Dynamic conductor ratings: annealing properties of homogenous conductors across varying climatic conditions

Static line ratings are currently utilised by electrical supply authorities to provide a safe and conservative rating for their overhead network. This in turns provides energy security to the customer and longevity for the conductor. Due to current economic environments, energy supply authorities are starting to consider the implementation of dynamic line ratings (DLRs). The dissertation’s main objective is to analyse the available methodologies for modelling the heat balance equation (HBE) in order to provide Ergon Energy Corporation Limited (EECL) the means to implement dynamic ratings. Research has proven that a DLR exploits the available weather parameters and temperature levels in order to increase or decrease the networks ampacity, hence a DLR is typically established by adjusting the convective losses. This has become an area of interest for EECL as they continue to investigate ways to reduce both their capital and operational expenditure, whilst continuing to be an explorative and innovative company. The initial aim of scrutinising the HBE methodology is to determine which application is most suitable for EECL. This was identified as a critical task as the Australian standard AS/NZS 7000:2010 directs the reader directly to IEC/TR 61597-1995, which is dramatically different to that which is provided by ESAA D(b)5 1988, the currently methodology utilised by EECL. The results of this sensitivity test reiterated that the existing process provided by ESAA D(b)5 is in fact satisfactory as it is more superior to the IEC/TR 61597, hence eliminating EECL from remodelling there ratings process. The completion of the sensitivity analysis returned results that highlighted specific characteristics which can be used to adjust the ampacity of the network. These components are; ambient temperature; wind speed; and wind approach angle. Such knowledge becomes beneficial as EECL has access to the Bureau of Meteorology’s (BOM) historical weather data, for which a statistical analysis can provide a means of predicting the types of weather conditions expected over the duration of the dynamic period. Associated with DLRs is the inherent risk of conductor annealing and increased conductor sag. Understanding the severity of the risks, it has been identified that the lifespan of the conductor was required to be determined. Calculating this is problematic for EECL as there are minimal records of conductor operating temperatures and high temperature exposures. To overcome this problem, a dynamic conductor ratings model was created. This model stipulates that if the current tensile strength of the conductor is unknown, it is to be sampled and tested. The results of this test will provide an expected tensile strength that can be used to back engineer the residual lifespan, hence allowing for the level of risk in a DLR to be quantified. The impact of uprating a conductor with respects to DLRs, as identified in the dissertation, has the potential to provide great financial benefits and more flexibility to the network. It also has the potential to place the asset and community at serious risk. The results and outcomes of this dissertation have the potential to assist plant rating engineers, asset managers and network planners in their understanding and application of DLRs, such that they will be able to identify portions of the network which as safe to uprate and portions which may require de-rating. It is also expected that by highlighting the risks involved, it will encourage EECL to begin monitoring the lifespan of the network, hence allowing them to gain a better knowledge of the life expectancy of a network and its available ampacity