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3-phase isolation transformer in single phase application?

3-phase isolation transformer in single phase application?

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  #1  
Old 06-27-08, 10:39 PM
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3-phase isolation transformer in single phase application?

Here is a question you don't see every day . . . can I use a three-phase isolation transformer in a single-phase application?

First off, I am not an electrician, otherwise I would not need to ask this question! Eventually, I will hire an electrician to come in and help me with the installation.

I am going to have a separate circuit installed off my home's breaker box just for my audio system and home recording studio. The load on the circuit will never exceed 3kVA, even at peaks, and the average will be a lot less than that. (Inrush current for the isolation transformer itself may be a lot higher than 30A, but I'll install a slow-start device.)

The 1:1 isolation transformer will be installed between the breaker box and the equipment to be protected.

Normally I would simply use a single-phase transformer; however, I found a really beautifully built 12kVA 3-phase 1:1 isolation transformer being sold used at a VERY CHEAP price. I thought to myself, "Hmm, can I use that in a single-phase application?" I'm aware that the capacity would be 1/3 of 12kVA but that is more than enough for my needs.

Thing is, I'm not even sure if it can be done. You'd think you could Google something like this but Google brings up nothing.

Through Google I found links stating plainly that a 3-phase EMI/RFI filter can be used in a single-phase application. I found links stating plainly that a 3-phase line reactor can be used in a single-phase application. And I even got so far as locating a link stating plainly that a 3-phase transformer can be assembled from three identical single-phase transformers. BUT I couldn't find any link discussing whether a 3-phase isolation transformer can be used in a single-phase application.

If anyone knows the answer to this, please let me know! THANKS.

-- Chris
 
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Old 06-27-08, 11:16 PM
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Genreally the answer is no

the reason why i say no because the way the transfomer can be hook up in delta or wye format so hard to tell if it can be done in safe manner or not.

I will let other guys chime in with auido system they have somehow more knowage than I do they will expain few details here.

Merci,Marc
 
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Old 06-28-08, 06:21 AM
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na i'm afraid not, hope you didn't pay to much for it . i've been trying to run it through my head, just can figure out how you'd do it.
 
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Old 06-28-08, 06:37 AM
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Even if you were to get it to work, I suspect the efficiency wouldn't be all that great. In addition, it may not actually be 1:1 when the smoke settled. I think I'm with the other opinions here, it's not a good fit for your application.
 
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Old 06-28-08, 07:49 AM
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I don't see why it wouldn't work

First off: i've never tried it. So, I can't be sure.

However, if you energize only one of the primaries, the corresponding secondary should see a 1:1 voltage.
The comment about lower efficiency has merit, since you are creating magnetic flux thruout the entire core, where you only need to energize the 1 phase.
The 2 other primaries and 2 other secondaries should, of course, be treated as HOT (they will be) and suitable isolated.
I'm going to also suppose that all windings are available in the 3phase transformer, so you do have access to both leads for all windings.

So, how does this help your audio room? Hum mitigation? Are you going to leave the secondary ungrounded?
 
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Old 06-28-08, 11:25 AM
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Originally Posted by telecom guy View Post
if you energize only one of the primaries, the corresponding secondary should see a 1:1 voltage.
The comment about lower efficiency has merit, since you are creating magnetic flux thruout the entire core, where you only need to energize the 1 phase.
This is the main problem that I see also. I can't think of any good way of predetermining just how much energy is wasted other than hooking it up and measuring realtime with clamp meters.
 
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Old 06-28-08, 11:50 AM
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another thought, if he did just hook up one primary winding, wouldn't the load from trying to energize the other 5 other coils (two primary, 3 secondary) be extremely high? Even if it were unloaded? Just a thought.
 
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Old 06-28-08, 12:07 PM
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Originally Posted by nova_gh View Post
another thought, if he did just hook up one primary winding, wouldn't the load from trying to energize the other 5 other coils (two primary, 3 secondary) be extremely high? Even if it were unloaded? Just a thought.
Nope. An open winding won't add to the load, though the size of the transformer will affect efficiency as I previously mentioned.
 
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Old 06-28-08, 01:02 PM
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Let me step in here a bit now I can see where it is going but however with 3 ph isolated transformer It can be done but i will NOT recomeoned at all due serveral reason

You will not get full rating of the transfomer

You will still have to do the bonding and grounding this part you can NOT isolated at all { this is very specfic in the NEC }

The 3 phase isolated transfomer will come in both wye or delta verison wye side is not bad but delta side now that will be tricky and myself i personally will not encourged to use this transfomer for AV system there is a correct single phase tranfomer out there to do the task correct.

Now if you ran the AV cables keep them away from power line at least a foot or more that way it will reduce the amout of the " noise " in the system.

Merci,Marc
 
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Old 06-29-08, 09:40 AM
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I'm not sure what your primary voltage is or the secondary voltage you're trying to obtain however, let's say you feed your 3 ph transformer 240 volt 1ph and you're looking to get 120 volt on the secondary. What you're going to see is 120 volts on one secondary phase and 1/2 the voltage on the other 2. If you feed a transformer 3 phase then you can get single phase off it, single phase primary not going to work.
 
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