IEC Guide 111-1:2023 is a horizontal publication which gives guidance for the harmonization of product and system standards for HV substations (higher than 1 kV). It addresses AC equipment which is found in high-voltage (HV) substations in most cases.
This document contains recommendations for common specifications for all HV substation product and system standards, each of which is augmented by the technical background specific to each technical committee, which naturally retains freedom in its technical choices.
This document is applicable when developing product and systems standards for HV power electronic equipment for the AC part of the substation.
This first edition of IEC Guide 111-1, together with IEC Guide 111-2, cancels and replaces the second edition of IEC Guide 111 published in 2004.
The main changes with respect to the previous edition are as follows:

1. IEC Guide 111 is revised into two parts – Part 1 for AC and Part 2 for DC (Part 2 to be prepared);
2. the scope of the document has been expanded to cover electric equipment in AC high-voltage substations;
3. new definitions have been included;
4. normal conditions have been revised;
5. a general revision of other clauses.