The South West Interconnected System (SWIS) is the electricity system which connects Perth with the south west region of Western Australia. It is the second major electricity system in Australia after the National Electricity Market. The generators, poles and wires are largely owned by the Western Australian Government. The SWIS has a Wholesale Electricity Market known as the WEM. Residential customers do not have the same choices as on the east coast of Australia (in the NEM) because the SWIS is not fully deregulated. Western Power operates the poles and wires. Synergy is the retailer and owns some of the generators. Both are owned by the WA Government.

https://aemo.com.au/learn/energy-explained/energy-101/how-the-wholesale-electricity-market-works https://en.wikipedia.org/wiki/South_West_Interconnected_System