System Strength Impact Assessment Guidelines

AEMO sees system strength as the ability of the power system to maintain and control the voltage waveform at any given location in the power system, both during steady state operation and following a disturbance.

The System Strength Impact Assessment Guidelines (SSIAG) are made under clause 4.6.6 of the National Electricity Rules (NER). The key function of the SSIAG is to prescribe how connecting Network Service Providers (NSPs) will assess the impact of a connection to system strength when processing connection enquiries, applications for connection or alterations to plant.

The SSIAG covers the following matters, as specified in NER 4.6.6(a) and (b):

• A methodology for undertaking system strength impact assessments, including a preliminary assessment and a full assessment.
• A methodology for calculating a system strength locational factor (SSLF).
• A threshold below which a system strength impact may be disregarded for the purposes of NER 5.3.4B(f)(3) (Materiality Threshold).
• A definition and guidance on the calculation of available fault levels (AFLs).
• A methodology for assessing the short circuit ratio (SCR) for the purposes of the SCR access standards.
• Guidance on information to demonstrate compliance with relevant performance standards.
• The criteria for classification of a load as an inverter-based load (IBL).
• The criteria for classification of an inverter-based resource (IBR) as a large inverter based resource (LIBR).
• How AEMO assesses adverse system strength impacts.
• Guidance on the methodology to be used when undertaking modelling to verify the stability of plant.

Additional information on system strength can be found at the following: