Charting the 4-second data following trip of Callide C3 and C4

Following Simultaneous with trip of Callide C3 and C4 (frequency impacts … a first look) we take a further glance.

In this article we align the output of the two units with system frequency.

The chart below captures the drop to 49.866 Hz (within the NOFB of 49.85) that is coincident with both units tripping to from 400 MW to 0MW.

We also note there was a subsequent decline in the following 5 minutes, to 49.831 Hz.

CPP_3 and CPP_4 trip and associated frequency. Source: AEMO data from Global-Roam hosted MMS. 

The chart above shows unit output was 0MW after the trip, near 17:55,

16:55:12 in the AEMO data, in general agreement with 16:55:21 from the Global-Roam logger.

Yet frequency continued to decline over the next 5 minutes..

This timeframe, going by the measurement datetimes, aligns with dispatch settings:

• The trip happened at just after 16:55, therefore at the beginning of the 17:00 interval.
  • Raise responses from FCAS-enabled providers and primary frequency response would have been key to counterbalance supply.
  • A sustained response would have been needed throughout the interval, until the dispatch system set new unit targets.
• Re-dispatch wasn’t until 17:00 for the 17:05 interval.
• Targets sent to units soon after 17:00 (~20 seconds after?) .
• The arrest to frequency decline at 24 seconds into the interval aligns with experience that new unit targets had been received and unit ramping to new targets was supporting the frequency correction from that point.

The frequency nadir of 49.831, uncovered above at 17:00:24, aligns with this chart provided to us by Watt Clarity reader Ben (thank you):

Chart of frequency recorded by a reader’s SolarEdge inverter feeding live data to Home Assistant.