Major blackouts prompt rethink about frequency control on the grid

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20 December 2019 12:29 PM

Source: Unsplash

The wind industry – or more specifically the software settings on many wind turbines – copped much of the blame for the state-wide blackout in South Australia in September 216. But it was the response, or the lack of it, from some of the state’s biggest gas generators that really worried many energy experts.

Their fears were confirmed in August last year when, on the first day of Scott Morrison’s prime ministership, lightning strikes took out major transmission links between NSW and Queensland, prompting a series of events that caused two states to be “islanded”, tens of thousands of people to lose power, and a realisation that all is not well with the electricity grid.

That incident in August last year became the catalyst of a major rethink about the way frequency control and ancillary services – an incredibly important response to system faults that can more or less decide whether the lights will go out or stay on – is managed in the country’s main grid.

While South Australia sailed through without issues and was the only grid to emerge unscathed in that August event – thanks in part to the quick and versatile response of its big batteries – the Queensland grid was shaken by the failure of many big coal and gas plants to do what had been expected of them, and respond to the frequency changes.

The Australian Energy Market Operator – and many energy experts – say it highlights the need for changes to rules to try and arrest the decline in frequency performance in the NEM, sheeted home to the relaxing, or in some cases, the absence of governor controls in big coal and gas generators.

They pointed to growing concerns that big coal and gas generators had been relaxing their governor controls, and altering their “dead-band” settings to the point where they were not responding to major frequency variations until after they had moved beyond safe operating levels. This was confirmed by the August event in Queensland.

“The lack of PFR (primary frequency response) from some generating systems contributed to significant technical challenges in arresting and controlling power system frequency, particularly in the earlier stages of the event,” AEMO noted of the Queensland event.

Some experts, such as Advisian’s Bruce Miller, describe the lack of frequency control on the main grid as like driving a car with the steering wheel getting looser and looser.

He and others blame the relaxation of settings to the way the market is designed. They say market signals – from 45 different FCAS markets – are taking precedence over the technical requirements of the grid.

“The FCAS markets are not providing the necessary signals to keep the system frequency under control,” he said in a recent presentation at a seminar called to discuss the issue. “The entire system is at risk.”

Miller worked with power engineering expert Peter Sokolowski – and a group of others including Kate Summers, Jack Bryant and Lasantha Meegahapola – to put forward a change in the rules, largely in line with that wished by AEMO, and it appears they have been largely successful.

The major rule-maker, the Australian Energy Market Commission, has relaxed is dogmatic adherence to market signals and accepted an interim proposal to make some sort of frequency response compulsory on all generators.

That idea is not without controversy. The Clean Energy Council, and many renewable energy developers, suggest requiring the entire generation fleet to meet the PFR requirements may be inefficient and a case of “overkill”, when a more targeted method such as direct contracting may be more cost effective interim measure to restoring frequency control.

Battery storage providers, with an eye on the growing FCAS revenue market, and knowing that they are probably best placed to provide the range of PFR – thanks to their speed and versatility, agreed.

In the end, AEMO will be allowed some discretion, and individual generators can negotiate with the market operator. Miller suggests wind and solar farms are going to have to get used to providing PFR (it may require a small dialling down of their output to give them manouvrabililty – if the system is to move to 100 per cent renewables.

Another energy expert, Kate Summers, says that in order to ensure that the power system can withstand events in the future, new renewable plant should in the future provide a dynamic active power response that is sensitive to frequency.

But she notes that some older type 1 and 2 wind turbines may not be able to deliver this service, and should not be required to because their influence on the power system is small. “They must not be unduly penalised for this as it was not a requirement at the time they connected and their influence on the system is small.”

Miller notes that frequency control is effectively free because it is a control function that all generators should be capable of. On the other hand the provision of “reserve” i.e. the ability to respond, is not free because it affects the dispatch of generation and accordingly attracts an operating cost. Battery (or other types of ) storage has a role to play in reducing provision of reserve by generators on the system.

AEMO chief Audrey Zibelman welcomed the changes.

“The changing nature of the power system under-pinning the NEM has resulted in a lack of effective frequency control, which poses risks to system security,” she said in a statement.

“This rule change calls upon capable generation plant, both existing and new, to automatically respond to frequency changes and ensure that power system frequency is adequately controlled. It is a critical step towards improving system resilience and predictability.”

(The AEMC draft decision on FCAS was one of 16 major decisions released by the rule maker on Thursday, along with another dozen or so reports from AEMO and the energy regulator. The normal pre-Xmas rush).

Giles Parkinson

Giles Parkinson is founder and editor of Renew Economy, and is also the founder of One Step Off The Grid and founder/editor of the EV-focused The Driven. He is the co-host of the weekly Energy Insiders Podcast. Giles has been a journalist for 40 years and is a former business and deputy editor of the Australian Financial Review.