Love Hertz

The last few weeks has seen a flurry of activity in the policy reform space with the release of Dr Finkel’s Review into the Future Security of the NEM, as well as the final report for the AEMC’s System Security Frameworks Review.

Both reviews have emphasised the importance of system security and the management of frequency. Given that we spend most of our time focussing on MWh, this week we thought we would pay some attention to the oft-forgotten heartbeat of the power system: frequency.

Chart 1: 4-second frequency deviation data for the mainland

From our perspective, we are interested in times when frequency deviates from its nominal level of 50 Hz. We are particularly interested in times when frequency wanders outside of the normal operating frequency band of 49.85 Hz to 50.15 Hz. Chart 1 shows the deviation from the nominal frequency (usually 50 Hz) for the NEM mainland system. The data is shown on a 4-second basis for the whole of 2016.

Each point falls into one of the following three categories:

  • Deviations of <= ± 0.15 Hz, ie, within the normal frequency operating band of 49.85 Hz to 50.15 Hz.
  • Deviations between > ± 0.15 Hz and <= ± 0.25 Hz, ie, within the normal operating frequency excursion band of 49.75 Hz to 50.25 Hz.
  • Deviations in excess of ± 0.25 Hz, ie, outside the normal operating frequency excursion band.

You can see that frequency regularly wanders outside of the normal operating band, most often falling below 49.85 Hz.

Chart 1 – Deviation from nominal frequency for the NEM mainland system (1 January 2016 to 31 December 2016)


Chart 2: Historical occurrence of frequency excursions

So how often do these excursions occur? Chart 2 shows the duration of deviations outside of the normal frequency operating band from 1 April 2013 to 31 March 2017. We have coloured the chart according to the extent of the deviation so that larger deviations are indicated in darker colours.

You can see that in 2013 and 2014, frequency excursions were rare. But there has been an inexorable rise in these excursions over the last few years. In March 2017, frequency was outside of the normal operating band for over 4 hours.

Chart 2 – Monthly duration of frequency excursions for the NEM mainland system (1 April 2013 to 31 March 2017)

My two cents

  • Something profound is happening to the power system. If frequency is regularly wandering outside of its normal operational boundaries, this should be cause for concern.
  • In preparing these charts, I have realised how focussed we are in the NEM on energy. Analysts such as myself are perhaps too focussed on MWh, and pay far less attention to other power system outcomes such as frequency.

As always, all comments are most welcome.