Compact Overhead Line Design

This book provides the design engineer with an understanding of the electrical parameters and methods required in designing compact AC and DC lines. As the need for high voltage direct current (HVDC) links within or overlaying existing AC systems and providing high capacity is more widely recognized, rights of way (ROW) for those lines become increasingly difficult to obtain. The increased urbanisation and demand for power in built up areas has led to increased power requirement in limited corridors. This has led to the need for more compact lines where the same power can be transferred in a narrower right of way. This Green Book explains the concept of DC line compaction for reduced ROW and/or height as well as compact AC overhead lines. By reducing the horizontal distances and heights results in increased electric fields and other effects which may become the limiting factor and are necessary to manage in the design of a compact line. Therefore, compacting simply means maximizing the power transmitted on a given ROW cross section or, inversely, minimizing that cross section for a given power transfer requirement. In general, HVDC links are designed to transmit high amount of power over long distances, or to serve as system interconnectors. Both AC and DC lines being utilised as system interconnectors and high power capacity lines, require high levels of reliability and availability. Therefore, aspects like insulation coordination and live maintenance must be kept in mind. These are covered in the Green Book. For DC power lines, increased power flow can only be realised by increasing the current through the conductors and/or increasing line voltage. In AC it can also be done by bundle expansion and phase compaction due to the variation of impedance. So, compaction has not the same effect in AC or DC lines, and the constraints associated with compaction are also different (corona-related effects, clearances, arrangements…). The Green book covers the theory in both AC and DC lines. In addition to the theory, the Green Book includes actual calculations of electric parameters for different pole and phase configurations. Note that the parameters used as limits in the different countries need to be adopted as a whole, because they are interrelated. It is not possible to use one limit from one country and another limit from another in one line design unless the designer is aware of the interaction between the parameters. Case studies on line compaction designs for both AC and DC are described with relation to pole compaction, pole rearrangement and phase configuration. Voltage upgrading is also treated in this book, and some case studies for both AC and DC are considered.