|May28-12, 02:43 AM||#1|
Using a US manufactured digital phase conveter in the UK
My home workshop has three woodworking machines, all fitted with dual voltage 3 Phase motors, currently configured for 415V 50Hz. My workshop power supply is 230V single phase 50A. I have been using a static converter to provide the three phase but I would now like to upgrade to a digital phase converter manufactured by Phase Technologies LLS in the US. Web address and specific model phaseperfect.com/files/pt330specs.htm
The makers are helpful but I am not qualified to understand their replies.
I understand that static and rotary converters are far from perfect and would like to move to and advance technique that seems to offer a perfect solution providing the change of frequency and input voltage can be accomodated.
Thanks in advance
|May28-12, 10:12 AM||#2|
reading their datasheet leaves me with two questions.
1. OOps my mistake - They say it's useable 50 or 60 hz so that one's answered
2. They say on http://phaseperfect.com/files/pt330specs.pdf page 2 that its 3 phase output power is same voltage as its single phase input .
"Voltage Equal to single-phase input voltage – 187-260 volts"
and your motors are 415 volts? Your input is 230? Sounds to me like you'll have a mismatch.
|May28-12, 10:32 AM||#3|
Thank you for your reply.
My motors are dual voltage and can be changed from 415V to 230V 3 phase.
|May28-12, 07:53 PM||#4|
Using a US manufactured digital phase conveter in the UK
Check the "KVA code" on your motors, it gives you their starting current. It's usually several times running current.
Make sure the electronic gizmo has capacity to start your motors.
Good luck !
|May28-12, 11:55 PM||#5|
Surely not that old!
I will check the motor kVa - I note that this converter accomodates a 4 second overload of 150A.
One final question (I hope) Can you open the following link (phaseperfect.com/files/op_inst_pt.pdf) and look at Fig. 6; my limited electrical knowlege seems to detect the need for an additional transformer between my power supply and the L1 & L2 inputs of the converter! If I am correct, Phase Perfect will be able to supply one but to minimise shipping costs I would prefer to source one in the UK - are you able to advise details of a suitable transformer.
|May29-12, 12:14 AM||#6|
Just found this on another site and it seems to clear the fog on my understanding of the US power system but not how Phase Perfect create 3 Phase.
A split phase electricity distribution system is a 3-wire single-phase distribution system, commonly used in North America for single-family residential and light commercial (up to about 100 kVA) applications. It is the AC equivalent of the original Edison 3-wire direct current system. Its primary advantage is that it saves conductor material over a single ended single phase system while only requiring single phase on the supply side of the distribution transformer. Since there are two live conductors in the system, it is sometimes incorrectly referred to as "two phase". To avoid confusion with split-phase motor start applications, it is appropriate to call this power distribution system a 3-wire, single-phase, mid-point neutral system
|May29-12, 03:32 AM||#7|
I'm an electrician, and as far as I can tell, these seem to be a good unit (though I have never used one).
The biggest question is how much power you need to run your machines. You need to work this out so that you don't end up choosing a unit that's too small, and also so that you don't overload your supply.
A 3 phase machine rated at 10 Amps will draw a lot more than that through the line side of your converter (from memory you multiply your current by √3, but that could be wrong).
If you've got machines with dual voltage connections, they will have dual voltage windings or tappings inside, you won't need a voltage converter.
Motor startup shouldn't be a problem with the high inrush currents it can provide; although you may need to install a 'd' curve circuit breaker on the supply to your shed if it starts tripping on startup.
|May29-12, 07:53 AM||#8|
|May29-12, 10:15 AM||#9|
YES! and I went to school with A. Einstein but he grabbed all of the brains!
On this link xxx.phaseperfect.com/techinfo.htm "Operation and Installation Manual - PT Series" diagram 6 shows a diagrammatic of the US electricity grid supplying 120V x two to L1 & L2 of the converter - I presume that I could achieve the same inputs with a 230V transformer with a centre tapped output & 2 x 120V.
If I am correct; next question, can you suggest the specifics including the required kVa of a transformer that will do this job.
|May29-12, 07:39 PM||#10|
Maybe Sophie can help us out here too. I dont know how British power is delivered.
First , the figure you reference shows a third wire connected to "ground" at both source and at the unit.
http://phaseperfect.com/files/op_inst_pt.pdf fig 6
That might represent either an earthing connection, or a neutral connection.
(The difference between an earthing connection and a neutral connection is the neutral normally carries current; while the earthing one does not- it's there only for safety during faults.)
I suspect it is an earthing connection. Many 240 volt appliances in US do not use a neutral.
Page 3 shows two line connections and one ground connection, notably absent is one labelled 'neutral'.
Whether this is a current carrying connection should be verified by a phonecall to Phaseperfect, or their UK representative..
Sophie will know how British power is earthed. US power is earthed as in fig6 top sketch.
I'm going to assume having done a quick search, that in England one side of your incoming 240 is earthed and called "neutral".
Sophie - plz help !
I am going out on a limb here, but i think your Phaseperfect gizmo needs only the two incoming power leads and a safety earthing conductor. That conductor must be large enough to trip the branch breaker in case of fault so make it the same size as your power wires..
If i am wrong you will have to create a center-tapped 230 volt supply.
The 100% surefire way is to use a transformer rated same as the phase converter, 230 to 230 volts ~10kva with centertapped secondary and earth that centertap..
That seems awfully cumbersome and i will be surprised if it's necessary. This seems a sophisticated machine that's aimed at international market. Surely they are too smart for that.
This should be verified by a phonecall to phaseperfect, or their UK representative..
A question well phrased is half answered
If any of it is unclear to you please advise. I'm a Yank, you know, and we are not known for precision and clarity in our use of English.
ps speaking of British hobbyists - i recently read (again) "Trustee from the Toolroom". Might you know of it ?
It was one of the formative events of my youth.
|May29-12, 07:47 PM||#11|
post- ps if it turns out a transformer is neeeded i'll help pick one.
Also did you note their caution about output being delta only ?
In your case, one output terminal will be at neutral. See block diagram page 6 of PDF, manual page 1 (right after iv).
|May30-12, 12:37 AM||#12|
Good morning Jim
First let me clarify the UK domestic supply system. At street level the supply utilities distribute 3 phase, 415V ac power, a neutral, the protective Earth is provided either by ground spikes or via the utilities armoured cable sheath. Each phase to neutral provides 230V.
Each dwelling will have a 1 phase 230V supply (one of the three phases), a neutral plus the protective earth. The utilities balance the 3 Phase load by using a different phase to neighbouring properties.
Three phase power is only supplied as standard to factories and other large users.
Back to the Perfect Phase device. My latest question to Phase Technologies is :-
I have been continuing to study your documentation and believe that I am close to understanding how the US provides electrical services to small consumers and how this relates to the supply side requirements of the PT 330. On the diagram (6) it shows a transformer providing the two hot lines at 120 V Can you specify the kVa of a centre taped transformer that would transform the UK’s 230V into the two 120V lines.
You do not need a transformer. You can supply 230V to one leg and 0V to the other.
The previous email :-
Good morning Steve
Sorry but I need further clarification before ordering the PT330. Please appreciate that I am a clock maker/cabinet maker so my electrical knowledge is limited.
Please let me explain. My supply is 230Vac 50Hz and 50A. This consists of L1 (hot) (230V), Neutral & protective Earth.
All of my motors are dual voltage without neutral; the manual states 4.0 HP (3.0kW) 220-254/380-440V.
A/ The UK supply is 50Hz, does the Hz difference rule out the use of your convertor in England.
B/ What would need to be done electrically to connect the UK single phase 230V to the input of the PT330?
Do hope that you can find time to conclusively determine the suitability of using the PT330 in England.
A. We can operate at 50Hz
B. All phase converter outputs are Delta. Input at 230V will give you 230V output. You would need a transformer on the output if you required 415V.
phaseperfect.com/files/op_inst_pt.pdf Here is the install manual.
What is the significance of the output being delta only?
|May30-12, 05:41 AM||#13|
It's interesting how the two systems developed and why. I am sure it's to do with population density and original choice of domestic voltage. In the US they couldn't afford to distribute from a central point at LV so they use HV distribution and individual transformers on poles- designed to a price and hence the unbalanced primary. In the UK, there is mostly underground distribution from a local 'sub-station' and the earth is provided largely by the sheath on the company cable to the house. LV cables are seldom more than a couple of hundred metres and allowing the common neutral to float will reduce losses when the demand on the phases becomes unbalanced. The difference in supply voltages between US and UK further justified the different choices of the two systems. The UK doesn't use the split phase and domestic dual voltage that the US does. I believe the 240V option must have been a retro-fit in the US, which was introduced as domestic loads got bigger.
|May30-12, 06:59 AM||#14|
Thanks fellows ! UK distribution now makes sense.
Frank i tend to be always a paragraph behind any conversation. I have grown accustomed to it though.
Okay - so they've already confirmed they will accept 240 between L1 and L2 with one side 'grounded'( i prefer term 'earthed') . That's very sensible of them.
So the converter should be happy connected to your supply, 240 single phase one side earthed.
Label the three vertices T1 T2 and T3 .
That's a scale drawing of your three phase voltage, 100 volts per inch.
Now observe from installation manual's block diagram on page 1 (page 4 of PDF) that:
T1 will be connected by the contactor to L2; and
T2 will be connected to L1; and
T3 will be created by the electronics .
T1 and T2 are 240 volts apart, that's defined by input L1 and L2.
T3 is placed by the electronics equidistant from T1 and T2. The electronics places it 240 volts equidistant.
Notice there's no neutral or ground. The gizmo doesn't really need them, it would work in an aircraftcraft or on the moon.
So now add to your triangle an earth connection at , say L2.
Nothing really changes so far as the converter's electronics are concerned.
Your motors will see T1 "earthed", but they won't care so long as their insulation is sound.
Now back to your triangle
Now add arrowheads so that the triangle looks like it's rotating CCW.
Now our graphical representation of the 240 three phase voltage has become a "Phasor diagram".
All that means is the arrows now indicate phase angles of your three voltages by their direction on the paper.
Now locate the center of your triangle/phasor diagream, the point in middle equidistant from all 3 vertices.
IF there were a neutral that's where it would be.
The Phaseperfect folks did not bring out a neutral, in fact may not even have fabricated one internally, so there just isn't one.
That's the only significance . If you need a neutral you have to make it yourself.
Now if you wish draw another phasor diagram with sides 4.15 inches long.
That's utility power. They hand to you one phase and neutral as you have already described.
By grade school geometry you can show that distance from any vertex to neutral will be 4.15/√3 = 2.4 inches.
So your Phaseperfect converter will hand you a three phase triangle, 240 volts per side with one vertex earthed instead of its neutral earthed.
That should be just fine for motors. On low voltage connection they'll be wound delta anyway.
If you have a high inertia load like a planer you might start it first.
I apologize for the length of this post. I think in pictures and words come with great difficulty. But i try to paint a picture in listener's mind. If i've meandered offtrack please call me out on it.
Sophie - you are better with words than i, if you improve on this i'll be honored.
Probably there's a ten word answer just it didnt come to me.
|May30-12, 07:18 AM||#15|
Wiki suggests it's a vestige of the early Edison DC systems, which you fellows may not have had to endure.
I dont remember them but worked with some electricians who did.
|May30-12, 07:20 AM||#16|
Just one comment before I digest you full reply - The UK house supply is Line (230V), Neutral (0V) and protective Earth.
I appreciate that the N is probably grounded or Earthed by the supplying utility at their district transformer but never by the user.
Does this affect your main comments?
Youngish in spirit, Frank
|May30-12, 07:30 AM||#17|
I'm not a power Engineer so I can't be too sure but, without a neutral (I.e. a delta supply) you can't use a single phase without having it balanced. If you earth one connection then the others will be higher voltage and with a bizarre 120 degrees between them. To overcome the lack of a neutral, won't you need another delta/star transformer?
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