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Induction motor at low voltage

  1. Dec 3, 2008 #1
    I have got an 1HP induction motor rated at 230V(line), 60Hz. If I run it at 185V(line) at 65Hz, what factors are affected in its performance?

    I am hoping for your expert advices..
  2. jcsd
  3. Dec 3, 2008 #2
    If this is a single phase motor it may have starting issues and will have less torque in general regardless of single or 3 phase. I believe wiki has some good stuff on variable frequency drives. You will likely get some good ideas from there.
  4. Dec 3, 2008 #3


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    At this lower voltage, you might start to see the motor getting a little warmer than if it were running at the rated voltage. It's probably not going to be enough difference to cause too much concern however I would want to try it to see. What is your application?
    For induction motors, as Averagesupernova says, it might have a little trouble starting. Again you can try it to see.
    Here's a Wikipedia page explaining how slip effects induction motor speed.
    Induction motors

    Welcome to PF
  5. Dec 4, 2008 #4


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    By my cacluations you'll be running about 74% flux density, get about 60% peak torque and as little as 54% starting torque.
  6. Dec 4, 2008 #5
    I see that lower voltage means not so good performance.

    My confusion is, if that is the case, why constant v-f is so popular. I will make my confusion clearer.
    For V-f, inverter is used to generate three phases. Inverter is fed by DC bus voltage which itself is rectified from supply voltage.
    Here is the problem,(step by step)
    -if supply voltage is 208V line,dc bus is 294V. (using three phase bridge rectifier)
    -Since max. phase voltage (from inverter) is only 0.5Vdc (about 150Vdc)
    -So,the motor driven at 208V directly is now only driven at sqrt(3)*150V/sqrt(2)=184Vrms
    line voltage.
    -Since all other V's and f's for const v-f is scaled from 184Vrms, all other values are skewed
    in their performances too.

    I went through different VFD for v-f, and almost all uses same scheme. Am I missing something here?
  7. Dec 4, 2008 #6


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    I'm not sure what you are asking here, but the general rule is to maintain a voltage to frequency ratio (V/f) to maintain the motors rated torque (230/60 in this case). So you can speed up or slow down the motor while keeping the torque constant. If you want to decrease its toruqe, reduce the V/f ratio.
    Variable-frequency drive
  8. Jun 10, 2010 #7
    Can you please explain or show your calculations for this? I have an induction motor that is nominally 400V 50Hz and I would like to know how its torque changes when running at 400V 60Hz. Thanks.
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