The project will carry out measurement and modelling work to enhance our understanding of network behaviour, particularly for urban and village networks, under fault conditions. The project will examine how the presence of a global earthing system can be used more readily in secondary substation earthing design to ensure safety whilst reducing the amount of copper electrode.
What is the project about?
Dense urban cable networks, by their very nature, create difficulties for earthing measurements. Given that earthing design relates directly to the safety of staff and members of the public, it is important to have detailed and accurate measurements to confirm a) that a substation is safe and b) satisfies the requirement established by third party services and utilities with regards to earthing e.g. their metallic fences. In addition to the measurement difficulties, there is also a fundamental lack of understanding in the way that earth fault current flows within an HV interconnected cable network which is also termed a ‘global earthing system’.
Currently, a number of assumptions are made during the earthing design of secondary substations, which err on the side of caution. Consequently, earthing systems may be ‘overdesigned’, i.e. they are more comprehensive than they need be. This leads to inefficiencies both at the design and installation stage, which potentially leads to more copper being installed and excavations being larger than necessary.
The project will research the behaviour of 11kV networks under fault conditions to understand the earth fault current return paths as well as exploring the effect of nearby urban/suburban networks on safety (step and touch) voltages and the concept of the ‘global earthing system’.
How we’re doing it
The project will research the behaviour of 11kV networks under fault conditions to understand the earth fault current return paths as well as exploring the effect of nearby urban/suburban networks on safety (step and touch) voltages and the concept of the ‘global earthing system’.
Accurate knowledge of the network, earth fault current flows and whether a global earthing system applies will be used to optimise the earthing design process. The output will ensure that earthing systems are designed to ensure safety, whilst allowing more efficient use of copper electrodes at secondary distribution substations. It is anticipated this will result in a cost saving (both materials and installation cost) for each new/upgraded substation going forward.
The findings may ultimately be used to inform future updates of industry standards including ENA TS 41-24 and ENA EREC S34. The project will be validated by applying the revised secondary substation earthing design approach developed by the project to a sample of existing projects in recent year(s) that were designed using the UK Power Networks’ existing earthing design approach. The assessment between two approaches will determine the difference on the amount of copper electrodes required.
What makes it innovative
This project is commissioned to undertake further research, measurement and analysis to address the challenges on designing of earthing at secondary substation. This is a technical research project using an innovative approach to improve understanding of how a global earthing system can contribute substation earthing design and the current that flows through the ground when an earth fault occurs.
What we’re learning
Network contribution – improved understanding of how a global earthing system can contribute to substation earthing system design and the contribution that can be included from dense urban areas, small towns/villages global earthing system and sparser rural networks.
Fault current distribution – the current that flows through the ground when an earth fault occurs when the substation is supplied completely by underground cable or overhead line is easily calculated using standard formulae.
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