Developing new and existing electrical systems - the challenges in the standardisation of overhead line designs

摘要

As a country's transmission infrastructure is developed and expanded over time, it is inevitable that the applicable design standards and transmission line design philosophy will develop and mature. When upgrading an existing transmission line, one has to consider if the uprated line will be recommissioned to modern design standards or whether the tower design should be left unchanged if its service performance has been satisfactory. However design obsolescence through advancements in design standards and knowledge have to be considered, particularly where the gap between old and new design requirements is large. The issue of mismatching design standards or variance in reliability level is even more acute on the African Continent as many countries have tended to expand their grid via individual projects. The combination of foreign design consultants and Engineering, Procurement & Construction (EPC) Contractors has led to the use of different design approaches which more often than not reflect the region/country of origin of the engineering consultant rather than being tailored to the terrain and environment through which the line passes. In the long term the varying reliability and maintenance requirements can place additional burdens on the utility and hamper the level of interconnection with neighbouring countries. This paper outlines the challenges that utilities face in seeking to develop both new and existing infrastructure in the context of the aforementioned design standardisation complexities. For new overhead line builds, the paper will discuss the potential difficulties in seeking to build new lines to modern design codes in which local technical resources and knowledge play a key role and which can potentially add significantly to the overall programme costs. For the development of existing overhead line infrastructure, the paper will examine the dependence on as-built information and condition assessment as well as knowledge/records of the design code applied at the time in order to ascertain the "design gap". Two cases studies are then presented, one on new builds and one on the upgrading of existing infrastructure. The first case study is based on a new 132 kV line build in Sub-Saharan Arica The second case study draws on Ireland's experience in seeking to arrive at a process whereby existing lines can be assessed and the appropriate design criteria applied.