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Homework Help: The torque curve of a indcution motor (laboration task)

  1. Nov 28, 2012 #1
    1. The problem statement, all variables and given/known data

    I have to measure the entire torque curve and stator-current of a inductive motor from idle running speed to 0 rpm. This will bee done for 130 V instead of 400 V because the energy loses will be too high if it is done with a stator voltage of 400V.

    Question: How does the inductive motors stator-current and torque vary with the stator-voltages amplitude? Find the formulas to re-calculate the already measured torque and stator-current so it is valid for the 400V case which isnt measured. It has to be valid for all rotational speeds n rpm. So it will be treated as an unknown constant through the deduction. Because for example the current at 130V and a specific rotational speed will be calculated for 400V at same rotational speed. Explain in words why the stator- current and torque vary like this.

    [tex]I_{S400V} (n) = I_{S130V} (n) * ...[/tex]
    [tex]T_{400V} (n) = T_{130V} (n) * ...[/tex]

    2. Relevant equations


    3. The attempt at a solution

    [tex]I_{s130} = \frac{P_s}{\sqrt{3}Ucos(\phi) }[/tex]

    Since the ratio of 400/130 is 3 we can express


    And for T:


    Since [tex]P_δ [/tex]depends on the voltage as does [tex] P_s (P_δ=P_s -P_{CuR})[/tex]

    then [tex]T_{s400} = T_{s130}* \frac{1}{3}[/tex]

    Now if this is correct (havent taken the resistance losses into account) how do i make it dependent of n? (n is the rotational speed in rpm)
  2. jcsd
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