Three-Phase to Single-Phase Transformer

Hello shekhar28280

You can do this quite cheaply, by using a Single Phase transformer with a 440 Volt Primary winding, connected across two of the 3 available Supply phases.

The Secondary winding of that above Single Phase Transformer to be whatever Voltage you require.

You should not require a connection diagram for the above, if you intend doing the work.

The Scott-T transformer is a much more costly but elegant way of ensuring the load on the Primary 3-Phase supply mains is equal, and can supply two entirely separate phases as outputs, but those phases are not able to be connected in parallel.

Read more about the Scott-T transformer (enjoy the connection diagrams ) here: http://en.wikipedia.org/wiki/Scott-T_transformer

Kind Regards....

Regards

Your answer is the best of lot, as I remember of having Control-Tranformers in Siemens Eqpt having 220V & 380V [to which we normally call 440V] for dual i/p connectionc provision.

Regards

Let's take this situation :

Source: 480V/3P , Load: 208V/1P , 30kW , FLA = 144A . Is the option of using a Scott T the best solution ? So that from a 480V/3P source, it will see a balanced load . Namely, 36.1A ? [Phase A - B - C ]

Thank you.

Hello, Mr. Shekhar,

We have an inexpensive alternate of Scott-T transformer, which I had already supplied in past, Please write on my email with full details, and qty required,

Regards

Rakesh Semwal

Chandrashekhar,

"I want to use 3 phase to 1 phase transformer in railway application to supply auxillary load up to 10kvA.I have 3 phase 440V input supply & want to use as primary voltage of transformer."

Your email is not quite clear.

I understand you have 440 V 3-phase power available to power the transformer.

Do you have an existing transformer now available to you or do you intend to buy one?If you are buying one , why not specify exactly what you want to your supplier.

If you have an existing one, I can tell you how to modify it to get the single phase supply you need.You need to tell me what secondary phase voltage you want to use.

If you had a 3-phase or 3 single phase transformers already, you can use a modified "zig-zag" connection.

We do it all the time on 3 phase Diesel gensets .

I look forward to your reply

Hello again shekhar28280

Is your 3-phase 440 V Supply from a small diesel or similar generator set alternator?

Do you require the 3-phase supply to be balanced across the 3 phases?

The load of 10kVA is not large, if spread across 2 supply phases.

If you don't worry about a small imbalance on the supply phases, use a single-phase transformer.

Your supply voltage is 3 phase 440V you say.

So you need a single phase transformer with a primary of 440 V and a secondary of 220 V.

These transformers are very common, as power network or distribution transformers.

If you are intending that the 3-phase supply be balanced, as I said earlier http://cr4.globalspec.com/comment/287454/Re-3-Phase-to-1-phase-transformer then you are going to have an extremely expensive and complex system to obtain the 220 V single phase output from a 3-phase 440 V input.

If you did not understand my earlier Post, or this one, then please do not attempt anything electrical.

Instead obtain the services of a qualified electrician, who should know immediately what to do.

Reply here, with

kind Regards....

I understand what poster need is a transformer that can give an output of 220Volts 50hz with the 10KVA load,

Input has to be supplied from a 3pahse 440Volts system in delta or star connections, and must have a balanced current in all three phases,

Its not a scott T transformer,

We are alraedy making this product with no electronics,

Regards

Hello rakesh_semwal

Please send me details, including connection diagram, what size/s you make, and other details, in a Private Message at

Kind Regards....

Hello Sparkstation,

Its a device not a single transformer but without any electronics. contained in sheet metal box, 3 or 4 input wires depending on requirements of delta or star connections and 2 Output wires Earth terminal provided.100% exact conversion of input wave shape.balanced input current.Its simple as any electrical equipment should be. Right now we are making up to 35KVA Output. but if required can be increased,

Hello rakesh_semwal

Could you send me details per my earlier request, thank you: http://cr4.globalspec.com/thread/27383#comment288334

I am not intending to manufacture the item.

Kind Regards....

Hello sparkstation

See the below circuit.technically explained my previous post,

Hello again, rakesh_semwal

I can see your diagram, and it will work, delivering 1-phase output for 3-phase balanced input, as you say.

The system efficiency is not as great as a single transformer, because at various times of each of the the 3 input phases, some of the single-phase secondary transformer windings are just resistance/reactance in the single phase circuit, while not actually being energised, and thus waste energy.

As for me, I would tend to use the cheaper single phase transformer, as explained in my first Post above, mind you, that loads 2-phases of a 3-phase supply.

Kind Regards....

Not a big difference in system efficiency even Scott-t Transformers have this level of loses,and you need two load to run them at full efficiency,but only disadvantage is that its 1.7 Timers larger then a single transformer, as you are taking only 3.33KVA from a 5.8KVA rated transformers,But yet again scoot-T Transformers are also large in almost same proportion.

So it can replace a Scott-T transformer with out needing two equivalent loads. and at half of the cost, as scott- t are very expensive.

Two phase transformers are not going to give you a balanced input current,thats going to put much more inefficiency in the system,

Well its seems good for 1 phase supply only.

I have three phase primary input .So provide me 3 to 1phase convesion transformer diagram.

Its for 3 phase input supply, You can see X, Y and Z phases indicated in drawing.

Can I do this with 480Volt, 3 phase on the Primary side of the Transformer without a neutral ? I don't believe they ran a Neutral to the Panel Board from the Load Center Breaker Feed.

I need to go from 480 Volt, 3 phase 90 amp spare Breaker and make a single Phase, 208 Volt - 180 Amp source for a Furnace System ( 37.5 KVA ).

From your Ckt Diag, Can it be done this way ?

I want to keep a balance system within the Panel board.

Thanks

L

hi

is this circuit correctly work?

you test it?

Null point out Y connection should be Earth?

What power this circuit can be used?

wrong secondary connection

I love the diagram,,,,,,,

But, please, permit me to ask, can I have the transformer windings in a single transformer?

I mean, instead of having 3 transformers of the same winding, would it be proper to have the three done on a single transformer?

Please, the advantages and the disadvantages?

Rakeash, If what you say is correct , I know exactly what he needs to do to mofify three single phase 33 KVA transformer s to achieve this voltage.

It will involve getting his hands wet wil oil but , he will get 3-phase balanced load on the primary and 240 V single phase secondary voltage.

Regards!

I remember in 1950s when Power-lines & Supply conditions were poor in Pakistan X-Ray units had such 3Ph to single-ph transformers, but they werewere using 2phs connected to 11kv & out-put connected in series to get 220V at a better condition.

Hello, shekhar, sparkstaion and jecob,

As shekahr don't seams to be interested in buying it from us, I m going to shear information here,

You just need to make 3 single phase transformers of 5.8KVA with the output voltage of 127 Volts and can be operated at 230Volts AC,

so you have 6input wires, Tie one inputs wire from each transformer together and make it a common point for neutral wire where as remaining 3 input wires can be connected to three phases X Y and Z,

Now you can connect all three inputs of three transformers in series like three batteries, and its going to give you an output of 220 volts,

Heres is some calculation.

Required output 10KVA

OUT CURRENT =10000/220=45.5 Amps

Since phase angle is 120Deg Voltage of each transformer=220/1.73=127

IF Connected in series total output voltage =(127+127+127) /1.73=220volts.

KVA Rating of each transformer=127x45.5=5.778KVA

Please note to get the right results output of each transformers has to connected in right way by taking care of polarities of each transformer.

Regards and thanks.

all wrong !

I'm not sure your secondary circuit is Ok.

With 127 Volts secondary on each transformer you will get 254 Volts output where 220 V is required

"Since phase angle is 120Deg Voltage of each transformer=220/1.73=127

IF Connected in series total output voltage =(127+127+127) /1.73=220volts."

This is incorrect. The figure of 1.73 is the scalar solution for the vector sum of 2 sinewaves 120 degrees apart, i.e. 2 phases of a 3 phase system.

The scalar solution for the vector sum of all 3 phases in a 3 phase 120 degree system is...

wait for it...

...ZERO!

The correct answer is that it is not possible to load all 3 phases evenly with a single phase load. Not without significant energy storage and some kind of switching. Or a rotary converter. Which has energy storage in the form of rotating momentum.

The Scott system produces a 2 phase 90 degree output that can not drive a single phase load such that it evenly loads a 3 phase system. The 2 phase 4 wire system has actually four load peaks per rotation. Note that the positive and negative peaks are 180 degrees apart; it follows that any series resistive load will unevenly load the 3 phase input.

Also note that the transformer schematic in the earlier post shows a single core. This is obviously not a working connection and anyone with a passing knowledge of transformers would reject this diagram out of hand. E.g. it was not posted by someone very familiar with transformers and it's not likely a simple oversight.

Michael

I'm struggling to understand why the two secondaries of a Scott transformer can't be connected in series to produce one single phase output. By vector addition, the phase of this combined output would be at 45deg from each of the (unconnected) secondaries, and its open circuit voltage would be √2 times the open circuit of each of the secondaries.

On the other hand, there is another argument that says:

a) creating 3 phases from 1 phase feels intuitively very unlikely to happen

b) transformers are inherently bi-directional

c) therefore transforming 3 phases into 1 phase is also unlikely.

But I still don't understand why! Can you help?

Correction---

Please read word "inputs" as word "outputs" in para# 5 from top.

dear sir,

Can u give me your best possible price for 3 phase to 2 phase transformer Qty:3 nos

Capacity : 5KAV, Primary : 380V – 415V, 50Hz. 3phase AC supply.

Secondary : 230V. single phase AC supply.

380-415V / 230V, 5KVA Transformer.

regs

sudharsan

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