While working on calculation the effects of short-circuit currents according to standard 60865, I came across two cases that were insufficiently solved in the standard but occur very often in my work.
1) Practically vertical droppers that do not meet the condition of 1.4w<lv<3.3w (point 6.3 of standard 60865). I often see 15 m - 50 ft long droppers running down to transformers etc. Cigre 105 says in section 3.3 "If the droppers are stretched, a high loading can occur. Until now a simplified method for the calculation of this force is not available". How to approach it? FEM analysis (what environment)? On this forum I once came across a tip to treat it as a horizontal connection, but if it were that simple I think that it would be written in CIGRE 105. Additional question - if the air terminal is attached at the top to a loose wire at a large distance from the insulator string, should it be considered a threat at all?
2) Short spans with bundled conductors. In my opinion, the standard does not take into account the conductor's own stiffness in the calculations and for short spans the pitch force results are significantly overestimated.
In IEEE Std 605TM-2008 point 11.3.5.1 writes about it directly:
"These methods are valid for spans that are long enough so that flexural conductor stiffness does not play a significant role, which is generally 10–15 m and over. They do not apply to flexible buses interconnecting substation equipment over short spans (generally below 7–8 m; e.g., between a disconnect switch and a circuit breaker).
How to approach this? I can't find it now, but I think I found it in one study from Canada that bringing the spacers closer to a distance smaller than the X times the diameter of the conductor solves the problem.
Similiar issue appended here:
1) Practically vertical droppers that do not meet the condition of 1.4w<lv<3.3w (point 6.3 of standard 60865). I often see 15 m - 50 ft long droppers running down to transformers etc. Cigre 105 says in section 3.3 "If the droppers are stretched, a high loading can occur. Until now a simplified method for the calculation of this force is not available". How to approach it? FEM analysis (what environment)? On this forum I once came across a tip to treat it as a horizontal connection, but if it were that simple I think that it would be written in CIGRE 105. Additional question - if the air terminal is attached at the top to a loose wire at a large distance from the insulator string, should it be considered a threat at all?
2) Short spans with bundled conductors. In my opinion, the standard does not take into account the conductor's own stiffness in the calculations and for short spans the pitch force results are significantly overestimated.
In IEEE Std 605TM-2008 point 11.3.5.1 writes about it directly:
"These methods are valid for spans that are long enough so that flexural conductor stiffness does not play a significant role, which is generally 10–15 m and over. They do not apply to flexible buses interconnecting substation equipment over short spans (generally below 7–8 m; e.g., between a disconnect switch and a circuit breaker).
How to approach this? I can't find it now, but I think I found it in one study from Canada that bringing the spacers closer to a distance smaller than the X times the diameter of the conductor solves the problem.
Similiar issue appended here:
