IEEE 605-1998 Equation Error?

[BlownUp]

I have questions about a couple of the equations in IEEE 605-1998 and was hoping someone here might be able to shed a bit of light. In section 11.1 where they calculate bus deflection there seems to be an error in some of the equations. For discussion purposes I will look at equation 14 and 15. Equation 14 calculates bus length using the maximum allowable deflection. The equation matches what I find for uniform beam loading using metric units. For this equation they list a factor “C” of 1.78 for Metric and 1.86 for English units. I think I understand where these two values come from but am not sure about the remainder of the equation staying the same. I am not familiar with how this equation is derived so I am not completely comfortable with the value of 384 being the same for Metric and English units. This is the first issue I have with these equations. So far not been able to find the cross sectional moment of inertia for aluminum bus in metric units I may try converting it and see if the formula works for both Metric and English units.

Equation 15 modifies this to calculate bus length based on a maximum bus deflection ratio. It is followed with a statement to use the previously defined variables. This is the second issue I have with the equation. I don’t think the “C” value should be the same and this is the second issue I have with these equations. In equation 14 the “C” value of 1.78 is the fourth root of 10. The value 1.86 is the fourth root of 12. In equation 15 it looks like they have factored one of the values through and come up with a cubed root formula. I am thinking the values for “C” should then be the cubed root of 10 (2.154) and the cubed root of 12 (2.289).

So I guess I have two questions for folks more familiar with beam deflection calculations:
1. Is the equation really the same for Metric and English units?
2. Should be factors for “C” in equation 15 be cubed roots rather fourth roots?

 

[zumhakr]

Yes ! The 605 1998 is notorious for those constant conversion issues. The new version (605 2008/2010) seems to be consistent so I would suggest using that one.

 

[BlownUp]

Thanks zumhakr,

I ordered the new version and yes it does correct this by doing away with the "C" value and using bus mass in per centimeters or per inch units rather than meters and feet.

Now I get to spend an afternoon going through the new version to see what all else is different. That will be exciting!!

 

[burnt2x]

There is an errata on that IEEE 605-1998 in page 16, 17, 25, 29 and 30. Try google "Corrections to IEEE Guide for Design of Substation Rigid-Bus Structure".