Introduction: 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 project output will also better inform the wider industry, allowing DNOs to optimise their designs to avoid such problems. 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.

Objectives:

The aims of the project are:

• Improve the knowledge of current flows and the earthing contribution from a nearby or surrounding network in terms of a global earthing system.
• Identify the tangible benefits and application of global earthing systems including the potential to reduce (or optimise) the cost of substation earthing.
• Trial various methods to ‘decouple’ the local substation earthing system from the overall combined network earthing system.
• Develop a revised methodology and/or set of parameters to update UK Power Networks’ substation earthing design tool and earthing design standards.
• Produce an interactive training package on how to use the revised process.
• Publish a paper on the work undertaken to inform others and (via ENA or other forums) share amongst GB DNOs
   

Expected Benefits: The project will be deemed successful if:

• The learning outcomes defined in “Objectives” are achieved.

• It can be shown that less earthing is required at distribution substations, when comparing the new substation earthing design tool with existing methods on a sample of sites.