Wis. Admin. Code Public Service Commission PSC 114.250
If no portion of a structure or its supported facilities exceeds 18 m (60 ft) above ground or water level, the provision of the rule are not required, except as specified in Rule 261A1c, 261A2e, or 261A3d. Where a structure or its supported facilities exceeds 18 m (60 ft) above ground or water level, the structure and its supported facilities shall be designed to withstand the extreme wind load associated with the Base Wind Speed as specified by NESC Figure 250-2(b). The wind pressures calculated shall be applied to the entire structure and supported facilities without ice.
The following formula shall be used to calculate wind load.
Load in Newton = 0.613 " (V m/s) 2 " k Z " G RF " I " C d " A(m 2)
Load in pounds = 0.00256 " (V mi/h) 2 " k Z " G RF " I " C d " A(ft 2)
Where: -
| 0.613 | Ambient Air Density Value, reflects the mass |
| 0.00256 | density of air for the standard atmosphere, i.e., temperature of 15ºC (59ºF) and average sea level pressure of 760 mm (29.92 in) ofmercury. (No adjustment in the velocity topressure coefficient has been made relative tochanges in air density with altitude.) The dimensions associated with this coefficient are, for metric, 0.613 NÌs2/m4; and, for English, 0.00256 lbÌhr2/mi2Ìft2. |
| kZ | Velocity-Pressure Exposure Coefficient, asdefined in Table PSC 114-250-2 |
| V | Basic wind speed, from NESC 250C, Figure250-2 given in m/s at 10 m (mi/h at 33 ft)above ground |
| GRF | Gust Response Factor, as defined in TablePSC 114-250-2 |
| I | Importance factor equal to 1.0 for utilitystructures and their supported facilities |
| Cd | Shape Factor as defined as defined in NESCRule 252B |
| A | Projected wind area, m2 (ft2) |
Table PSC 114.250 -2 (Metric) Velocity Pressure Exposure Coefficient, kZ Gust Response Factor, GRF
kZ. GRF | ||
For Structures: | For Wires: | |
For structures with a total height of 30 m or less above ground or water level | 1.0 | 0.85 |
For structures with a total height exceeding 30 m above ground or water level | 0.93+0.00245(h) | 0.78+0.00245(h) |
Table PSC 114.250 -2 (English) Velocity Pressure Exposure Coefficient, kZ Gust Response Factor, GRF
kZ . GRF | ||
For Structures: | For Wires: | |
For structures with a total height of 100 ft or less above ground or water level | 1.0 | 0.85 |
For structures with a total height exceeding 100 ft above ground or water level | 0.93+0.00075(h) | 0.78+0.00075(h) |
Where:
h = height of the structure above ground or water level. For wind loads on wires attached to the structure, the height of the highest wire attachment above ground or water level may be used if less than the height of the structure. In unique terrain where the height of the wire above ground at mid-span may be substantially higher than at the attachment point, engineering judgment may be used to determine an appropriate value the height of the wire.
Note 2: The height of all wire attachments should be based on the height of the highest attachment or total structure height. The formulas to determine k ZG RF were based on this premise, not the height of each attachment.
The wind pressure parameters (kZ, V, and GRF) are based on open terrain with scattered obstructions (Exposure Category C as defined in ASCE 7-98). Exposure Category C is the basis of the NESC extreme wind criteria. Topographic features such as ridges, hills, and escarpments may increase the wind loads on site-specific structures.A topographic Factor, kzt, from ASCE7-98 may be used to account for these special cases.
Each supply line designed to operate at 300 kV phase to phase or above shall be constructed to limit the effects of a cascading-type failure to a line segment not exceeding 9.6 km (6 mi) to 16 km (10 mi) in length. Such construction requirement may be met by providing, at appropriate intervals, structures and associated facilities having full dead-end capability under the loading provisions of Rules 250 A, B, C and D. Consideration shall be given to factors such as structure type and material, length of line, distance between dead-end or heavy angle structures, and other basic design criteria in determining the length of such individual line segments. For lines supported by "flexible" structures designed with plastic, energy-absorbing capability in failure, this requirement may be met if such design and construction will provide equivalent limitation to longitudinal cascading.
Wis. Admin. Code Public Service Commission PSC 114.250