Verifying homework

Discussion in 'Homework Help' started by EL7819, Apr 17, 2011.

  1. EL7819

    Thread Starter New Member

    Apr 15, 2011
    20
    0
    Hello,
    I wanted to know If Im doing this question correctly?

    1.)A voltmeter, a PF meter, and a wattmeter are connected to a balanced 3 phase, 4 wire load. The Readings are 1500 Watt, 0.50 PF, 120 Volts. What current flows?

    This is my understanding so far: There are 3 branches and 1 neutral branch to the transformer. If it is balanced then each branch excluding the neutral, has 500 Watts.

    (120Volts)(0.50PF)(3)=500Watts---------> 180=500Watts/180= I=8.33A

    Or I worked it out this way too..


    (120Volts)(0.50PF)(SqRt3)=1500Watts

    60*1.732=1500Watts

    103.92=1500W/103.92=14.43A These both are two choices that are answers listed to the problem. Im having trouble understanding using the square root of 3, or multiplying with 3 for 3 phase systems. Are there any resources that will help me understand this better? I think it would be the 1st way but I'm not sure. Any help is greatly appreciated.
    Thank you.
     
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    Either answer could be correct depending on whether the stated voltage of 120V is the line-to-line voltage or the line-to-neutral voltage. The question doesn't make that clear, although it is more likely to be the latter. In that case 8.33A would be the correct answer.
     
  3. EL7819

    Thread Starter New Member

    Apr 15, 2011
    20
    0
    Thank you.
     
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