A lot of distribution substation earthing design is standardised by utilities and can be completed in a relatively routine manner, but occasionally scenarios appear which do not easily fit the standard design mould and needs the attention of an experienced earthing engineer.
This presentation will cover two such scenarios which are becoming more common in Tasmania. The first is a temporary HV embedded generator site which was established to provide supply to a rural township, the โtrickyโ element being the proposed siteโs location being on customer land near a residence and MEN stakes. The second is a typical distribution design conundrum: the โsmall industrial customerโ supply substation, where a small isolated site requires a ground mounted supply and the designer must work through the decision of separate vs common earthed configurations, whilst keeping the site as safe as possible in the long term.
There are many lessons to extract from such scenarios, such as:
โข The difference in how we apply safety criteria in the scenarios of temporary vs permanent installations;
โข The design assumptions that are required in estimating the expected MEN system performance and how they can vary (wildly) in practice;
โข Factors external to the immediately technical aspects of a design that affect it, like time pressures, assumptions behind customer behaviour, and long term asset management considerations; and
โข Considerations for Systems and Standards: Where these scenarios could have ended badly if the design process had missed or skipped certain steps, an unfortunate but real risk within a utility context.