19 replies to this topic

[RallyRed]

Certainly not a new idea, but just for those who want to run a compressor, hoist , whatever from poor mans power, as it often comes up in threads.

 

http://get3phase.com.au/

 

 

[yel327]

Even these guys get the terminology wrong! They talk about 415V 2 phase supply, you never get that, only 240V single phase, 415V single phase or 415V 3 phase. You may get two phases plus neutral into you house but connecting across two phases is a single phase supply or you get 2 x 240V single phase supplies.
Great idea

[RallyRed]

yep....used to get pulled up by the old tradies when I was an apprentice.....""it's single phase 415...dont call it 2 phase!!""

[CYCO355]

Even these guys get the terminology wrong! They talk about 415V 2 phase supply, you never get that, only 240V single phase, 415V single phase or 415V 3 phase. You may get two phases plus neutral into you house but connecting across two phases is a single phase supply or you get 2 x 240V single phase supplies.
Great idea

I work in the electrical distribution network here in WA and we supply 3 types - single phase 240v three phase 415v and two/split phase 500v. When we put up a single phase transformer we can set it up as either single phase or two phase and when we do our checks we would expect to get around 480v when we check phase to phase on a 2 phase set up. I've seen one with a tad over 500v in my short liney career.

[yel327]

What transformer connections are you using for a 2 phase supply off a single transformer? I'm not getting how you can get 480-500V across 2 x phases unless you are using 2 x single phase transformers or a Scott-T TXF connection. I've never seen anything like that over here on a domestic supply although 2 phase generation used to exist many years ago, possibly not local to me though. I remember reading that Niagara Falls used to be 2 phase generation.

[CYCO355]

I tried to google the transformers we use but there not showing up, I'm on a RDO today but tomorrow I'll see what I can find on our computers if not I'll take a few pictures for you.

[CYCO355]

I'm 6 months off finishing my apprenticeship so I thought I'll go up the shed and check the paperwork I've got here.

[axistr]

I am not an electrician but to get true three phase power supply the phases need to be 120 degrees apart or you can damage the equipment, its not just the high voltage due to the wiring in series you need..

[RallyRed]

Can say I've seen that sort of connection before Cameron...but as you do it, it must be so, and work well. 

 

However, the drawing seems to show that its just a Single phase HV side, and a single phase LV side, just that there are 2 seperate windings on the LV side.

I'm assuming the 2 LV windings are the same phase ( i.e.no actual phase difference between them, no offset type winding), as it refers to them being possibly being wired in parallel,.... and wiring things in parallel that are not in phase is not a good look, also noisey, smelly, hot and scarey. 

 

Interesting info though.

Edited by RallyRed, 03 January 2017 - 06:24 PM.

[CYCO355]

The two LV windings is were you get the two different phases and when wired in parallel you'll just have a single phase (240v) coming off the transformer.

[Statler]

So do i need to buy a single phase motor for my hoist (to replace the 3 phase) or not?

[yel327]

So do i need to buy a single phase motor for my hoist (to replace the 3 phase) or not?

 

No, this device that this thread is about will do the job for you. You may have to connect the 3phase motor in Delta though so it becomes a 3 phase 240V motor. Most small 415V motors are connected in Star but if reconfigured (easy to do) they become a 240V 3phase motor. It is not a new concept, you can buy Variable Speed Drives (VVVF) that are 240Vac single phase input and convert the output to 240Vac 3phase, this item is probably simply that - just a device with a 240V single phase converter at the front end, chops the power to DC and a 3 phase inverter hanging off the back end, fed by the DC output of the converter. In the end though for a one off application it is probably easier to buy the single phase motor. If you might have a use for 415V supply in the future for other purposes it might be worth the expense.
 

[RallyRed]

The two LV windings is were you get the two different phases and when wired in parallel you'll just have a single phase (240v) coming off the transformer.

yep...we are saying the same thing. It;s just the terminoligy of "phase".

 I dont believe they are actually 2 phases. They are just duplicate windings of the same phase. Thats why they can be connected in series or parallel.

 

 I could be wrong.

[yel327]

I'm 6 months off finishing my apprenticeship so I thought I'll go up the shed and check the paperwork I've got here.

 

It is a common Single Wire Earth Return (SWER). It is just a HV (probably 22kV) to 480V single phase transformer with centre tap. it is the same principle as supplying two phases and neutral to a customer, they get either 240V single phase or 415V single phase, but in that case they only get 415V as the phases are 120deg apart (240V x root3). In this case the two windings are most likely in phase, and are as Col says effectively simply 2 x single phase transformers sharing a common HV winding (or a 480V winding with centre tap, same same), hence the phase to phase measurement is not sqrt3 x 240 (=415V) but 2 x 240V = 480V. The end result is if the customer took both supplies plus neutral would be two 240V single phase supplies (Active 1 to Neutral and Active 2 to neutral) plus a 480V single phase supply (Active 1 to Active 2). In rural areas with large impedance drop in the overhead lines, having 480V available for larger motors or for welding means you use half the current.

 

However the device that is the subject of this thread if connected to the 480V supply would still be connected single phase 480V, not 2 phase as stated on their website! 
 

Edited by yel327, 03 January 2017 - 07:32 PM.

[mick_in_oz]

For your hoist, you have two options, a new single phase motor, or a VFD (Variable Frequency Drive) to convert your current single phase to 3 phase to run the motor, truth be known the price either way will likely be similar, maybe a lil cheaper to go a new motor.

 

As for the above transformer pic, its single phase input, it can only be single phase out, regardless of the number of secondary windings it has, all of the secondaries will be in phase with one another and there is no way there can be the 120deg difference between them.

[yel327]

There is a 3rd option Mick, one of the devices in this thread. To go 240V 1ph to 415V 3ph it must have a 240/415V single phase transformer up front - they say they can do this, so no need to reconfigure the 3ph motor to delta connection which is what is needed if using a VS drive alone.
As I said though unless you plan to use it for other 3ph applications a new 1ph motor will be easier and cheaper

[CYCO355]

As for the above transformer pic, its single phase input, it can only be single phase out, regardless of the number of secondary windings it has, all of the secondaries will be in phase with one another and there is no way there can be the 120deg difference between them.[/quote]
It is a single phase transformer but when wired for two phases you get two seperate phases with 240v, when you test between them you get 480v, if they were the same phase you'd get 0v when tested.

[yel327]

Think again! Think of it as a 480V single phase secondary with a centre tap. These are common in mines but 240V with centre tap. They are not separate "phases" if they are in phase, and if the actives are not in phase you won't get 2 x 240V, you only get 480 V as they are in phase with each other.

Edited by yel327, 03 January 2017 - 08:34 PM.

[RallyRed]

no wonder they had to cancel the Phase 4...its hard enough to understand 3 phases, let alone 4!!...lol

 

Like I said...the confusion here ( if there is any) is related to the term ""phase""....that transformer only has 1.

From a supply authority type view, it may be said that different consumers are on different phases ( 3 phase transformer) to spread the load across the transformer's capacity.

Likewise, from a supply authority type view, the transformer above, may have 2 different consumers connected to the secondary LV windings . 1 consumer per winding for example. 

This may be generically said to ""have 1 consumer/load on each phase"", as this is somewhat similar to the 3 phase txf mentioned above.

However...in this case they are not phases, just windings.

IMHO