Koi Koi Grace
by on March 5, 2019

The design of transmission line structures involves both analysis of the structural system – wires, supports and foundations – as well as design checks ensuring compliance with established norms and guidelines. Worldwide, most countries have institutions and standards devoted to design, construction and safe operation of utility structures. These standards or codes cover a variety of parameters such as loading, conductors, materials (steel, wood and concrete), hardware, clearances, performance and other issues relevant to the system. Table 2.19 shows a selected, partial listing of some of the codes, manuals and design standards used in various countries. As mentioned in the Preface, the basic principles of transmission line structural analysis are more or less the same all over the world; but different regions impose different rules and regulations, mostly associated with their local experience, climate, economy and safety and reliability requirements. Despite that, these codes and standards have a universal purpose: to ensure that transmission structures and foundations are designed for safe and reliable operation during their lifetime.

As mentioned in the previous chapter, transmission line and structure design in United States is primarily governed by the NESC supported by RUS Bulletin 200 in various ways. It must be noted that the NESC is primarily a safety code which is not intended as a design specification or an instruction manual. Along with many other standards noted in the text at various locations, the above two references constitute the main sources of design guidelines discussed in this book.



P2.1 Determine adequate ROW for a 230 kV line for the following data. Horizontal distance between insulators = 28 ft (8.53 m) Suspension Insulator Length = 8 ft (2.44 m) Sag at 60◦F at 6 psf (290 Pa) wind = 10 ft (3.05 m) The swing angle of the insulator under 6 psf wind = 45◦ The required C per internal standards = 13 ft (3.96 m) away. Neglect pole deflections.

P2.2 Re-do the problem in P 2.1 assuming horizontal post insulators. Use A = 14 ft (4.27 m). What is the basic difference between the two cases? Discuss.

P2.3 A tension section of the above 230 kV transmission line contains the following spans: 1020 ft (310.9 m), 1090 ft (332.2 m), 1130 ft (344.4 m) and 1070 ft (326.1 m). Determine the Ruling Span.

P2.4 For a tangent structure in a 138 kV line, assuming maximum conductor sag of 9 ft (2.74 m), determine the minimum height of a pole required if 13% of the total length is used for ground embedment. Assume a ground clearance buffer of 3.5 ft (1.06 m).


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