Attachment A - Major Event Day threshold calculation

The AER has shared a Major Event Day threshold calculation workbook. The workbook illustrates how the Major Event Day threshold can be calculated in line with the 2.5 Beta methodology set out in Appendix D of the STPIS, noting a DNSP may propose an alternate methodology in accordance with clause 2.2 of the STPIS.

On 7 January 2025, AER updated the formula in the Ln(SAIDI) column on advice from CPU. This change will return a null value for Ln(SAIDI) when daily SAIDI is zero as intended by STPIS v2.0.

The AER's S-factor calculation model is intended to be used as a tool to help DNSPs understand how the AER calculates S-factors. The model is not a data submission tool but DNSPs can use the model to replicate the AER’s S-factor calculations and test outcomes.

The handbook has been prepared to assist DNSPs identify the input data used in the model, follow the model’s calculation process and interpret the output from the model. It also details the limitations of the model.

The handbook and the model do not replace the AER’s STPIS for electricity distribution network service providers version 2.0 (the scheme V2.0) and if there are any differences between the model and the scheme, the scheme takes precedence. In particular, the model does not cover all the possible scenarios laid out in the scheme. The likelihood of some of these scenarios occurring is low, and attempting to cover all contingencies would increase the complexity—and decrease the accessibility—of the model.