Transformer windings configurations - what is the purpose of them?

Discussion in 'General Electronics Chat' started by zuababa, Aug 11, 2015.

  1. zuababa

    Thread Starter New Member

    Aug 11, 2015
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    I apologize if similar question was asked before - I tried to look for one but it drowned with dozen of questions about some calculations related to transformer configurations. I was reading a lot about the transformers, I understand how they work, but then I started reading about the windings and I got confused why are there so many types.

    I have background in computer science therefore I apologize also if my question is stupid or silly - but I have trouble understanding why do we need different configurations of the transformer windings? Is it some kind of backward compatibility issue? Or does it depend on the type of load? I see a lot of calculations related to different windings etc. but I don't understand why one type of winding is better than the other?

    Then, is there a tendency to choose some configurations over others, depending on the type of transformer? (e.g. the medium to low, or the high to medium). That could also help to understand why.

    Looking forward to your replies, I would appreciate some other references to read if you have.
     
  2. #12

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    Nov 30, 2010
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    There is a good place to focus. Better than what, All other windings? No. Every transformer is designed to do a particular job. Every winding is better than all the other windings in the world for the job that is required for THAT transformer.

    Would you want a telephone pole transformer in your headphone amplifier? Why not. The transformer on the pole is obviously better at moving power...and you want powerful headphones...don't you?
     
  3. MaxHeadRoom

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    Jul 18, 2013
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    As #12 says, the different types are for different applications, e.g. Toroidal wound power transformers use the magnetic field more efficiently and do not radiate a field like EI laminated do, one reason they were chosen for Audio amps etc.
    Practically all types operate on the very same principle.
    The design also changes with applied frequency, iron core - ferrite core etc.
    Max.
     
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  4. zuababa

    Thread Starter New Member

    Aug 11, 2015
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    But in case of power distribution, we have e.g. medium to low step down transformer and we have different types of winding configurations, such as wye or delta. Is it a case that different approaches are used or is it always that, eg. the configuration will be the same for all types of medium to low voltage step down transformers?

    #12, I don't know which type of transformer is better in my headphones, and yes, I enjoy them being powerful.

    I maybe didn't put my question precise - I only want to understand why would we consider to make a transformer from wye to delta, or delta to delta, or delta to wye, especially in power distribution.
     
  5. #12

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    Never mind. I was just checking to see if you could understand that a 900 pound power transformer isn't the right thing for your iPod.
     
  6. MaxHeadRoom

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    3 ph transformers can be connected Star/Delta to provide a different voltage input/output,
    The star connected can operate between any phases as well as phase to star.
    BTW there is no such thing as a 3phase transformer, it is 3 single phase transformers mounted on one frame, you can just as easily use 3 1ph types.
    Max.
     
  7. crutschow

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    Mar 14, 2008
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    But there are transformers designed for 3 phases that share a common magnetic core.
    To me, that's a 3-phase transformer, thus it can't be used for two single-phases, for example.
     
  8. MaxHeadRoom

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    Last edited: Aug 11, 2015
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  9. MaxHeadRoom

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    http://www.electronics-tutorials.ws/transformer/three-phase-transformer.html
    From above link:
    A three phase transformer or 3φ transformer can be constructed either by connecting together three single-phase transformers, thereby forming a so-called three phase transformer bank, or by using one pre-assembled and balanced three phase transformer which consists of three pairs of single phase windings mounted onto one single laminated core.

    The advantages of building a single three phase transformer is that for the same kVA rating it will be smaller, cheaper and lighter than three individual single phase transformers connected together because the copper and iron core are used more effectively. The methods of connecting the primary and secondary windings are the same, whether using just one Three Phase Transformeror three separate Single Phase Transformers.
    Max.
     
  10. crutschow

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    Yes, as shown in Figure 11.2.2.
    Because of the unique phase relation of the 3 phase signals, the flux in the common core is always in phase between the 3 windings. Don't ask me to explain it beyond that as that's the extent of my knowledge. ;)
     
  11. MaxHeadRoom

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    But they are all separate as far as individual flux affecting the different secondaries.
    So essentially from a practical point of view, they are three separate entities.
    Max.
     
  12. crutschow

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    Can't argue with that.
    But I would expect it takes less iron for the single core transformer as compared to three transformers, for the same power rating.
     
  13. zuababa

    Thread Starter New Member

    Aug 11, 2015
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    Correct me if I'm wrong: In power distribution, at the medium to low (ML) voltage transformer (e.g. 110/10kV), we mostly have delta to star transformer, because this way we can provide at the user side the 220 (phase to ground) /400V (between phases) (I'm in Europe). This is assuming that the user side is like a regular neighbourhood with houses. Therefore, can I assume all the ML voltage transformers have this type of configuration?
    While if we were feeding an industrial area, it could be that we needed to have a delta to delta transformer, as we need higher voltage (and this way we can achieve 440 V between the phases).

    What type would be prefered in High to Medium voltage transformers?
    Is this the right way to think about the choice of the winding configuration?
     
  14. cabraham

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    Oct 29, 2011
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    Not really. Take a 3-phase unit where 3 sets of coils are wound on the 3 legs of a pair of "E" shaped core halves. THey are not 3 discrete single phase units. Flux from phase A actually couples to that of phases B and C, etc. A 3-legged E core is known as a 3-phase "core type" of xfmr. It is definitely a 3-phase entity, not 3 single phases because the fluxes share magnetic paths.

    Claude
     
  15. MaxHeadRoom

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    They share a path but there is no , or cannot be an influence of one coil or secondary over another.
    Otherwise you would see a difference between a common lamination type to 3 distinct transformers.
    Max.
     
  16. cabraham

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    Oct 29, 2011
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    I beg to differ. Take a 1-primary 1-secondary xfmr wound on a 3-legged E core, aka a "core type" xfmr. Both primary and secondary are connected as "Y", with primary neutral not connected to the 3-phase source powering the primary. A load is placed from "a" to neutral on the secondary side. Say the line-neutrals are 120 volts, and line-line are 208 volts. The load from a to neutral is 40 ohms. What are the currents?

    On the secondary side, coils b and c are open, so their current is 0. Current in a and neutral is 120/40 = 3 amps. Primary currents are as follows:

    Ineutral = 0, since it is open.
    I_A = 2 amps
    I_B = 1 amp
    I_C = 1 amp

    With the 3-legged E core, the amp-turns relation among the coils is different from other xfmr types. The flux in leg "a" of the core has a return path through the legs of phases "b" and "c". Coils b & c on the secondary have 0 current, whereas coils b & c on the primary have 1.0 amps each. The phases in a 3-legged E core have both magnetic and electric coupling. With other types of cores, like 3-phase shell type, and 3 individual 1-phase types, the phases are electrically coupled but not so magnetically. A 3-legged E core's behavior is markedly different for this reason. I will elaborate if need be.

    Claude
     
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