5.1 Historical review

Throughout the twentieth century electricity became arguably the most important commodity provided to the home and industry and now interacts with almost every aspect of our lifestyle. Distribution overhead line designs supplying electricity up to 33 kV, unlike electrical goods, have not necessarily changed all that much, yet there have been significant developments in design criteria that should be noted. Overhead line reliability and safety have been heavily criticised in recent years and so there is a need to address the issues of future overhead line design. This chapter looks at some of the fundamental steps that are adopted in developing a new overhead line wood pole design for the UK environment together with some historical references and the effects of new European legislation.

5.2 Background

A detailed review of design standards is given in chapter 2 from a regulatory viewpoint. In this section the relevant standards are considered from a design viewpoint.

Regulation 15 of the Electricity Supply Regulations (1937) stated overhead lines shall be erected and maintained in accordance with the provisions of any regulations made under the Electricity Supply Act 1882 1936 . The regulations specifically applying at that time were the Overhead Line Regulations of 1931 which, for all lines above 325 V, laid down the following design standards:

Conductors factor of safety 2.0 on the design conditions of wind pressure of 8 lbs/sq ft acting on 3/8 ? radial ice-loaded conductor at 22 F.

Wood poles factor of safety of 3.5 with wind pressure of...