Delta Connected and Star Connected Load Questions

Discussion in 'Homework Help' started by haseeb112, Dec 7, 2009.

  1. haseeb112

    Thread Starter New Member

    Dec 7, 2009
    hey can someone help me to work this out please,

    Each phase of a delta connected load comprises a resistor of 50ohms and a capacitor of 50microFarads in series,
    the three phase load is connected to a 440v rms, line voltage and 50Hz three phase delta connected supply, calculate:

    a> the phase and line currents
    b> the phase and line voltages
    c> the power factor
    d> the total true power (p)
    e> the reactive power (Q)
    f> the apparent power (S)

    and then repeat again for star connection same load.

    i tried to use the capacitor as a coil, but still could'nt do it, got me even more confused, plus i was'nt sure if i was to use 1/2.pi.f.l or just 2.pi.f.l

    Last edited: Dec 14, 2009
  2. mik3

    Senior Member

    Feb 4, 2008
    Calculate the capacitors reactance according the the capacitance and the line frequency. Find the total impedance for each phase and then the current through each phase. The rest is just formulas.
  3. haseeb112

    Thread Starter New Member

    Dec 7, 2009

    can you tell me what forumlas i have to use for the first two questions for delta
  4. mik3

    Senior Member

    Feb 4, 2008
    To find the impedance of the capacitor use:


    the impedance of the resistor (Zr) is just its resistance

    Then find the total phase impedance Zph=Zr+Zc

    Then the phase voltage for the delta connection equals the line voltage. Thus divide the line voltage by the phase impedance to find the phase current (Iph).

    The line current is Iph*sqrt(3)
  5. GetDeviceInfo

    AAC Fanatic!

    Jun 7, 2009
    Unusual approach.

    Xc = 1/(2*pi*f*c)
    R = R

    Zphase = sqrt(Xcsq + Rsq)

    Iphase = Vphase/Zphase

    In Delta Vphase = Vline, In Y Vphase = Vline/sqrt(3)
    In Delta Iline = Iphase * sqrt(3), In Y Iphase = Iline

    For the power triangle, pf = watts/VA. S and Q hold the same angular component as your impedance triangle.
    Last edited: Dec 8, 2009