WG B1.47 Implementation of Long AC HV and EHV Cable Systems
Working Group B1.47 chaired by Ken Barber from Australia prepared the recently published Technical Brochure (TB no 680) on Implementation of Long AC HV and EHV Cable Systems. This working group received strong support from Australia, which hosted one of the working group meetings.
It has been specifically prepared with the aim of providing a comprehensive document which it is hoped will be a valuable reference by any Utility, Government agency or Investor looking to put in an underground system. It focuses particularly on what can, or has been done and demonstrates that cables can be used for long AC transmission links despite their capacitive nature.
For example, some ten years ago, considerable effort was needed to convince persons appointed by the Victorian Government that it was indeed very practical to provide an 88 km, 220 kV underground AC cable to supply power to the Desalination plant being established in Victoria.
Today we are seeing many underground and sub-sea cable circuits being established which are 50 – 150 km in length. This TB explains the reasons for this very dramatic change of events and provides guidance in terms of the special factors that must be considered when designing such links.
Firstly, what is meant by a long length circuit? In the document, it is suggested this would be a minimum of 40 km for voltages less than 220 kV and 20 km for 220 kV or greater. With this definition it is interesting to note that for 30 years between 1967 – 1997 the working group could only find 13 such projects world-wide.
However, in the 3 years 2012 - 2015 there were at least 22 projects involving more than 5 times as much cable and this trend is escalating, because of the commercial benefits in having rapid interconnections to the grid. Nowadays many of the offshore wind farms are connected by AC submarine cable rather than using DC systems, due to issues related to space on the offshore platforms, costs, losses, and maintenance.
Why is there now such a significant interest in Long Length AC Power Transmission by insulated cables? Some of these reasons, which are discussed in the TB are as follows: -
The TB demonstrates that it is practical to build AC Cable links for a wide range of power transfer requirements, Currently there are links of more than 150 kms in length and loads of more than 500MVA for up to 100km of length, so we expect to see even longer links in the future.. However, each link is unique and system design modelling needs to confirm practicality and ensure compatibility with the network. It discusses cable and accessory design trends, reactive compensation to offset the cable capacitance, the need for harmonic filtering and most importantly the key factors to consider in terms of reliability of supply.
Technical Brochure 680 is available free to members through the e-cigre document site, non member can buy it for 340€.