IEC61850 has now been accepted ‘almost unequivocally’ as a preferred standard for substation communications.The extent of utilisation of this standard in a majority of installations around the world is at the ‘station bus’ level. It is foreseen that numerous benefits can be availed if the process values are digitised as close to the source as possible and utilised in a comprehensive automation system. TransGrid carried out an extensive assessment of the substation secondary system design based on the implementation of IEC61850 at the station and process bus level which brought out the business case for full digitisation. The first substation to realise this technology is the Avon 330 kV switching station. At Avon, merging units are installed in outdoor cubicles; digitised signals are then transferred to the substation systems. There has been a special focus on standardisation and re-usable engineering – these are some of the crucial factors to achieve cost reduction. The study describes some of the design principles, estimated cost savings and lessons learnt. The authors envisage that the digital substation technology implemented can bring about substantial cost reduction in green-field as well as brown field builds and paves the way for the efficient integration of asset monitoring systems.