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MHI agrees with AEMO’s explanation of the events that led to the black system.MHI agrees that the event was triggered due to lack of inertia on the SouthAustralian side once the Haywood interconnector tripped.
The system inertia on the SA side was not sufficient to maintain thefrequency drop (once the Haywood interconnector tripped) and to make theunder frequency load shedding (UFLS) effective.
As systems lose inertia due to the retirement/displacement of thermal plants andthe expansion of wind farms, frequency control becomes more important, asfrequency control is directly related to inertia. This report was very wise to notethe relatively low level of inertia during this disturbance. The whole topic offrequency control and RoCoF should be examined on a system-wide basis, and alldevices that protect frequency should be reviewed for their appropriateness.
Based on the high impact of low frequency, low voltage, and growing phase anglethreat due to mixed generations (wind, solar, thermal, etc.) over a wide area of theSA network, it is worth considering the real time WAMS (wide area monitoringsystems) using synchrophasors (Phasor Measurement Units - PMUs). Real timewider area early warning systems can be established with the PMUs to cope with the electrical data, such as phase angle stress, voltage stress, and Var phase angleplot.
last of inertia... wind farms dont provide inertia