BlownUp
Electrical
- Jun 23, 2006
- 18
I am working on a spreadsheet for calculating bus and insulator loads for substations in the US. These calculations are based on IEEE 605-1998 Design Guide for Subsation Rigid-Bus Structures.
I have gotten down into Section 12.1.5 and there is an equation (35) for "total cantilever load acting at end of insulator". In this equation there are two overload factors, K1 for wind forces and K2 for fault current forces.
In Section 12.2 it discusses these factors. For the wind factor it throws out 2.5 as a conservative recommended by some US insulator manufacturers with no other explanation or guidance. For the fault current forces it states 1.0 can be used if some conditions are met or a dynamic study should be performed or a value of 2.5 should be used.
I have done the calculations using 2.5 as the factors but the calculated bus spans come out short (much shorter than I have seen in real-world applications). I was planning to use the calculations in the pre-design stage to develop bus support locations in the substation. Evaluations of the conditions described are not possible at the pre-design stage as the "mounting structure cantilever spring constants" are not available and a dynamic study at this point is also not yet possible. Designing with the 2.5 factors should be "safe" but may also be very costly as bus supports will be located close together. By the time actual data is available to re-evaluate the design will likely be too firm to alter bus support spacing.
Can anyone recommend a good reference for using factors other than the suggested 2.5? I don't mind going back later in the design phase to verify the design based on actual data. What I don't want to do is have to redo the design in a later stage of the design effort. What I am looking for is a safe factor (smaller than 2.5) that will yeild reasonable bus spans that upon later verifiation will meet the requirements virtually all the time.
Any suggestions?
I have gotten down into Section 12.1.5 and there is an equation (35) for "total cantilever load acting at end of insulator". In this equation there are two overload factors, K1 for wind forces and K2 for fault current forces.
In Section 12.2 it discusses these factors. For the wind factor it throws out 2.5 as a conservative recommended by some US insulator manufacturers with no other explanation or guidance. For the fault current forces it states 1.0 can be used if some conditions are met or a dynamic study should be performed or a value of 2.5 should be used.
I have done the calculations using 2.5 as the factors but the calculated bus spans come out short (much shorter than I have seen in real-world applications). I was planning to use the calculations in the pre-design stage to develop bus support locations in the substation. Evaluations of the conditions described are not possible at the pre-design stage as the "mounting structure cantilever spring constants" are not available and a dynamic study at this point is also not yet possible. Designing with the 2.5 factors should be "safe" but may also be very costly as bus supports will be located close together. By the time actual data is available to re-evaluate the design will likely be too firm to alter bus support spacing.
Can anyone recommend a good reference for using factors other than the suggested 2.5? I don't mind going back later in the design phase to verify the design based on actual data. What I don't want to do is have to redo the design in a later stage of the design effort. What I am looking for is a safe factor (smaller than 2.5) that will yeild reasonable bus spans that upon later verifiation will meet the requirements virtually all the time.
Any suggestions?