For a three-phase fault at the spark location shown in the figure below with all equipment three-phase and generator of finite size, determine the symmetrical  rms fault current. Ignore the series resistance (but not the reactance) of the transformer and the generator. Assume all cables short with negligible R and X, and follow the following steps:

(1) As is commonly done by power engineers, convert the system to % values based on the kilovolt-ampere and voltage ratings of the transformer feeding the fault. Then, determine the fault current in amperes at the fault location and also at the generator terminals using the voltage ratio.

(2) Repeat the calculation by converting the system to % Z values based on the kilovolt-ampere and voltage ratings of the generator, and then determine the fault current in amperes at the generator and the transformer terminals and compare it with (1).

Transcribed Image Text:

√2 E/Xa √2 Ej/Xa √2 Eg/Xa + Ifault E Prefault field excitation voltage of generator = Subtransient I" Envelope of positive peaks of fault current Transient I' Steady state I