ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
ShoutChat
Recent Posts
UL 508A SPACING
by ale348 - 03/29/24 01:09 AM
Increasing demand factors in residential
by tortuga - 03/28/24 05:57 PM
Portable generator question
by Steve Miller - 03/19/24 08:50 PM
Do we need grounding?
by NORCAL - 03/19/24 05:11 PM
240V only in a home and NEC?
by dsk - 03/19/24 06:33 AM
New in the Gallery:
This is a new one
This is a new one
by timmp, September 24
Few pics I found
Few pics I found
by timmp, August 15
Who's Online Now
1 members (ale348), 302 guests, and 14 robots.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
#129836 09/19/05 01:22 AM
Joined: Jun 2004
Posts: 176
P
Member
I am trying to understand 3 phase a little bit better. I was wondering, is there such a thing as a transformer with a single phase input, and three phase output? Is it possible to make one? (I'm not talking about phase converters that use electronics or a motor/genset combo, i'm just talking transformer here)

Stay up to Code with the Latest NEC:


>> 2023 NEC & Related Reference & Exam Prep
2023 NEC & Related Reference & Study Guides

Pass Your Exam the FIRST TIME with the Latest NEC & Exam Prep

>> 2020 NEC & Related Reference & Study Guides
 

Joined: Sep 2003
Posts: 650
W
Member
If you are strict about the system being a pure transformer, then you cannot build a single to three phase transformer. This is because you need some sort of phase shift somewhere to produce the necessary phasing difference.

The simplest single to three phase converter is an induction motor. Note a motor/generator combo, but just a single motor. You supply single phase power between two of the terminals, and extract your third leg from the other terminal. The single phase supply stores energy in the rotation of the rotor, and you get that back (with pretty good phase shift) from the other terminal. This is probably the closest thing to meet the description of a single to three phase transformer.

Once you have at least two phases, you can use transformers to combine the two phases in appropriate proportions to get any other phase count. Apparently three phase to 12 or 18 phase transformer sets were (are???) sometimes used to feed power to rectifier banks to produce DC with very low ripple.

-Jon

Joined: Jun 2004
Posts: 1,273
T
Member
Google rotary converters.

Static phase converters will be found, also.
http://www.homemetalshopclub.org/projects/phconv/phconv.html
http://home.att.net/~waterfront-woods/Articles/phaseconverter.htm

If you are willing to tinker, you can build your own rotary converter inexpensively.


Tesla
Joined: Oct 2000
Posts: 2,723
Likes: 1
Broom Pusher and
Member
I like Winnie's descriptions using an Induction Motor.
May sound strange to some, but the Induction Motor is a Transformer with a "Spinning Secondary", and as pointed out by Winnie, the Aux. Winding of a 1Ø Induction Motor may be used to create a Polyphase output from a Single Phase input (by incorporating the Aux. Winding's lead with the 2 leads of the A.C. Power System).

As Mr. Spock would say: Fascinating!!!

Scott35


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Joined: Jun 2004
Posts: 176
P
Member
Thanks for the help. For some reason, I thought that if you could rotate a secondary out of phase, it would lead or lag, Instead, i hit me that it would decrease the amplitude...

Vout=Vsec*cosθ, where θ is the relative angle that you rotate the secondary.

The only way it would be possible without using moving parts would be to use 2 pieces of ferromagnetic material which are timed correctly behind and forward in the space-time continuum... or something like that

Joined: Sep 2003
Posts: 650
W
Member
That technique works pretty well to change from N phases to M phases, where N is greater than 1.

You simply use a wound rotor motor, with the stator wound for N phases, and the rotor wound for M phases, and lock the rotor in position.

In one of my worksites, we used a wound rotor induction machine, which looks exactly like the transformer that you describe, with a three phase primary and a three phase secondary. The rotor was anchored to a gear box that let us rotate it, but would hold it in whatever position it was placed. By changing the rotor position we would change the phase of the voltage induced in the rotor coils. The rotor coils were connected 'buck/boost' to the feed lines, giving us a nice variable voltage three phase output.

-Jon

Joined: Jun 2004
Posts: 1,273
T
Member
May sound strange to some, but the Induction Motor is a Transformer with a "Spinning Secondary", and as pointed out by Winnie, the Aux. Winding of a 1Ø Induction Motor may be used to create a Polyphase output from a Single Phase input (by incorporating the Aux. Winding's lead with the 2 leads of the A.C. Power System).
Scott35

To get the correct phase angle you’ll need a 3 phase induction motor as your ‘idler’ or rotary converter….

It does not need to be large. Typically a 2hp idler can support 7.5hp loads.

Visit my prior links.


Tesla

Link Copied to Clipboard
Powered by UBB.threads™ PHP Forum Software 7.7.5