3 Phase Motor with star delta starter shuts down after around an hour

Discussion in 'General Electronics Chat' started by niraj_khadka, Aug 21, 2016.

  1. niraj_khadka

    Thread Starter New Member

    May 10, 2016
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    Hello all.
    In our village we have a local community owned water distribution system where we use a 12 hp motor with a 12 hp motor starter (star delta) to pump the water.
    The star delta starter have the following components:
    1) Metasol MC-22b contactor
    2) Metasol MT-32 thermal protection relay
    The picture is attached herewithin.

    Previously due to low power issue on our village the motor was run on a DOL mode that is directly from the middle contactor and both the thermal realy and the primary contactor was byapssed. This way the pump was running fine although the submersible pump wires were a little warm.

    Now we bought a 60kva voltage stabilizer and conntected it. Now the motor is also connected as it should be in star delta starter. The motor runs okay for an hour and shuts off automatically. The thermal protection relay MT-32 is so hot to touch .
    The phase to phase current are as folows as shown by the ammeter display
    RY -----> 22A
    YB ------> 22A
    BR -----> 22A

    Before shutting off itself the ammeter reads around 26A.

    Since this is a phase to phase current and the motor only starts in star connection but runs on delta connection later so it means that the line current is root(3) times phase current which is over 40A, the limit of MT32.
    Please see the picture of how the starter was connected previously.. 1.jpg 1.jpg 2.jpg 1.jpg 2.jpg 3.jpg 4.jpg 5.jpg 6.jpg 7.jpg
     
  2. niraj_khadka

    Thread Starter New Member

    May 10, 2016
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    pic 3rd and 5th is the new connection style.. and others pictures are of old...
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
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    What is the FLA on the motor plate?
    Is the inlet and outlet of the pump fairly wide open (full load), if so you may need to reduce the outflow side somewhat.
    I assume the thermal relay has tripped at the point it stops?
    Max.
     
    Last edited: Aug 21, 2016
  4. niraj_khadka

    Thread Starter New Member

    May 10, 2016
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    My guess is the same but i think its not good to replace a thermal realy with a high ampere one because in the metasol datasheet it is given that mc-22b is supposed to use mt-32, and if i need to use mt-64 i neeed to chage the contactor as well..
     
  5. niraj_khadka

    Thread Starter New Member

    May 10, 2016
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    Another important thing.. The phase to neutral voltage in nepal is suppose dot be 220v but in my village the volatge is only 170V.
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,515
    2,369
    170v is definitely aggravating the problem, It is best to go to the cause and remedy that rather than increase the Th. relay, a bit like retouching the X-ray's instead of having the operation!;)
    What is it between phases?
    Max.
     
    Last edited: Aug 21, 2016
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,515
    2,369
    An aside: It seems rather strange that the three phase appears to be wired in Earth wire conductor/colours in some instances?
    Maybe this was an excess inventory and on hand or Kathmandu has a different standard ?:(
    Max.
     
  8. tcmtech

    Well-Known Member

    Nov 4, 2013
    2,034
    1,633
    That's your problem right there. The motor is running way below it's designed minimum working voltage which pushes its current draw up above it and the protection circuitries intended working limits.

    If it took 22 amps per phase at its normal 220 VAC input rating to put out 12 HP to do so at 170 volts input would require ~28.5 amps thus leading to your motor and thermal overload devices running way too hot for too long of periods of time.

    If you have a voltage stabilizer unit on the system what is its input and output voltages when all of this is happening?

    If it's what is putting out 170 volts obviously it's not able to raise the input line voltage high enough for the motor to work properly or it's wired wrong.
     
  9. ballie247

    New Member

    Jul 22, 2011
    1
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    A very often ignored problem in remote areas is that of power factor / power factor correction. Everybody adds induction motors to the utility supply and seldom adds local capacitors for power factor correction for the specific piece of equipment being connected. Cumulatively, this adds to a bad power factor at your connection point to start with. In my experience in a wheat and maize mill, bad overall power factor caused motor overheating and even failures. When a plant-wide assessment was done and primary incoming power factor correction was implemented, these problems disappeared. Then there is also the little matter of harmonics. (different but related can of worms) Lots of information is available on the net. I placed a link that could just help clarify some of the basics.

    http://www.plantengineering.com/sin...-factor/fb7e4029c995bb046039cb9d70b1fc6b.html
     
  10. Valentinas Svaplys

    New Member

    Aug 22, 2016
    1
    0
    Check your lines if there is possibility you can install step up transformer with automatic compensation of voltage change. But I think this is expensive. The only problem is that you can burn your pump, luckily it is in water. Maybe installing thermo protection inside pump and increasing amperage of thermal protection will solve problem. But if thermal protection, or thermal fuse fails you can burn your pump if it is very expensive this plan is bad.
     
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