Single Phase 230V supply and 3ph Compressor install.

[Simon47]

Thanks for that, you bring back memories (not all good ) of trying to get my head around some of the theory when I was at uni (back in the early 80s when this sort of stuff was becoming obsolete for new designs). Not a lot of it stuck, other than the principle of the Ward Leonard system. I could just about get my head around the Amplidyne , but the Metadyne was another thing altogether - dad once tried to explain it to me, but it was just too much and nothing sunk in. IIRC teaching on the theory of these machines went barely any further than "they exist but they're just about obsolete now".
I do recall that if sat in the library at the top of the engineering labs, you could hear the MG set spin up when someone called for the lift - and it would spin down again after a few minutes of inactivity. The lift could go unused for significant periods because we had that great invention - the Paternoster.

BTW - why do you say the wound rotor rotary converter is not usually be AC-AC ? I'd have thought that they'd be ideal for the application under discussion - with a controlled rotor field giving a much better synthesis of the third phase. I'd perhaps have considered playing with one, but it's not the sort of machine you tend to see lying around in scrapyards - and I don't have the time to go wandering around them like my dad did (on first name terms with the owners , there's a reason mum named the house "Magpies Nest").

 

[Lucien Nunes]

I'm not familiar with the synchronous rotary being used for phase conversion although presumably they were at times. I should find out why, but top of head I dont think they offer enough advantage to offset their extra cost and complexity. The armature winding would be under-utilised, the unconverted power advantage is lost, it still can't entirely fix the symmetry as an M-G set does. My impression is that if perfect output is needed one must use an M-G, otherwise one might as well use an induction machine. The efficiency of a synchronous type really comes into its own with 6-phase on the AC side as the fraction of power that needs conversion is further reduced, the remainder flowing straight through as in a synchronous commutating rectifier.

FWIW we still have one machine in daily use with a Ward-Leonard drive, incorporating a Rosenberg / Metadyne type servo-amplifier in the control circuit. See:
1950's DC spindle drive still hard at work in 2020

 

[itstony]

I'm not familiar with the synchronous rotary being used for phase conversion although presumably they were at times. I should find out why, but top of head I dont think they offer enough advantage to offset their extra cost and complexity. The armature winding would be under-utilised, the unconverted power advantage is lost, it still can't entirely fix the symmetry as an M-G set does. My impression is that if perfect output is needed one must use an M-G, otherwise one might as well use an induction machine. The efficiency of a synchronous type really comes into its own with 6-phase on the AC side as the fraction of power that needs conversion is further reduced, the remainder flowing straight through as in a synchronous commutating rectifier.

FWIW we still have one machine in daily use with a Ward-Leonard drive, incorporating a Rosenberg / Metadyne type servo-amplifier in the control circuit. See:
1950's DC spindle drive still hard at work in 2020

Thanks for the last couple of additions, that was quite interesting. I am sure others viewing will have too. To rare forum thread goes that extra bit extra on a topic.

I hoped for a couple of recommendations an a good value VFD control, but that is always dependent on that person deciding to check the forum. I will buy a good value, will not buy based on cheap. Apologies if I already wrote that. Never buy cheap, only good value.
Looking like the Invertek is in pole position. They are good gear, just the cost I must decide on.
Thanks to all on all the input ?

 

[cliffed]

Maybe reading this wrong but can’t you connect delta using the single phase supply.

 

[Simon47]

If you look back, that's something I mentioned a few posts ago. But it's not as simple as just connecting two terminals to the supply - all that would do is make the motor hum for a few seconds until the supply fuse/breaker trips. For the motor to start, it needs a rotating magnetic field, which is normally provided (for a 3 phase system) by the three phases being offset by 120˚from each other.
For a single phase motor (excluding small ones like series wound and shaded pole), it will have a second winding fed via a capacitor - the capacitor providing a phase shift so that the two windings (the main one being connected directly to the supply) have magnetic fields that are out of phase. The starting winding can either be permanently connected, or just used for starting (via a centrifugal switch), or sometimes a combination with a smaller cap for running and a larger one switched in for starting.
What you can do, subject to some limitations, is use a 3P motor wired delta, and connect a capacitor between one of the supply lines and the third terminal. This will provide a phase shift and allow the motor to start. Once running, the capacitor helps to balance the phases. More capacitance is likely to be needed for starting - and the Transwave converter I have in the garage has a voltage sensitive relay to switch extra caps in when it detects the effects of starting a motor on it.
In practice, the starting characteristics are not likely to be suitable for a compressor - it just won't have the torque unless you can completely unload it until it's up to speed.
And I suspect you need to derate the motor (i.e. fit a bigger one than the load would normally need) because you are loading one winding considerably more than the others, and I suspect there will be higher currents in the squirrel cage (and hence more rotor heating) as a result of the imbalanced winding currents.

 

[itstony]

If you look back, that's something I mentioned a few posts ago. But it's not as simple as just connecting two terminals to the supply - all that would do is make the motor hum for a few seconds until the supply fuse/breaker trips. For the motor to start, it needs a rotating magnetic field, which is normally provided (for a 3 phase system) by the three phases being offset by 120˚from each other.
For a single phase motor (excluding small ones like series wound and shaded pole), it will have a second winding fed via a capacitor - the capacitor providing a phase shift so that the two windings (the main one being connected directly to the supply) have magnetic fields that are out of phase. The starting winding can either be permanently connected, or just used for starting (via a centrifugal switch), or sometimes a combination with a smaller cap for running and a larger one switched in for starting.
What you can do, subject to some limitations, is use a 3P motor wired delta, and connect a capacitor between one of the supply lines and the third terminal. This will provide a phase shift and allow the motor to start. Once running, the capacitor helps to balance the phases. More capacitance is likely to be needed for starting - and the Transwave converter I have in the garage has a voltage sensitive relay to switch extra caps in when it detects the effects of starting a motor on it.
In practice, the starting characteristics are not likely to be suitable for a compressor - it just won't have the torque unless you can completely unload it until it's up to speed.
And I suspect you need to derate the motor (i.e. fit a bigger one than the load would normally need) because you are loading one winding considerably more than the others, and I suspect there will be higher currents in the squirrel cage (and hence more rotor heating) as a result of the imbalanced winding currents.

I have ventured down that road too of capcitors and for the reasons made above is why it was deemed a no go. If it was that easy, sure it would have become a common knowledged theory years ago.
The VFD route was chosen and the call made to discuss more on the selection I had a different Tech lad this time and a.very different view.
His line was he hears this question all the time and does not suggest a VFD and why. That it may provide the mans to work, but other factors such as Other controls etc it may have may be 380v rated and will be seeing 230v and not compatible with the reduced 230volts, so look deeper on this area.
The suggestion was the Rotary converter as that would be the Recommended way forward.
Be great if there were other 3P items to run, there isn’t, so £900+/- is not going to fly.
Be nice to locate a second hand one, but not seen any even though I bet there are many On walls unused.
Thanks for all the replies and learned a lot more than I knew.

 

[Simon47]

I have ventured down that road too of capcitors and for the reasons made above is why it was deemed a no go. If it was that easy, sure it would have become a common knowledged theory years ago.

It's a well known technique. But as you've found, it's non trivial and you need a box of caps so you try different values till you get the best running for you're specific needs.
The commercial unit I have has a 6 way switch for different cap values.

 

[itstony]

It's a well known technique. But as you've found, it's non trivial and you need a box of caps so you try different values till you get the best running for you're specific needs.
The commercial unit I have has a 6 way switch for different cap values.

Did you build it?
The rotary converter ticks all boxes with 3p out, just the unjustifiable for my stuation.

 

[Simon47]

The commercial unit is one that was being scrapped from work and the maintenance manager scrapped it my way Dad had it set up in the garage to run his shaper - the lathes he ran from a VSD, and everything else was single phase. TBH I have no idea how it would fare starting a high-inertia load like a compressor - on the shaping machine it would only be starting the (fairly small) motor with the clutch disengaged. At the moment it's in storage like a lot of other stuff waiting till I can get my own garage built.
I had been experimenting with building a roatary convertor to get 3P in my mates garage - primarily to run the lift. I got as far as having a lash-up with something like a 5hp motor, a large step up transformer, and old fashioned manual star-delta starter, and some caps. But them my mate got divorced, the house was sold, and I never got any further. The plan there was to use the large motor as an induction generator to balance the phases so as not to be so reliant on the caps. To a large extent I was following guidance from dad - he knew "quite a lot" about electrical machines, having designed them for Brush many years ago.