Overload ups

Discussion in 'General Electronics Chat' started by Eng Majed, Sep 16, 2009.

  1. Eng Majed

    Thread Starter New Member

    Sep 16, 2009
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    Hi every body,

    I face probelm during comissioning of one project , and I hope that I will find answer here.

    My system is like this:


    I have 200Kva UPS feeding 100Kva Step-Up Trnasformer.

    this step up tr feeding 3 s/dawn transformers


    step/up is y-delta connection


    from UPS DP I connect 3-Phase to my LV side of the Tx.

    then I connect the Neutral in the Y side of Tx to Ground.


    what I 'm facinf now is Inverter Overload


    it shows 230 Amp L1,, L2 L3 in UPS Reading 120% over load


    then the UPS switch to ByPass.


    when it switch to Bypass the reading of the current is view Amps .

    the load drawn for the 3-step-dawn Tx is working well (which is cameras)

    I calcualted my load which will not exeed 30 Kva.


    I don't know why when I switch the operattion of the UPS to the Normal (through Inverter) it shows over load !!??


    I did one thing.

    I switch off the load of one of the 3 step-dawn Tx. but still the load same 120% over !!


    finally you may need to know


    UPS Output voltage is 380V

    while my Step up Tx input is 400V (suppose to be) 400v/13.8Kv


    can some body advice me?
     
  2. mik3

    Senior Member

    Feb 4, 2008
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    Maybe the UPS is faulty. Another case is if it does not output a true sine wave but it outputs a square wave. In this case the transformer will draw much current and cause over load.

    Is it a three phase UPS?
    Does it have a neutral wire or just three wires?
     
  3. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Mind me asking but Eng Majed... where are u from?

    Rifaa
     
  4. Eng Majed

    Thread Starter New Member

    Sep 16, 2009
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    Dear Mr. Mik,

    Thanks for your reply

    My UPS is 3-Phase

    It has Y out put , yes it has Nutral.


    this is the photos for the two cases






    [​IMG]






    [​IMG]
     
  5. Eng Majed

    Thread Starter New Member

    Sep 16, 2009
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    Knowing my place will help me :) ??



    KSA
     
  6. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    just curious
     
  7. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
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    Can we guess :)
     
  8. Eng Majed

    Thread Starter New Member

    Sep 16, 2009
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    guys I told you KSA Kingdom of saudi Arabia :)


    Now after you now may place can you help me please :)
     
  9. wr8y

    Active Member

    Sep 16, 2008
    232
    1
    If there is no load on the transformers, then it MUST be a poor waveform from the UPS OR somehow you have the transformers wired wrong.

    What else could it be?
     
  10. mik3

    Senior Member

    Feb 4, 2008
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    What does the box on the right contains?

    Just switches?

    Maybe the fault is inside this box.
     
  11. Eng Majed

    Thread Starter New Member

    Sep 16, 2009
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    Good Afternoon dears,

    I took these reading


    actually the load current is allways 220-230Amp


    see:

    I check My Tx (Load Side) the amp/rating is : 220amp-230amp- L1,L2,L3 In all cases ( Bypass & Normal Op)


    UPS :

    Bypass Mode

    Input-1: 220Amp-230amp L1,L2,L3 (BP Tx)

    Input-2: 30-40Amp L1, L2,L3 (to Rect.)

    Output:210-230Amp


    Normal through INV :

    Input-1: 15Amp-20amp L1,L2,L3 (BP Tx)

    Input-2: 120-140Amp L1, L2,L3 (to Rect.)

    Output:210-230Amp






    the BOX IS Synch between two modes
     
  12. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
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    It appears that the right hand box is the auto transfer function from Line Power to Inverter Power being fed to the output. If one of the triacs on either line or inverter feed is shorted, it would try to tie the two together. Phase (frequency) variance between the two could cause massive currents.
     
  13. rjenkins

    AAC Fanatic!

    Nov 6, 2005
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    If I understand correctly, the step-up transformer is Star wound on the 400V side and Delta on the 13.8KV side?

    If so, ensure the inverter is grounded correctly by any specific ground terminals, but do NOT ground the star point of the transformer primary.

    If the inverter waveform is slightly off, that could cause unreasonably high currents and upset things.

    As (in effect) a power source, it's own internal 'output neutral' should be internally grounded, or simply passed through from the incoming supply. Forcing another neutral could be causing large circulating currents.

    If I've misunderstood and the TX 400V side is Delta with the 13.8KV side Star, then the star point to ground sounds reasonable.
     
  14. Eng Majed

    Thread Starter New Member

    Sep 16, 2009
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    Apprecite your reply Gents.

    I feel that if there is somthing wrong it would be in the transformer side.

    Mr. Robert,

    I thing your advice is resonable.

    I will told you somthing. the problem is not in the UPS side (what I bleive).

    the reasone is in bypass mode the current still high.

    bypass mode means no relation of the Inverter.

    you mentioned that Neutral in star side of Tx should not be grounded.

    can you explain more please? cuz I want to try this.
     
  15. Eng Majed

    Thread Starter New Member

    Sep 16, 2009
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    other thing dear,

    if you mean that mybe there is lakage of the current via Nutral. I already check nutral there is no any lakage.


    I want to ask if my calculation is correct.


    100Kva Transformer

    100000/380x1.73 = 153 Amps . I belive that this should be the Max current drwan by Tx . so why 230 Amp !!!???
     
  16. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    You forgot to include the power factor and the efficiency of the transformer in your calculations.

    Try to connect the transformer directly on the output of the inverter (before the switch box). If the circuit works fine then the problem is inside the switch box.
     
  17. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    1,015
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    Mik3, I belive the 'switch box' is a virtual component on the UPS monitor screen?

    You are likely spot on with the power factor problem.

    If so, fitting power factor correction gear after the load transformers should reduce the load current by a very significant amount & probably pay for itself relatively quickly.
     
  18. Eng Majed

    Thread Starter New Member

    Sep 16, 2009
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    Mik,

    The switch box is not the issue . it dosn't have any action on the INV out put.

    as for the calculation . according to my knwoldg if I want to calcute the current for 3-Ph


    KW/PF= KVA VA/V = A then you need to devide be RMS =1.73 .

    Still I belive If somthing wrong should be Tx Side.
     
  19. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Eng, Majed
    You know I have seen that UPS from somewhere.

    Saudi, sorry my bad.
    We have one in the hospital


    Rifaa
     
    Last edited: Oct 5, 2009
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