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Norman Bain
06-30-2019, 07:47 PM
With my new found capability to cut angle iron tidily (click this link for detail) (http://bbs.homeshopmachinist.net/threads/79281-Metal-Cut-Off-Saw-(drop-saw)-modification) I set about doing what that project was intended for.

The unit now hanging on the wall is a rotary phase converter that probably weighs 50kg+

Essentially the "top hat" beam (as it is called here is Australia) is being leveraged to hang a frame in which the rotary phase converter now lives.

http://downloads.purposebuilt.com.au/NJB/DropSaw/DropSaw_12.jpg

I think this project was successful in making use of an otherwise unused space. Just look at those tidy joins :cool:

FYI: the frame is 750mm long x 400mm wide x 600mm high.

http://downloads.purposebuilt.com.au/NJB/DropSaw/DropSaw_13.jpg

The wiring in the shed is a work in progress. Plan is to route all the 3-phase from this point to a few sockets that will be situated where needed.

plunger
07-01-2019, 01:57 AM
With my new found capability to cut angle iron tidily (click this link for detail) (http://bbs.homeshopmachinist.net/threads/79281-Metal-Cut-Off-Saw-(drop-saw)-modification) I set about doing what that project was intended for.

The unit now hanging on the wall is a rotary phase converter that probably weighs 50kg+

Essentially the "top hat" beam (as it is called here is Australia) is being leveraged to hang a frame in which the rotary phase converter now lives.

http://downloads.purposebuilt.com.au/NJB/DropSaw/DropSaw_12.jpg

I think this project was successful in making use of an otherwise unused space. Just look at those tidy joins :cool:

FYI: the frame is 750mm long x 400mm wide x 600mm high.

http://downloads.purposebuilt.com.au/NJB/DropSaw/DropSaw_13.jpg

The wiring in the shed is a work in progress. Plan is to route all the 3-phase from this point to a few sockets that will be situated where needed.

A rotary phase converter in my country is unheard of. Is your electricity the same. We have single phase 240v 50hz and 380v 3ph.
Could you please tell us more about it

J Tiers
07-01-2019, 09:34 AM
I am impressed, most RPCs if hung on a sheet metal wall like that, could be heard 2 km away. The wall would act as a huge drumhead and make a lot of noise.

Yours must be very quiet.

Norman Bain
07-01-2019, 04:07 PM
I am impressed, most RPCs if hung on a sheet metal wall like that, could be heard 2 km away. The wall would act as a huge drumhead and make a lot of noise.

Yours must be very quiet.

Jerry, you make a very good point. Had not thought of that. Will give it a run and let you know.

Norman Bain
07-01-2019, 04:40 PM
A rotary phase converter in my country is unheard of. Is your electricity the same. We have single phase 240v 50hz and 380v 3ph.
Could you please tell us more about it

They are reasonably common both here in Australia and the USA. They have been discussed many times here on this forum.

There are some advantages and disadvantages compared to the solid state Variable Frequency Converter (VFD) approach. Advantage is more than one motor can be attached to the unit. Disadvantage; there is a hum due to the rotating motor.

Input is 240v single phase and output (of this unit) is 415v 3-phase in L1, L2, L3 and PE.

My understanding it is not that difficult for a reasonably competent person to make one of their own using a suitably sized 3-phase motor. To make one is even easier if you are prepared to spin the motor with a bit of rope (sort of like starting an old lawnmower) to get it cycling.

Here is a link to the manufacturer's site. (https://www.tortech.com.au/product/voltage-converters/single-to-three-phase-converter/)

Here is an image of the internals from the manufacturers site.
http://downloads.purposebuilt.com.au/NJB/DropSaw/DropSaw_14.jpg

J Tiers
07-01-2019, 04:44 PM
The rubber mounts I see in the picture will help a lot. There is already a fair bit of metal in the case, which would otherwise broadcast noise, so I imagine it IS rather quiet, and may be no issue at all. And, you can always set it on additional soft pads, in case there is more residual noise than you like.

Noitoen
07-01-2019, 05:02 PM
I don't know much about US power but single phase isn't really single phase. It's, related to your neutral, 2 phase so, it's easy to generate the 3rd phase using a capacitor and a motor acting as a kind of rotary transformer. Your power is supplied in a delta configuration with the neutral center tapped between 2 phase legs.
In Europe and South Africa, country where I lived between 1974 and 1980, power is supplied in a Y configuration so, I don't think a regular rotary phase converter will work properly. At least that's what I think.

Mark Rand
07-01-2019, 06:36 PM
No, that's single phase. Two phase has two voltage waveforms at 90 to each other compared with three phase's 120 separation. Any single phase system can run a static or rotary converter or an inverter, but it is useful to have an isolating transformer in the setup so that you can reference the output to the protective earth in a way that your country finds normal.

To Norman:- I bolted my dust extractor to the wall of the shed using vibration absorbing mounts and bolted the step-up and isolating transformers of my inverter set-up to it with their own mounts. They don't seem to transmit any noticeable sound to the outside of the shed as a result.

J Tiers
07-01-2019, 08:16 PM
I don't know much about US power but single phase isn't really single phase. It's, related to your neutral, 2 phase so, it's easy to generate the 3rd phase using a capacitor and a motor acting as a kind of rotary transformer. Your power is supplied in a delta configuration with the neutral center tapped between 2 phase legs.
In Europe and South Africa, country where I lived between 1974 and 1980, power is supplied in a Y configuration so, I don't think a regular rotary phase converter will work properly. At least that's what I think.

Adding to what Mark Rand said.....

the US single phase is normally obtained from one leg of 3 phase, vs neutral. That is the source, usually at high voltage. The local transformer, which may supply 3 houses, then has a secondary which is three wire, a center tapped 240V winding. The center tap is made the neutral, and is earthed.. Whenever you have a 2 wire source, there can only be one phase power obtained.

You may be thinking of "208V 3 phase", which is a nasty hybrid compromise. It uses 2 lines of a 3 phase source, plus neutral. It has the nasty characteristic of having 120V to neutral on both lines, but NOT being 240V between lines, which normal "240V" equipment in the US is looking for.

The 208V is NEVER supplied as 3 phase to a residence, at least not in my area. It may go to an apartment building as 3 phase, but no apartment gets anything but single phase.

That 208V source will provide 3 phase with a normal rotary phase converter, AND preserve the 3 phase neutral, but it will produce only 208V output unless stepped up with a transformer. While technically, there is phase information in the 208V, it is more practical to use a phase converter than to try to phase shift with capacitors, etc.

And, the idler motor is best referred to as an "induction generator" with respect to the generated leg. it is not proper to say it is a "rotary transformer", because a transformer produces no inherent phase shift. The "RPC" does, by means of the mechanical arrangement of the coils. The third phase really IS "generated", it is the back EMF of the motor. That fact accounts for why it is always lower in voltage than the incoming power.

Jim Stewart
07-01-2019, 09:56 PM
Adding to what Mark Rand said.....

the US single phase is normally obtained from one leg of 3 phase, vs neutral. That is the source, usually at high voltage. The local transformer, which may supply 3 houses, then has a secondary which is three wire, a center tapped 240V winding. The center tap is made the neutral, and is earthed..


Yes. Some call it two phase because there are two legs off the center-tapped transformer at the pole. Not right.

Small correction though, Jerry: it's not one leg of the 3ph vs. neutral, it's two legs of the 3ph - as I see on the top of the power poles in front of my neighbor's house.

At the top of the pole are three wires - 3ph at 4.6 KV. Two of those legs are tapped off and go to the transformer on the pole. Those two wires (no ground involved) can only be one phase. Obviously.

The secondary of the transformer (20:1 ratio, center tapped) provides 230V on the *two* wires coming to my house.

"Whenever you have a 2 wire source, there can only be one phase power obtained."

As you say. It's one phase to the transformer at 4600 volts, it's gotta be one one phase from that transformer. My service drop has two wires plus the carrier strand. That strand is connected to the center tap of the pole transformer which is grounded at the pole. Said strand is also grounded at my service entrance - two 8' ground rods separated by 10'.

(I'm not telling you anything you don't know, but there are lots of folks (here and abroad) who don't understand the point: just because you can center-tap a transformer doesn't mean you've generated two-phase. By extension, I could hook up a 1:1 transformer to both legs of my 230V and thereby get four-phase from these transformers' center taps. Does this actually mean anything? Don't think so...).

(Did I close parens correctly? Think so, but it gets tricky. :-)
)

-js

J Tiers
07-01-2019, 11:10 PM
Yes. Some call it two phase because there are two legs off the center-tapped transformer at the pole. Not right.

Small correction though, Jerry: it's not one leg of the 3ph vs. neutral, it's two legs of the 3ph - as I see on the top of the power poles in front of my neighbor's house.

At the top of the pole are three wires - 3ph at 4.6 KV. Two of those legs are tapped off and go to the transformer on the pole. Those two wires (no ground involved) can only be one phase. Obviously.

The secondary of the transformer (20:1 ratio, center tapped) provides 230V on the *two* wires coming to my house.
......
-js

Well, that does depend on the source and the type of transformer used by the utility.

Behind my house is a SINGLE line with a grounded neutral going to a butt coil or similar at every pole. Obviously there can BE only one phase on it.

Across the street is a 3 phase line, but even on that there appears to be a single line tap and neutral. I know this by observation of the wiring, and also by behavior. The line is through trees, and it is reasonably common for one phase wire to be damaged or have the fuse blow (three fuses are at the end of the block).

If one phase is out, then there will be six houses "on" and three "out". if two are out, then three "on" and six "out". Obviously if they were tapped between lines then there could be no case of just three "out".

We are drifting off the OP's subject, however.......

Noitoen
07-02-2019, 05:37 AM
Here in Portugal, aerial MT transformers are for town supplies are always connected to 3 phase 15Kv and the low voltage distribution on utility poles is done by a 5 conductor cable. One conductor is neutral (the Y connection of the transformer's secondary) connected to earth, one public street light wire and the 3 phase wires. They then supply the individual houses with one of the phase wires and a neutral. Local earth rod must be installed. Some houses, mine for example, are supplied with 3 phase and neutral 3x400v and 3x230v. Our utility meters are now of the "smart" kind that serve as a power limiter by switching off the supply. They also use power-line communication to read and remote control the meter.

Baz
07-02-2019, 08:46 AM
For a moment in post 11 it seemed Jerry was talking about the system I've seen in rural Australia of 25kv single wire, I mean single wire no return wire as that's what terra firma is for. Amazing that it works in such a dry country.
I work for a pan-European country so some of our test labs are wired to simulate 3 most common different standards of house wiring in our service countries. IT is about the only thing the Common Market never managed to unify - if they had we would be back on 50v DC.
One of our USA suppliers once admitted that when they tested power consumption of their product to meet Lot23 EU regulation it passed on one side of their lab but failed on the other side that was using a different phase.

plunger
07-02-2019, 09:09 AM
I dont know if a new thread should be started for this. The problem in S Africa is that there are very few motors that can run on 230v as well as 380v. Most motors over 2,2kw are all only 380v. I dont know if this is the same as Australia. In Normans manufacture link it shows some sort of transformer. Is this a step up transformer because they are normally very bulky and costly. More so than an entire vfd.
I dont get the center tap thing .?Also if you have single phase and spin a three phase motor ,does it create legs two and three.?Why do I keep hearing it creates the third leg. Where does the 2nd leg come from.
Also What magic determines a 380v motor compared to a 230v motor. Why would it care what voltage goes through it. ?Within limits of course.

Noitoen
07-02-2019, 10:09 AM
This thread has long been hijacked so here is a little more. For the same power, a 380v motor will draw less current than a 230v one. The difference lies in the construction of the winding. A 380v motor will have more windings of thinner wire than a 230v one. An extreme example can be seen on a engine's starter motor. For a few Kw of power, you need thick windings and cables compared to a higher voltage motor.

Single phase motors can be compared to 2 cylinder steam engines. To ensure a self start, there must be a crankshaft 90 out of phase. On the motor, you have the main and aux winding that's 90 out of phase and a capacitor that supplies the auxiliary winding also 90 out of phase.

Three phase comes in three independent waves phased 120. The steam engine equivalent would have 3 pistons and the crankshaft 120 apart. This configuration gives the best start ease.

PStechPaul
07-02-2019, 03:10 PM
In three phase, the vector sum of the voltages is zero at all phase angles, and the total power through the three wires is constant. This is one reason why a three phase motor runs more smoothly and quieter that a single phase version.

Jim Stewart
07-02-2019, 03:22 PM
I dont get the center tap thing .?Also if you have single phase and spin a three phase motor ,does it create legs two and three.?Why do I keep hearing it creates the third leg. Where does the 2nd leg come from.


Two separate things here. The center tap is used on single-phase 230V power in the US - its only purpose is to provide 115V as needed (most appliances and lighting in US residences is 115V).

Where does the 2nd leg come from? It's already there.
Let's say the single-phase power comes in on two wires, call them L1 and L2. Only two wires, so only one phase is possible.

If a third wire is powered by an RPC or VFD that wire gets the generated third phase. Let's say that third wire is called L3.

Then we have phase 1 on L1&L2, phase 2 on L2&L3 and phase 3 on L1 and L3.

-js

PStechPaul
07-02-2019, 05:38 PM
Here is a simple phase shifting circuit that produces three phase from single phase. The phase angles (118 and 122) are fairly close to ideal, but the voltages (221 and 125) are lower than that applied from the 254V line, and they collapse if a significant load is applied. However, it is difficult to model a three phase induction motor, which will supply its own back EMF once it is running. The voltages are 254 * cos(60) and 254 * sin(60).

http://enginuitysystems.com/pix/electronics/3_phase_static_converter.png

J Tiers
07-02-2019, 11:25 PM
......
I dont get the center tap thing .?

The US single phase voltage is 240V. The 240V winding has a tap at 120V (half the turns, or "the center"), which is made the neutral, so there are two "lines" and one neutral. if you want 120V, you hook from either line to neutral. If you want 240V you hook from line 1 to line 2.


Also if you have single phase and spin a three phase motor ,does it create legs two and three.?

Three phase has 3 lines. The "phases" are the voltage between lines in "delta" wiring. The single phase has 2 lines, call them "A" and "C". When you add the third line, which we can call "B", there are now three "phases", A-B, B-C, and the original C-A.


Why do I keep hearing it creates the third leg. Where does the 2nd leg come from.

See above. C-A is the original one phase, then adding the third wire gives you A-B and B-C.

The idler actually generates "back EMF", a voltage, as a normal part of running. For the "generated leg", the "back EMF" voltage is used as the output.... it is actually generated.


Also What magic determines a 380v motor compared to a 230v motor. Why would it care what voltage goes through it. ?Within limits of course.

The motor is wound with enough turns of wire per phase so that the iron will not saturate, which would cause it to draw a large current. for 380V it takes more turns of wire than for 240V. But it can be smaller wire, since the higher voltage is less current for same power.

To be economically priced, and compact, the motor is wound with the least amount of copper and iron. So it is "at maximum" when run at the high end of the normal voltage, 220-240V, 380-415V, 440-480V, 575V, or whatever the local voltage is. It needs to be reconnected, or re-wound to use a different voltage. What has to be done depends on what the "other" voltage is, vs the standard one.

Some motors are wound to take either..... 240V os the line-to-neutral voltage of a 415V three phase supply, so the 240V motor can run on 380 to 415V by wiring it "wye", or it can run on 240V line-to-line if wired delta.

Mcgyver
07-03-2019, 04:06 PM
Also if you have single phase and spin a three phase motor ,does it create legs two and three.?Why do I keep hearing it creates the third leg. Where does the 2nd leg come from.
.

I'm sure I'll hear about it if I'm wrong, but the sketch below might help - the leg is the pole or point, not the line connecting them. There's a signal between each point that has an AC voltage of whatever, say 220. Adding a 3rd point lets you have 3 signals, each 220V between them and each 120 degrees out of phase. Did a drawing for you that made it easier for me to get

https://i.imgur.com/PQnjsR0.jpg

Norman Bain
07-03-2019, 04:15 PM
To answer Jerry's question re "did it make a drumming sound on the shed walls?"

Answer is "not an amplification". The unit does have a vibration; they all do; hence there is a vibration if you put your hand on the cover and also a (I am going to say lesser) vibration if you put your hand on the wall at that location outside the shed.

To my feel the sound that used to be "down there next to the machine using it" is now "a hum that is way up over there" ... hence overall it is considerably less annoying than before.

J Tiers
07-03-2019, 04:38 PM
To answer Jerry's question re "did it make a drumming sound on the shed walls?"

Answer is "not an amplification". The unit does have a vibration; they all do; hence there is a vibration if you put your hand on the cover and also a (I am going to say lesser) vibration if you put your hand on the wall at that location outside the shed.

To my feel the sound that used to be "down there next to the machine using it" is now "a hum that is way up over there" ... hence overall it is considerably less annoying than before.

That is super, and I expect it is due to the good design of that RPC, they put the vibration damping inside the case. Once I saw that photo I decided it was not gonna be an issue.

It can be a "thing" though........I bought an RPC from a guy who had it up on a wall. When I first turned it on, it sounded like am old dump truck full of mixed hammers and sheet metal. Every piece of the case was loose, and the rotor was unbalanced. It must have been deafening up on the wall, it was bad enough on a concrete floor.

But it worked and the price was very good. I balanced the rotor, tightened the sheet metal, did NOT mount it on the wall, and set it on rubber feet. It just hums a bit now, enough to know it is on.