Thermal Stress

Discussion in 'Homework Help' started by mo2015mo, Feb 7, 2014.

  1. mo2015mo

    Thread Starter Member

    May 9, 2013
    Hi my friends,,

    While I were studying a Synchronous Generator , I faced two questions are

    1. Which the type of load (leading or lagging) needed a large field current(lf) to maintain the rated voltage??

    2. Which the type of load (leading or lagging) placed more thermal stress on the generator ? Why?

    I know the answer for 1st question is lagging load according to solved example results written in my textbook is Electric machinery fundamentals.
    {At same rated value 480volts for lagging load If equals to 5.7A and for leading load If equals to 4.1A; Ea = Vt - Ia(Ra+jXs) }
    But ِِAre there any other causes to ensure that the largest If for lagging load??

    In second question I don't know anything about thermal stress and my textbook don't say any information about this subject,, Is there someone can explain to me about that?? In order to answer the question.. :) :)

    please help me and thanks advance :)
  2. kkazem

    Active Member

    Jul 23, 2009
    It's been awhile since I've done these calcs, but here it is. For your 1st Q, no, it will be higher current for lagging load. For your 2nd Q, I think it's again lagging as there is more field current causing more losses and more heat with more thermal stress. Regards, Kamran Kazem.
    mo2015mo likes this.
  3. mo2015mo

    Thread Starter Member

    May 9, 2013
    Thank you for your very useful information
    Mr. Kamran Kazem :)