Australian network stabilises renewables using synchronous condensers

Siemens synchronous condenser

ElectraNet in South Australia installs a traditional solution to help maintain network stability on the path to a sustainable grid.

The synchronous condenser is far from an innovative concept but has found a place in maintaining a reliable power supply as Australia transitions towards a highly sustainable, low carbon energy future network. The art of managing a power network lies in the balancing of supply and demand as load varies across the day. Traditional networks source energy from rotating machines such as steam or gas turbine generators. Their rotating mass provides inertia which helps to keep the network voltage and frequency stable if the supply and demand relationship fluctuates more rapidly.

Energy sources such as wind turbines and solar arrays contain much less rotating mass and therefore contribute much less inertia to the network. These rapidly proliferating forms of renewable energy are also inherently intermittent in energy supply as wind varies or clouds pass overhead. Such fluctuations in supply can adversely affect the stability of the network. Overall, as the percentage of renewables increases, the network sees more short-term intermittency but has less inertia to maintain stability.

South Australia is leading the change in Australia, and indeed the world. It has a significant penetration of renewable energy sources, including up to half of Australia’s wind energy and a third of its solar, and has plans for continued growth. As the aged fleet of coal-fired plant is successively decommissioned and replaced with distributed renewables, AEMO, the Australian Energy Market Operator, has recognised the need to address potentially decreasing network stability. In terms of relatively short-term responses, some large battery energy storage solutions have been connected which provide fast response Frequency Control Ancillary Services (FCAS) in the South Australian grid. The Australian Energy Regulator has approved ElectraNet’s application to install four synchronous condensers within the network to further bolster stability. In order to increase the effectiveness of the system, the rotating mass of these machines is enhanced by the addition of flywheels.

The first two condensers will be sited in Davenport, near Port Augusta, and are scheduled to come online in April 2021. Two further condensers will be sited in Robertstown, near Adelaide.

 

A condensed solution

Synchronous condensers are parallel connected rotating machines which can be placed at critical points within the network to provide similar stability to traditional generators, helping to stabilise system frequency through the addition of inertia. Controlling the excitation field strength allows the machine to appear as either a large capacitor or reactor to the network, thereby allowing system Vars to be either injected or consumed, as required and thus providing voltage stability for the network.

The addition of synchronous condensers has enabled ElectraNet to quickly add an effective device to help stabilise both voltage and frequency on the network. It is expected that the addition of more storage solutions, such as rapidly improving battery energy storage systems and pumped hydro where conditions are suitable, will add the firming required to facilitate the continued transition to a more decarbonised, more sustainable energy profile. Longer term, an additional transmission interconnector is in the pipeline to connect to the NSW grid, adding stability and facilitating the connection of additional large-scale renewable plant. Australia is on track to meet its carbon reduction targets in the electricity network, supporting the journey toward a zero carbon, highly sustainable electricity grid.

Carbon reduction targets in transportation will require additional work to facilitate the large-scale uptake of electric vehicles. This will place more demand and variability on the grid and be likely to require additional sustainable energy sources along with network stabilising capability.

 

Image: Siemens synchronous condenser