Power System Oscillations

West Murray Zone Intermittent Power System Oscillations

The West Murray Zone (WMZ) is an area of the National Electricity Market (NEM) with low system strength, extending across parts of Victoria and New South Wales. This area has attracted significant investment in grid-scale solar and wind generation in recent years. 

The WMZ continues to pose operational challenges for AEMO, Network Service Providers and Generator Developers following power system oscillations observed in 2019. The nature, extent and causes of these issues only become apparent with the advanced and detailed modelling capability that is now essential for technical assessments in weak areas of the grid. Further information on the WMZ can be found on the Connections in Low System Strength Zones webpage.

AEMO has observed intermittent power system oscillations in the West Murray area (VIC/NSW) under a variety of conditions since first identified on 20 August 2020, following a line trip in the WMZ.

Soon after the event AEMO developed a bespoke tool that monitors high resolution power system quantities at Red Cliffs Terminal Station (RCTS) 220 kV and captures intervals with sub-synchronous voltage oscillations.

The frequency of oscillations has been around 19 Hz with varying magnitude. While analysing number of instances when power system oscillations were observed the highest magnitude of oscillations has been closer to the Red Cliffs area. 

On 25 August 2021, AEMO held an industry briefing where we presented information regarding a number of instances of these oscillations. Subsequent to that AEMO also released sample oscillations data for stakeholders to analyse.  

AEMO is working closely with AusNet, Powercor and relevant participants to resolve the issue. AusNet installed additional CT-Labs1 monitoring equipment at Wemen area which is helping the investigation. Powercor has now installed similar monitoring equipment in their sub-transmission network under Wemen Terminal Station to further support the investigation.  

AEMO has worked in collaboration with AusNet and Powercor to develop a report that provides further information on the observed intermittent power system oscillations, published in October 2022: High level summary of WMZ – Subsynchronous Oscillations.

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