How long must a substation DC system last on discharge?

Ten hours is the published Australian benchmark. AusNet’s asset management strategy states DC systems “have been designed to maintain DC supply to 10 hours after AC interruption for system black or ZSS black purpose.” For comparison across the utility sector, Sydney Water’s HV installation specification requires a minimum of four hours plus the capacity to complete two full operations of the installation within it, sized by the IEEE 485 method with a 10% design margin and a 25% ageing factor, which is the exact formulation Australian utility specifiers use.