ACST (Australian Central Standard Time) is one of the well-known names of UTC+9:30 time zone which is 9:30h. ahead of UTC (Coordinated Universal Time).The time offset from UTC can be written as +09:30.
It's used during the winter. During the summer ACDT - Australian Central Daylight Savings Time (UTC+10:30) is in use.
Some locations use ACST all year long.