may well just choose to write off the new incomer costs. Especially as getting a sparky to actually turn up and do the 3 phase installation job seems to be impossible.

Clive

Edited By Clive Foster on 17/05/2020 09:50:57

A good rotary converter would run about 95% efficency at rated load. Most of this will be fixed lossses such as bearing drag and windage. I woud expect that a 185kW convertey would consume about 1kW off load. However you need to think kVA too because that's what the electricity meter responds to and can be a lot higher for an off load motor

If you are going to be running 3 or 4 5kW machine tools at the same time you should probably get a 3 phase supply. Otherwise modern solid state converters are probably the best solution. You don't HAVE to run a VFD att different frequencies, if you run it at 50 or 60 Hz it will run any machine if the voltage suits the motor.
The issue many have mentoned is getting a "400" volt output. from a 240V input. There a number of ways to do this. Easyist is a solid state converter specified for the task. These tend to be more expensive. As you have a 480V supply and a 3 phase in 3 phase out VFD converts it's input to DC it is entirely possible to use an exernal rectifier and filter capacitor to feed the VFD's DC bus. If the DC bus will take 680V DC you can use the 480V supply directly. Otherwise you need to drop the voltage closer to 418AC / 580DC. Two standard 30V dual secondary 500VA transformers wired in buck will drop you 480V to 420V.

However doing this requires some knowedge of power electronics and motors. The easy / safe solution is Clives number 3 suggestion to change the motor and use a VFD. It will pay for itself in power bill savingscompared to a rotary converter over the years and make the lathe more saleable of you don't keep it.

The same goes for other 3 phase machines. Try to buy one with a low voltage or Star/Delta motor or just change it. Don't forget you can sell the old motor to get some cost back.

I would not consider a rotary converter unless it was free and preferably delivered for free.

Robert G8RPI.

Edited By Robert Atkinson 2 on 17/05/2020 09:48:14

This supply scheme is similar to that used in North America for domestic supplies. The NA one is 115V- 0-115V 180 degree phase shift to each house. It is used in some remote areas in the UK. Two wires are taken from the 3 phase high voltage (probably 11kV) supply and run to the remote location. Thi is of course single phase as there are only two wires. For each small group of consumers there is a transformer. In the simplest solution this would have a single 240 V (41.66:1 step down) output winding for the whole load at 240V. However the physics of transformer design means that a pair of windings connected 180 degrees out of phase use less core material. Splititng the load across two windings also means thinner wire can be used making winding easier. This scheme is called "Split-Phase" and uses a single (20.8:1 ratio) winding with a center tap. The center tap is the neutral for both supplies. Normally each consumer would only have a single 240V connetion but heavy users may have two. The voltage between the phases is 480V (if they were 120 degrees apart it would be 415V)
It is not possible to simply generate 3 phase from this type of supply. There may be confusion with two phase 90 degree systems (phase quadrature) which can be changed to and from 3 phase 120 degree using a pair of transformers in a arragement called Scott-T. To run a 3 phase motor you will need a converter either a electromechanical (e.g. transwave) or solid state (VFD) type. In theory you could feed a VFD with both phases via a pair of rectifiers but it's hardly worth it for such a small motor.

Robert G8RPI.