In the NEM, the Normal Operating Frequency Band (NOFB) is the acceptable range of frequency under regular conditions and it is currently set at between 49.85Hz and 50.15Hz.
If frequency strays too far outside of the range for too long, generators and other equipment may start disconnecting from the system in order to protect themselves against damage, which can then start a cascading effect, further causing system insecurity.
During large unexpected events (e.g. the trip of an interconnector..), contingency mechanisms and other emergency schemes are used to arrest the variation and return the power system back to a safe operating frequency as quickly as possible while attempting to minimise consumer impact.
Will add more later…
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