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Motor Accel Calcs

  1. May 10, 2006 #1
    Hi everyone, I'm a Technologist in Training, except that I'm not getting much training. I have a tonne of questions regarding Motor Accel Simulation in ETAP. I'm hoping someone here might be kind enough to lend some insight, or point me to a place where I can find some.

    First off, has anyone done this in ETAP? I've got some setup questions that I'd like to post, but will spare for now until I know there is someone who can help.
    Second, can anyone tell me how this is done outside of ETAP (or other sim software)? I know how to find LRT, LRA, etc But how does this relate to startup and Voltage Flicker Regulation? (I do not know at this time if the 1100hp motor is being started under load or not). Essentially, how is this done by hand so I can validate my simulation?

    I have to do a simulated startup and confirm that we need a SS instead of doing DOL, because the DOL lowers our voltage below Fortis' 5% minimum standard.

    Cheers if anyone can lend a hand. Thanks Gents,

  2. jcsd
  3. May 11, 2006 #2


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    Staff: Mentor

    Welcome to PF. What do the acronyms ETAP, LRT and LRA stand for? Can you give a pointer to a web page describing the simulations that you are asking about?
  4. May 17, 2006 #3
    Sorry for my late reply, I've been busy at work setting up this simulation. And I also made a quick reply earlier this week, but it was deleted by a moderator. I said or did something that violated the posting rules.
    ETAP - is the software package I am using to run the simulation, I cannot provide any links to this software package' website as it will violate the terms of posting.
    LRT - Locked Rotor Torque
    LRA - Locked Rotor Amps

    %Voltage drop is a differential equation and a very simple one, but what I'm having trouble figuring out is how do I determine the voltage drop of the motor when I have a Soft Starter, and when I don't? I'm assuming that since there is a controlled application of voltage to the motor, there is a controlled application of power. If it is gradually increased, the emerging magnetic field does not demand such a high in-rush current during start-up. What my problem is, is, how do I determine this by hand to verify my computer simulation in ETAP? I'm not sure how to determine voltage drop of a motor when using Soft Starting, or DOL (Direct Over Line, No Soft Start) starting. The difference between the two on the same motor will give me my %Vreg.

    Again any help you can provide is appreciated.

  5. May 23, 2006 #4
    Well my simulation is showing 10.1% Voltage Drop.

    If anyone can provide any assistance please let me know.

  6. May 24, 2006 #5
    For anyone interested:

    Vm = Zm / (Zm + Zl)
    Vm= Voltage during start-up
    Zm= Locked Rotor Impedance
    Zl= Impedance sum of source, line, xformer impedance
    *All values I used were per unit rectangular.

    As taken from the "Large Motors On Limited Capacity Transmission Lines" article by H.W. Lewis, Member IEEE, Williams Brothers Engineering Company and F.A. Woodbury, Member IEEE, Westinghouse Electric Corporation. Conference Record 77CH1229-4-LA, Paper Number PCI-77-41 Dated February 12, 1985.

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