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had working motor reconditioned , now tripping overload

Discussion in 'Electrics UK' started by lor, 10 Jun 2010.

  1. lor

    lor

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    hi,

    had working motor reconditioned , now tripping overload .

    motor was working fine, was sent to Dowding & Mills to be "overhauled and rebalanced together with the fan impellors

    3 phase 30kw induction GEC with condensate heater.58.5 amps

    now drawing 80 amps on all 3 phases and consequently tripping the overload protection . Had electricain check wiring with Meggar -ok
    also checked each coil to earth -ok

    any ideas please as stuck

    thanks a lot
     
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  3. ban-all-sheds

    ban-all-sheds

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    Send it back to the people who broke it.

    (PS - The Northern Mariana Islands aren't technically part of the UK, but the above advice is good world-wide.)
     
  4. ColJack

    ColJack

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    they've obviously rewound it wrong. didn't put the right amount of windings in, or not enough poles or something..

    as said, send it back and explain to them..

    why was it sent for rewinding? was it faulty?
     
  5. jeepmadmike

    jeepmadmike

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    Is The motor connected the same? ie star or delta? When it is running does it sound ok If it is making a loud buzzing there might be a winding reversed

    mechanically has what it drives been assembled correctly?

    As said get them to fix it or advise you
     
  6. Bolty

    Bolty

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    morning,
    Can you run the motor without any load?. if so, what current per phase are you drawing. is the motor mechanically overloaded?
    Check the motor control panel.. do you have a faulty contactor or high resistance across the contacts?. If the panel is a star delta starter, does it swap over?. These faults can give increased current drawn by the motor.

    it may be worthwhile checking the motor connections again, its not unheard of for a winding to be reversed after a repair or the connections to differ.

    In my experience, dowding and mills are very good and they should have test ran the motor before sending it back to you, perhaps a phone call to them to confirm it was test ran may be helpful.

    Good luck

    Bolty
     
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  8. holmslaw

    holmslaw

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  9. lor

    lor

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    thanks for all the replies,

    the motor is DOL

    it runs without humming

    it is turning an air impeller

    we have done exactly the same job on 3 other motors and they are ok

    the motors are wired in delta configuration

    the motor and impellor can be turned by hand freely.

    still suspect it may be something i've missed ...its a days work to strip down and send back so I have to be more certain.

    thanks again
     
  10. ericmark

    ericmark

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    Two things I would look at which really the same.
    1) Has it been rewound as star instead of delta?
    2) Have they selected correct voltage?

    In Hong Kong the tunnel boring machine was supplied with 10Kv and transformed to 660v and 220v the latter from delta winding and most of Hong Kong was same as UK 11kv and 415/240 and it was very easy for rewind motors to arrive back at 415vac instead of 660vac.

    I would be calling rewind people and confirming voltage. Maybe you can just run them in star instead of delta? We used star/delta start so was not an option.

    Also had problems when working for SLD pumps in UK with mines and quarries as it seems 660vac is common with them.
     
  11. matt1e

    matt1e

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    it is unusual for a motor to come back faulty after a rewind from a reputable company as they are usually tested (though it did happen to me once)

    here's what I would do
    1)get your sparky to measure the resistance between the coils again, it doesn't
    matter if the motor is configured for star or delta the resistance readings between the supply connections should be the same ie L1/L2 = L2/L3=L1/L3
    also check for leakage to earth

    2)if ok check that all three supply phases are present at the motor contactor and that they are roughly the same voltage with respect to neutral or earth
    (expect a small variation here)

    3)energise the contactor and check that all three phases are present at the overload terminals,(ideally at the motor terminals?)
    if the motor is connected then measure between the terminals for 400v and not to earth for 230v as you will get backfeed via the motor winding
    if there is the same volage between L1/L2, L2/L3 and L3/L1 then you can measure each phase with respect to earth (ideally at the motor terminals to determine how balanced the supply is

    but firstly it would be a good idea as ericmark has said to determine its voltage rating there should be a rating plate on the motor, but as its been rewound then a phone call to Dowding & Mills would be a better idea

    lastly just to clarify what ericmark means
    if the motor was rated say 400/680 before you sent it to them, then it would have been connected delta on a 3ph 400v supply
    if they have rewround for 230/400 then you would connect this in star to a 3ph 400v supply

    Matt
     
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