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  1. Kj14
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    Kj14 EF Member

    Location:
    United kingdom
    Hi I need some help I haven't work on star delta motors since my 1st year apprenticeship. How do you test the motor from the panel i.e check that the windings are balanced?

    Any help much appreciated
     
  2. telectrix
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    telectrix Scouser and Proud of It Trusted Advisor

    Location:
    cheshire/staffordshire
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    Telectrix
    you could clamp each phase. see if each was equal current.
     
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  3. Andy-1960
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    Andy-1960 Electrician's Arms

    Location:
    Wolverhampton
    Depending on the type of load you may find doing a current test on each phase does not always give the answer you may expect. It may be fine on a load such as a fan, but I have a customer that manufactures compressors and we always get out of balance current readings.

    Testing in the panel across each set of windings with a good quaility meter should give a matching resistance across all three windings, so test between U1 & U2, V1 & V2, W1 & W2. Then megger test each winding to earth.
     
  4. PEG
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    PEG Trusted Advisor

    Location:
    Manchester
    Hi,depending on constraints,if it was the motor i was wanting to test,i would not include the wiring from panel to motor. Check as described,but at disconnected motor.

    This way,any troubling readings are the motor,and not any included part of the connections.
     
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  5. Andy-1960
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    Andy-1960 Electrician's Arms

    Location:
    Wolverhampton
    Testing at the motor with it disconnected would always be my preference, but the OP did ask how to test from the panel so I assumed there were constraints.
     
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  6. Pete999
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    Pete999 Trusted Advisor

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    Location:
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    No such animal as a Star Delta Motor, it's the method of starting that Star Deltahttps://www.youtube.com/watch?v=KsS1v_i2YtU
    Best way to check the Windings would be to disconnect the 6 leads at the Motor terminal box, make sure you mark the leads, to avoid malfunctions
     
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  7. PEG
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    PEG Trusted Advisor

    Location:
    Manchester
    ...Like that massive circular saw,not cutting as well as previously...;)
     
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  8. Andy5678
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    Andy5678 EF Member

    Location:
    Scotland
    What is the purpose of the test, maintenance or do you suspect a fault?
     
  9. Kj14
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    Kj14 EF Member

    Location:
    United kingdom
    The motors getting hot and tripping out Ive insulation resistance tested and that's fine, just want to check the motor is balanced. Need to rule out electrical fault before fitters will look it
     
  10. Andy5678
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    Andy5678 EF Member

    Location:
    Scotland
    Can you turn the rotor to make sure it turns free and smooth, is there any noises coming from it when it's on, if there's a belt on it is that ok and tight enough. Also check if the overload is set properly
     
  11. Andy-1960
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    Andy-1960 Electrician's Arms

    Location:
    Wolverhampton
    Is it changing from star to delta?
     
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  12. PEG
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    PEG Trusted Advisor

    Location:
    Manchester
    Perhaps,most importantly of all,what is the motor driving?
     
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  13. mickfred
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    mickfred Regular EF Member

    Location:
    Liverpool
    Won't be the starter , most likely bearing gone , damaged fan or belt too tight .
     
  14. Andy-1960
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    Andy-1960 Electrician's Arms

    Location:
    Wolverhampton
    How can you say it's not the starter? I have seen motors that have been stuck in star either because of a failed timer or even a welded star contactor and boy does the motor run hot!
     
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  15. mickfred
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    mickfred Regular EF Member

    Location:
    Liverpool
    BECAUSE I SAY ITS NOT ( please don't be the starter )
     
  16. mickfred
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    mickfred Regular EF Member

    Location:
    Liverpool
    if my thinking right the current (in star) of each phase runs across two sets of wiring doubling the resistance and reducing the current therefore why would it be getting hot
     
  17. Andy-1960
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    Andy-1960 Electrician's Arms

    Location:
    Wolverhampton
    Because of the load on the motor, it cannot deliver the required power, torque and will not achieve its maximum running speed when running in star hence the motor will be overloaded.
    When the motor is connected in star, the motor will be effectivly rated at approximately a third of its motor plate rating, so a 7.5kw rated motor will have an output of about 2.5kw. So if the motor is being asked to deliver 7.5kw of power but only capable of delivering 2.5kw it will effectively be overloaded and get rather warm! The control system will not normally detect this as usually the overload relay is shorted out by the star contactor during start up.
     
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  18. mickfred
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    mickfred Regular EF Member

    Location:
    Liverpool
    Fair enough it's still not the starter
     
  19. Andy-1960
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    Andy-1960 Electrician's Arms

    Location:
    Wolverhampton
    Lol.. it may not be, you may be right but worth a check all the same.
     
  20. mickfred
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    mickfred Regular EF Member

    Location:
    Liverpool
    Okay check it switches over and when it does check what i said (god , i really hope it not the starter )
     
  21. ipf
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    ipf Trusted Advisor

    Just an example.
    One panel I installed over 30 years ago controlling 4 x 15kw motors via s/d starters. In all those years the motors have all been changed just once with the odd bearing change, whilst I would say that at least 25 contactors have needed changing with contact damage due to load.
     
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  22. Kj14
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    Kj14 EF Member

    Location:
    United kingdom
    It's switching over and it will run for a while sometimes a few hours and then trip. It's running a vac pump. Just need to know how to test winding from the panel as the motor box is not easily accessible.
     
  23. Pete999
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    Pete999 Trusted Advisor

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    Northampton
    Are you talking IR or resistance testing
    Are you talking IR or winding resistance testing
     
  24. stantheman
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    stantheman Regular EF Member

    It could be a multitude of things, does the motor sound ok? rumbling or knocking noises could indicate bearings/ alignment problems, check the supply voltage at the panel (line to line and line to earth) then from there visually check for bad/burning connections ( does the panel smell of burning when first opened up?) then carry out all the dead testing checking contact resistance on all poles of the contactors not forgetting to check the resistance of the overloads themselves. Check that the resistance of the motor windings from the panel are balanced if not check at the motor terminals.
     
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  25. stantheman
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    stantheman Regular EF Member

    I've just seen that it's a vac pump, when these start to fail they can become very noisey (sticking or broken blades) and at the same time take longer to reach the preset vacuum (this can checked by asking the operator if they have noticed any changes).
     
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  26. DAvid Prosser
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    DAvid Prosser Regular EF Member

    Location:
    UK
    I'm going for mechanical fault (or lack of maintenance) on the vacuum pump. Oil and filter candles need changing. Just a complete guess but as I can't see it, hear it, or test it I'm just having fun guessing.
     
  27. Kj14
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    Kj14 EF Member

    Location:
    United kingdom
    Winding resistance from the panel
     
  28. Pete999
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    Pete999 Trusted Advisor

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    Location:
    Northampton
    At which contactors? you will need to identify the 6 cables going to the motor
     
  29. Kj14
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    Kj14 EF Member

    Location:
    United kingdom
    That's what I need to know I can see the star contactor and the delta contactor
     
  30. stantheman
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    stantheman Regular EF Member

    Check at the main contactor and the delta contactor not forgetting the o/l unit. Identify the windings U1 start and finish U2, V1 & V2 and finally W1 & W2, these should have the same value, don't be surprised at the very low impedance readings. Also check for leakage to earth from U, V and W. Don't forget to check the input voltage.
    If all above are present and correct including what was said in #24, then it's almost certain a mechanical problem.
     
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    Last edited: Mar 29, 2017
  31. stantheman
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    stantheman Regular EF Member

    What was the outcome?
     
  32. theguz
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    theguz EF Member

    Location:
    glasgow
    make sure all the contacts in the contactors are making . you might be losing a phase
     
  33. stantheman
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    stantheman Regular EF Member

    The fault has probably been fixed by someone else as the op not been back with any info.
     
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