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Good Afternoon

The Equation, in ASCE 113 2nd Edition, for determining values of Short Circuit Forces in Aluminum Rigid Bus in a Substation, is presented in Section 3.1.8.1, Eq. 3-38.  To account for partial decay of the DC component of the fault force a Decrement Factor, defined in Eq. 3-42, is specified to reduce the value to a more correct, realistic level.   Equation 3-42 is specifed as: Note that the value of the exponent is indicated to be -(1/2fc).  I have discovered that, prior to release of the 2nd Edition of ASCE 113, these same equations were presented in IEEE 605 (both IEEE 605-2008 and IEEE 605-2023).  In these documents, however, the Decrement Factor is specified as:

Note that, in this equation, the value of the exponent is   -1/(2fTa), rather than -(1/2fc).  The definition of Ta in IEEE 605 is exactly the same as the definition of c in ASCE 113 (a Time Constant).  The key difference is that all three terms (2, f, and Ta) of the IEEE Equation are in the denominator of the exponent whereas in the ASCE 113 equation, the (f and c) terms appear to be in the numerator.  I am reasonably certain that the IEEE Equation is correct but have come across real world instances where the equation was being interpreted the other way by engineers.  There is a very significant difference in the calculated value of the Short Circuit Force.  If anyone has any additional information or knowledge regarding this I would appreciate your input.  Thanks in advance.