3 Phase Y Connected Generator

Discussion in 'Homework Help' started by richDFC, Nov 25, 2012.

  1. richDFC

    Thread Starter New Member

    Nov 25, 2012
    Hi guys.

    Got a question for a tutorial sheet we're doing and can't rap my head around the values I've worked out.

    heres the question

    A Y connected, 400V (line), 100KVA rated, stand alone generator is operating at 80kW at rated current with a lagging power factor and rated terminal voltage. The synchronous reactance is 2Ω.

    Draw the per phase equivalent circuit and calculate:

    (i) The Phase Current (Iph)
    (ii) The Power Factor
    (iii) The Reactive Power
    (iv) The Voltage drop across the Synchronous Reactance (VXS)

    So I've drawn the per phase equivalent circuit.

    I then calculated the phase voltage by Vph = Vline / root3 to get a value of 230.9V

    Iph was then found from S (apparent power) = IV rearrange to get I = 57735 (per phase power)/230.9

    This gives a value of Iph as 250A which seems slightly high.

    Continuing on i find power factor to be 0.8 from P = IVcostheta where costheta is the power factor.

    The problem comes when I calculate part iv the voltage drop.

    I used Vxs = Iph * jXs (j being imaginary number) but this gives a value of 500V which is greater than Vph.

    Any help is much appreciated!