1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Synchronous generator phasor diagram

  1. May 24, 2016 #1
    1. Problem Statement:
    A 4-pole, star-connected, 50 Hz, 11kV, 40 MVA turbogenerator, with a synchronous reactance of 0.8 p.i., is connected to a power network. This power network can be represented by 11-kV infinite bus with a series reactance of j 0.5 Ω. A voltage regulator adjusts the field current such that alternator terminal voltage remains constant at 11 kV.

    2. Relevant equation:
    Based on the information above I can write the following equation:
    [itex]\overline{E}_ f= \underbrace{\overline{V}_{bus} + jX_{line}\overline{I}_a}_{V_t} + jX_{s}\overline{I}_a[/itex]

    3. The attempt at a solution:
    Based on the equation above I can draw the following phasor diagram. I just copied the one drawn in the book, due to my paint skills did not yield a pretty result.

    The phasor diagrams draws [itex]I_a[/itex] lagging with respect to [itex]V_t[/itex], and therefore [itex]\theta[/itex] is the angle between them.

    My question is: How do I know how to draw [itex]I_a[/itex]? I know that [itex]I_a[/itex] should atleast be lagging [itex]V_t[/itex] at lagging power factor, but could it not also be drawn lagging with respect to [itex]V_b[/itex] and then [itex]\theta[/itex] is the angle between [itex]V_b[/itex] and [itex]\theta[/itex]?

    I guess [itex]\theta[/itex] is defined from [itex]V_t[/itex] is because [itex]V_t[/itex] is chosen as reference phasor. But I am still confused by how [itex]I_a[/itex] is placed.

    Hope I made myself clear, and appriciate any help, best regards.
  2. jcsd
  3. May 28, 2016 #2


    User Avatar

    Staff: Mentor

    I'm a bit rusty on synchronous machines, what does p.i. mean?
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted