Control of AC Motors

Discussion in 'The Projects Forum' started by gorayausman, May 16, 2013.

  1. gorayausman

    Thread Starter New Member

    May 16, 2013
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    I want to Speed Up/Speed Down 5 Ac motors which are three Pahse and I want to control them with a Single knob.
    Three Motors are of 37KW while two of them are 1.7 KW.
    Can anyone Help me from where I should start and what will be the procedure???
     
  2. Kermit2

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    Feb 5, 2010
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  3. strantor

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    5 appropriately sized VFDs, with all their pot input 0V terminals tied together and all their pot input "wiper" terminals tied together, but only one +V terminal powering the pot.
     
  4. gerty

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  5. strantor

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    I usually see those used where one or both of the signal are not isolated, or where different voltages are used. For 5 VFDs using isolated 0-10V signals, it is fine to tie them together; I have done it several times with no issues. You only use one of +10V supplies though.
     
  6. gerty

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  7. cts_casemod

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    May 14, 2013
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    You could also use a 40KW VFD for all the motors. Just note that on this case the smaller motors would not be protected against overload.

    I believe in your particular application, since the load of the two smaller motors is so small in regards to the 37KW. it would be safe to add an overload relay to each of smaller motors. The drive would not suffer damage if one tripped as the output was still attached to the larger motor, that was being protected by the unit if the settings were entered correctly.

    Another way would be to a define one of the outputs of the main drive as a frequency or voltage output proportional to the motor speed and set the remaining ones to respond to this (PID feedback). They would self adjust in a master slave configuration in response to the master where the POT or Keyboard speed control was being used. This could be particularly useful if the smaller motors were to respond to a variation in the load of the first one as it often happens with FANs in cooling applications
     
  8. strantor

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    For lunch, the master speed and ratio pots. If you want 2 more more motors to be synchronized but at different speeds, you can use a similar common speed signal scheme. For example, when making rope or cable, there is a specified "lay length" (think 'period of a wave'); in order to achieve the proper lay length, there is a specific ratio between speed of twister (motor A) and speed of puller (motor B). The actual speeds of these 2 motors don't matter as long as the ratio remains the same. So you can tie the commons (0V) of the 2 drives together and use only one of the +v's, same as before, but the output of the pot goes to another pot, and the wiper of that pot goes to the second motor. The first pot is "master speed" and the second is the "ratio" pot. This way you can set the ratio at very slow speed and get it perfect, without wasting too much material, then use the master speed pot to increase the speed all the way to max, while maintaining the exact ratio (lay length). The same thing works for extrusion (line speed vs. extruder speed) to control the girth of the product, and probably on something like a food conveyor, and lots of other things.

    I don't have anything for supper.
     
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  9. strantor

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  10. gerty

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    Is that 3 motors @ 37KW ea or total?
     
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