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#128292 - 01/13/03 09:25 PM Phase converters  
Steve T  Offline
Member
Joined: Feb 2001
Posts: 306
Oak Park, IL, USA
Can someone please give a quick description of how a converter works?

Any good books on converters?

I saw a basic diagram of a converter but didn't understand how the single-phase line became 120 degrees apart.


Tools for Electricians:

#128293 - 01/13/03 10:52 PM Re: Phase converters  
Bjarney  Offline
Moderator
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
Although they make commercial products, there’s some interesting info at sites like www.gwm4-3phase.com and www.phaseconverter.com

From a D-I-Y vantage point, usenet newsgroups rec.crafts.metalworking and rec.woodworking address the subject periodically in motor FAQs.

Because the output of virtually all converters is 3-wire, there is no wyepoint neutral to connect to or measure, so no 120°-wye service. They are closer to a 240V Δ system, or maybe 240/120V 3ø 4-wire open-Δ. This gives you the “original” 240V—L1 and L2, and a second approximately 240V that is shifted by roughly 60° for L1-L3; giving around 240V for L3-L1. Don’t expect very tight voltage balance—that is generally implied when reading converter-manufacturer literature.

Because converter phase-to-phase voltage can be fairly unbalanced, so significant motor-horsepower derating [about 57% in some cases] may be necessary. Rotary phase converters have to be started and up to speed before running any connected 3ø motors. Don’t plan on powering any controls from the phase converter—they are not generally stable/regulated enough for that.

Don’t forget NEC ARTICLE 455.


#128294 - 01/14/03 02:48 AM Re: Phase converters  
Scott35  Offline

Broom Pusher and
Member
Joined: Oct 2000
Posts: 2,707
Anaheim, CA. USA
In a nutshell, it's like a UPS with 3 Phase output (per "Static" Converters).
The 1 Phase AC may simply have a 3rd line created, or the entire AC is converted to a 3 Ø system.
Either way, AC is converted to DC, which is then Inverted to AC.

If this was a Rotary Converter, it would be a 1 Phase Motor driving a 3 Phase Genny (Generator).

Better explainations may be done by others, or if I get proper data, I'll post it.

Scott s.e.t.

p.s. pay no attention to the following text. Just trying out some extended characters.

¡ ¢ £ § © ª « ¬ ­ ® ¯ ° ± ² ³ µ · ¹ º » ¼ ½ ¾ ¿ × Ø ø


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

#128295 - 01/15/03 08:28 AM Re: Phase converters  
Gwz  Offline
Member
Joined: Apr 2002
Posts: 197
On those extended characters which combination of keys produce the ' ohms ' symbol and the ' square root ' sysmbol ?


#128296 - 01/15/03 01:53 PM Re: Phase converters  
Scott35  Offline

Broom Pusher and
Member
Joined: Oct 2000
Posts: 2,707
Anaheim, CA. USA
Gwz,

Not sure myself what the keystrokes are for these symbols (Omega and Square Root).

They are simple ones with True type Fonts - Omega = W in the Greekx Fonts, Square Root = alt+0214 in the Symbol Fonts.

If anyone knows what the keystrokes are for these two symbols - using the plain Courier Font, please let us know ASAP!!!
(not a True Type, Postscript, or SHX Font - just an ASCII basic Font)

TIA!!! [Linked Image] [Linked Image] [Linked Image]

Scott35 s.e.t.


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

#128297 - 01/15/03 06:23 PM Re: Phase converters  
Bjarney  Offline
Moderator
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
"alt-251" (not 0251) gives the root symbol, ã but it does not translate correctly to e-c.net posts.




[This message has been edited by Bjarney (edited 01-15-2003).]


#128298 - 01/15/03 06:32 PM Re: Phase converters  
Bjarney  Offline
Moderator
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
"alt-234" is {omega} from http://www.asciitable.com but it does not translate correctly in e-c.net posts.

Some call this chart 'code page 437' but not sure exactly why. http://www.nefec.org/UPM/sibmext.htm




[This message has been edited by Bjarney (edited 01-15-2003).]


#128299 - 01/25/03 11:39 AM Re: Phase converters  
Steve T  Offline
Member
Joined: Feb 2001
Posts: 306
Oak Park, IL, USA
I am not going to do any projects myself, except inspect the installation of a rotary converter.

The diagram at www.gwm4-3phase.com/rotconn.gif is how the one I saw appeared to be hooked up (except for them using an extension cord and not having some FMC installed correctly).

This being my first time dealing with a phase converter, I had imagined two wires going in one side, and three wires coming out the other side. This is not the case.

The diagram, in essence, shows two wires going in and ONE wire coming out.

Or is this a case of single phase feeding thru two wires 180 degrees apart, L1, L2, with three phase coming out thru the same wires L1, L2 120 degrees apart and a third line, L3 being created?

Is it possible to have single-phase and three-phase current on the same wires at the same time?


#128300 - 01/25/03 11:24 PM Re: Phase converters  
Scott35  Offline

Broom Pusher and
Member
Joined: Oct 2000
Posts: 2,707
Anaheim, CA. USA
Steve,

The method used in your explaination and on the converter shown on linked image is typical of the first type I mentioned in the first reply (creates a 3rd line).

The Motor(s) and the Converter will be connected to the 1 Phase power system, across the Ungrounded Conductors (or L-L).
The Converter creates a circuit which has a Potential Difference between the newly created "Phase Line", and both of the existing 1 Phase Ungrounded Conductors.

The offset is probably in the range of 60º or so, which will be sufficent to create a Rotating Magnetic Field within the Motor.

This is the simplest method of creating Polyphase from Single Phase, but it is also the "Crudest".

Scott35 S.E.T.


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

#128301 - 01/25/03 11:40 PM Re: Phase converters  
Bjarney  Offline
Moderator
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
Steve, instead of visualizing it as a wye case, consider it more like a 4-wire-delta arrangement. There will still be ~240V between L1-L2 [and about ~120V L1-N and L2-N.] For the “manufactured” T3, there will be ROUGHLY 240V L1-T3, T3-L2 and ROUGHLY 208V T3-N, but don’t expect nice, even, symmetrical measurements like you’d see with conventional utility-type delta transformer service.

Also, don’t plan to power controls or other 1ø devices from T3 and any other lead. Voltage stability will be marginal (and likely disappointing) at best.




[This message has been edited by Bjarney (edited 01-25-2003).]


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