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Clarification transformer circuit

  1. Aug 7, 2016 #1
    attached image:
    the transformer taping is correct 120+120=240V?
    where i take taping of transformer nuetral point?
    the both are consider is 240V out put in two different faces?
    please if any wrong in circuit help me or it good i will proceed.
    here i attached circuit .pdf

    Attached Files:

  2. jcsd
  3. Aug 7, 2016 #2


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    In both drawings the primary is wired for 440 Volt.
    In the left drawing one secondary winding provides 120 V for the undercarriage socket circuit, the other 120 V for the under carriage lights.
    In the right drawing the secondary windings are in series for 240 V and both loads are in parallel.
    There is no grounding indicated: both sides are 'floating' with respect to ground. You could connect either of the two (but not both :smile:) to neutral but I see no reason to do so.
  4. Aug 8, 2016 #3


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    I recommend that the X2-X3 connection be connected to ground. This is to prevent charge build-up when there is a nearby lightning strike and also as a safety precaution in case the transformer fails with a short from primary to secondary. This is pretty much required in the U.S.A. except for some low voltage or specialized industrial use.
  5. Aug 8, 2016 #4


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    so you are going to ground a point that is going to be at 120V potential difference to ground ?

    I'm sure that's going to work really well, not

    @jim hardy ... can you do that in the USA ? really ?

    Do that here in Oz and many other countries and there's going to be a big bang
  6. Aug 8, 2016 #5


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    Did I miss something? What other point in the circuit is connected to ground in the diagram?

  7. Aug 8, 2016 #6


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    the neutral would be

    hence why I asked Jims advice, he knows the USA system better than me
  8. Aug 8, 2016 #7


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    (Referring to the schematic)
    If that is the case, the left side schematic already has X2-X3 connected to Ground, which is what was suggested.
    The right side schematic does not have a neutral and the suggestion was the same point be connected to Ground.

    Where does the problem arise?

  9. Aug 8, 2016 #8

    jim hardy

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    In US
    whenever you derive power from a winding, be it transformer or generator, you must provide a path for fault current back to that winding.
    The path must be stout enough to trip the overcurrent device. We call that "Bonding". That's important, so that a faulted device will disconnect itself from power.
    That the breaker opened also alerts you to the fault.
    There are exceptions for industry where it is expected they'll have trained people around ; they require automated monitoring and alarms for ground faults.
    A search on "Separately Derived Source" will be productive.

    The last Sola constant voltage transformer i was inside, a 2.5 KVA one, came with its secondary neutral already connected to its frame by a green wire.
    I would expect to find same in this genset (or whatever it is)
    and i'd make sure its frame is connected to vehicle chassis by a stout wire or bolt.


    ( Late Edit - i think i shoul'd've said not "earthed" but "bonded"
    because if it's a vehicle mounted genset there's tyres between its chassis and 'earth' that insulate
    and i see a typo on my other picture, word 'ground ' should have a quote" before 'g' not a colon:)

    i note they speak of "undercarriage" ? is this a vehicle mounted genset ? See my annotations to Mike Holt's sketch below...

    Thanks to dlgoff for this timely picture,
    and to Mike Holt - much credit is due that man http://www.mikeholt.com/instructor2/img/product/pdf/1292432628sample.pdf


    i hope this helps.

    Let us know what you see inside the genset...

    old jim
    Last edited: Aug 8, 2016
  10. Aug 8, 2016 #9
    The right side is modification proposed drawing
    my supplier replied me the i.e (We don't need to consider 120v port as it is in x2 & x3. We need to hook the field wiring on the port X1 & X4 for 240vac.)
    i will take neutral point at any other location in the circuit it will work?
    If their is any other way to modification please suggest me,
    above explanation left side drawings, please can you explain me right side circuit?
  11. Aug 8, 2016 #10


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    I might be wrong but i think most countries control who can authorize changes to aircraft systems. This seems like a question that should be referred to the relevant authority/expert?
  12. Aug 8, 2016 #11

    jim hardy

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    Aircraft ? I missed that part.

    I take it the question he answered was
    i agree with him, you do not need to run a neutral wire to your 240 volt outlet and your 240 volt light fixture.
    So you do not need to take transformer X2-X3 tap anyplace . However, I'd want it bonded to chassis .
    What does your supplier say about Bonding or Grounding ?

    You do need to install the correct 240 volt "undercarriage socket" though so that nobody can plug a 120 volt appliance or tool into it.
    And you do need to clearly mark the undercarriage light fixtures "240 volt lamps only",
    or if your 240 volt lamps use a different base than the 120 volt ones, install new fixtures.

    In US, "Neutral" is the current carrying conductor that is at effective ground potential.
    There will be no neutral wire departing from your transformer tap X2-X3.

    Accordingly, the right half of your drawing does not show a neutral conductor.
    I don't know what you meany by "take neutral point"
    you may call X2-X3 neutral , and that's what i would do.
    The wire that used to connect X2-X3 to lamps and undercarriage socket and lamps was a neutral wire and presumably was color-coded as such ; in US it'd be white but i dont know about color codes where you are.

    Since your undercarriage socket and undercarriage lights no longer have a neutral, you don't need to take X2-X3 anyplace except maybe ground.
    You do need to be sure that both of the wires going to each undercarriage light and each undercarriage socket are of proper color to indicate high potential, in US typically black or red , and are no longer the color that indicates neutral.

    Explain ?

    See if this annotated sketch helps.

    i realize English is probably not your first language... i hope i answered the right question..
    Physical wiring will look not at all like the schematic. If you are uncertain get help of an electrician who has experience on this machinery..

    What kind of installation do you have ? I've heard of marine installations that are ungrounded but never encountered one.

    old jim
  13. Oct 10, 2016 #12
    Dear Jim
    sorry for my late reply.
    i have checked all above your suggested conditions.
    i open neutral point from the circuit, when i checked at 219CB shows 257.06VAC. wire point (H16,H13).
    H16,H13 is connected our electrical control panel TB for out late sockets.
    i have traced the neutral cables of out late sockets and connected those points to connected neutral points of other transformer which is driving voltage only 220VAC to my printer & computer.
    after that i checked voltage at H16 with Neutral points shows:-187.6VAC & even H13 to neutral no change.
    after i have checked different neutral points available at main control panel i have not reached 220VAC at any point.

    attached checked points.:

    Attached Files:

  14. Oct 10, 2016 #13

    jim hardy

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    you wanted to turn left half of picture into right half if i recall correctly ?


    Where were the voltmeter test probe connected ? There are two of them.
    Did you read 257 volts from one pole of the breaker to the other, or from one pole to chassis ?
    I dong see a H16 or a H13 on your drawing. Did you mean L16 L13 ?
    If you read that voltage between L16 and L13 then it seems you have achieved what you were after, to double voltage at those outlets.

    Missing from your drawing is any connection to earth. See the green lines i drew on it in post #8.

    what you have probably done is removed the earthing wire from your circuit.

    Again i assume you mean L16 and L13 ?
    And i dont know what you mean by Neutral. Vehicle frame? If that's so, you are probably reading voltage of the floating unearthed system you made .
    In US it should be wired thus :

    I dont know about UK and European wiring. They might earth the transformer at one end not the middle.
    These drawings do not seem complete because they don't show grounding.
    You need to find out how systems are "grounded" in that equipment: solid, through impedance or through high impedance , and follow suit..
    How are the other circuits earthed ?
    And you really need to mark up the drawings and submit to responsible design organization, even if that's just your chief electrician.

    Don't take offense at this,
    but you really need to ask for help from someone who's familiar with the equipment you're working on.
    If this is an airplane that's somebody with an A&P license.
    CWatters inquired in post #10 and you never answered.
    I won't knowingly be a party to unauthorized changes to an aircraft. Nor would i expose Physics Forum to that liability.

    old jim
  15. Oct 10, 2016 #14
    Yes L16 & L13 only I measured 257VAC.
    Here L13 is connected to light circuit
    L16 is power out let circuit.
    The ground is not connected to X2&X3 points that point directly connected main electrical panel zero potential (neutral "N"). Earlier my images indicated TB point "N".

    My machine is container type generator with rail welding system.
    It's not vehicle chassis it zero potential return path we call Neutral point.
    This is not a airplane it just rail welding machine with container type inserted generator housing system.

    Am authority person to do electric works for this equipment,
  16. Oct 10, 2016 #15


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  17. Oct 10, 2016 #16


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    That is scary.
    That is good advice. Do not try to get professional electrical advice on a web forum as a substitute for hiring a competent professional electrician.

    Thread will remain closed.
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