Pacific Hydro exposes a major threat to power system security

Pacific Hydro has identified a significant technical issue with the controls of the large baseload generators in the National Electricity Market (NEM), which could potentially compromise the security and stability of Australia’s electricity grid.

The de-tuning of the baseload synchronous units – which reduced their ability to react quickly to frequency changes – appears to have occurred in response to the introduction of the frequency control market, rule changes, and the gradual alteration of control practices since 2001.

New analysis of the NEM by Pacific Hydro’s electrical engineering team shows significant deterioration of frequency control. Unexpected oscillations (system frequency moving up and down in a regular variation) are occurring, according to publicly available data.

These unstable events may present a significant risk of damage to the baseload synchronous generators.

Pacific Hydro is raising these issues as it important that the frequency control is re-established and the grid stability recovered, to get the best result out of the market for customers, energy users and generators.

The problem was identified during our internal investigation after the SA system black event, and preparation of responses to the Finkel Review and other inquiries. This threat requires an in-depth power system control engineering analysis to be undertaken. The oscillations occur when there are relatively small losses of generation or load. The frequency does not recover adequately and this type of power system behaviour should be avoided.

The NEM is designed to operate at a frequency of 50 Hertz (Hz). Deviation from 50 Hz occurs when power generation and demand are mismatched – too much demand leads to frequency drop, while too much generation leads to frequency rise. A sudden drop in demand or generation also affects frequency (a ‘contingency event’), so quick response to any change is essential for maintaining system stability.

All the parts of the system – from the generators to the electrical devices at the energy users’ end – rely on stable and tight control of frequency. For baseload synchronous generators it is fundamental; without it they may be at risk of loss of synchronism, which could cause catastrophic damage. Unstable frequency can also potentially damage electrical equipment and lead to blackouts.

If a large baseload synchronous unit had a control problem occur during one of these frequency oscillations, the current control system tuning may not be able to dampen or stabilise the situation. Whether hydro, coal- or gas-fired, these generators account for the majority of Australia’s power plants, and there is a real risk that they could suffer consequential damage.

Measurements show that the instability is not caused by asynchronous (wind or solar) generation in any of the identified events. In fact, output from these renewable energy generators remains stable and consistent, and accounts for a fraction of the total active power in the system at these times. Further, asynchronous units do not oscillate with frequency nor are they tightly coupled to it as synchronous baseload units are.

In line with our commitment to good engineering practice, power system stability, and being a responsible energy market participant, Pacific Hydro is raising these issues so that they can be fixed, and is making these findings available in the public interest. We stand ready to assist the Australian Energy Market Operator and all stakeholders, and contribute to a secure and stable power system.


Finkel Review – Pacific Hydro submission

Finkel Review – Pacific Hydro reference material