Calculation of short circuits on power systems

CURVES presented in the companion paper “Standard Decrement Curves” are sufficiently accurate for most commercial work, particularly circuit breaker applications. Many special cases arise, however, for which these curves are not applicable. Of this character are relay applications on power systems involving several machines having different time constants and located unsymmetrically with respect to the fault. The individual branch currents in systems of this character may have widely different decrements and even may increase with time. Need, therefore, exists for a method of calculation which will take these individual variations into consideration. Such a method has been developed and has been termed the “internal voltage” method of calculation. It is particularly valuable in that it lends itself to the use of the calculating board and thus minimizes the labor involved.