A history of synchronous condensers in Victoria

In the past decade wind and solar generation has been displacing older coal fired power stations in Australia, with the stability of the electricity grid coming into question. One of the proposed solutions is something called a synchronous condenser – a technology that the State Electricity Commission of Victoria took advantage of fifty years ago.

Codrington Wind Farm

So what am I even on about?

ABC News looked into the topic of grid stability back in 2017.

Power grids are complex machines, dependent on the laws of physics. The national grid is designed to operate at a consistent frequency of 50 Hertz, or 50 cycles a second.

Traditional coal, gas and hydro power stations are considered “synchronous” because they use turbines or spinning wheels to produce electricity. Those spinning parts need to stay close to 50Hz to help keep the grid in synch.

But most of Australia’s installed wind and solar systems are not considered to be. That’s because they use inverters to connect to the grid, rather than spinning wheels.

If too much power is fed in relative to demand, the frequency will increase. If demand outstrips supply, the frequency drops. Regulators rely on a suite of technologies to help keep the grid frequency close to 50Hz.

Synchronous condensers are one of the technologies used to maintain the frequency of the grid, with Energy Networks Australia explaining the technical details in their piece, The age of the syncons.

What is system strength?

System strength is important as it relates to the ability of the power system to withstand changes in supply or demand while maintaining stable voltage levels.

When system strength is low, generators may not be able to remain connected to the grid, control of the power system voltage level becomes more difficult and protection systems (which control and maintain the safe operation of the network) may not operate correctly. This can result in supply interruptions to customers.

System strength is typically provided by synchronous generation such as coal or gas-fired generation or pumped hydro.

What are synchronous condensers?

Synchronous condensers are an old technology, commonly used as far back as the 1950s to stabilise power systems.

They are large machines which spin freely and can absorb or produce reactive (Alternating Current – AC) power in order to stabilise and strengthen a power system.

Synchronous condensers help when there are changes in load as they increase network inertia. The kinetic energy stored in a synchronous condenser contributes to the total inertia of the power system and is beneficial from a frequency control perspective.

What is inertia?

Inertia in the energy system refers to the continuous momentum of energy typically provided by the large spinning turbines of synchronous generators like large coal-or gas-fired power stations. This type of generation helps withstand changes in generation output and load levels to keep the system stable.

The retirement of synchronous power plants and more renewable generation coming into the energy system means there is less inertia available, so flexibility or stability must be found elsewhere in the system to back it up.

And their usage in Victoria

Until the 1990s the electricity network in Victoria was managed by a single government entity – the State Electricity Commission of Victoria.

State Electricity Commission of Victoria warning sign

Brown coal from the Latrobe Valley was their fuel of choice.

Hazelwood Power Station - 1960s chic

But despite all of the old fashioned spinning metal in their power stations, in 1966 the SECV installed a 750 rpm +125 -75 MVar at 22 kV capacity synchronous condenser at the Templestowe Terminal Station in north-east Melbourne.

A few years later a second synchronous condenser was installed at the Fishermans Bend Terminal Station, south of the Melbourne CBD.

Looking down on the Bolte Bridge and Yarra River

And in 1971 a third unit at Brooklyn Terminal Station, in Melbourne’s west, with a salient pole design rotating at 750 rpm, with a rating of +110 -64 MVar at 14.5 kV, and a short time overload rating of 140 MvAr (10 min).

Front gate to the electrical substation

Following privatisation the reliability of the synchronous condensers declined, with availability falling below the 91% target in 2003. As a result network operator SP AusNet launched a refurbishment program to address degradation of stator winding sidewall and rotor pole insulation, but by 2013 only the unit was Brooklyn had been upgraded.

As a result reliability declined, with the end coming in October 2016.

AusNet Services and AEMO agreed in October 2016 that it was prudent to retire, rather than replace, these three synchronous condensers on the transmission network. These assets were in extremely poor condition and studies confirmed that their replacement would not have provided a net market benefit.

Since the agreement to retire the synchronous condensers, all three units have failed due to their poor condition. Given that the synchronous condensers were due to be retired by 1 April 2017, AusNet Services and AEMO agreed that it was not efficient to repair and return the synchronous condensers into service.

With SP AusNet realising an additional $7.0 million depreciation charge in their 2017 annual report.

Everything old is new again

In 2017 synchronous condensers hit the news, when AGL flagged them as one part of their transition away from coal fired power.

Liddell Power Station is a 2000 MW black coal fired thermal power station, commissioned between 1971-73. The site also includes associated infrastructure required for power generation, including water, coal and transmission plant.

In April 2015 AGL released a revised Greenhouse Gas Policy. The Policy outlined AGL’s commitment to the decarbonisation of our electricity generation portfolio, confirming closure dates for our coal-fired power stations. The announced closure date for Liddell is the end of 2022.

AGL believes that the installed capacity and energy output from Liddell is best replaced with lower emissions and more reliable generation, with a longer lifespan.

As part of our NSW Generation Plan we are investigating the use of one Liddell generating unit as a synchronous condenser.

As part of new solar farm proposals.

Many other wind and solar projects in Victoria and elsewhere are having to go back to the drawing board because of connection requirements the developers either ignored, or didn’t know about.

The issue is most acute in western Victoria, but is also being felt in northern Queensland and south-west NSW.

Many new projects are being told that they face significant curtailment without either adding battery storage or old-style machinery known as synchronous condensers to deal with system strength issues.

Both options are causing headaches for developers, because either way they are trashing their financial models, and could cause extensive delays to projects that many expected would begin construction anytime soon.

As a high cost fix for system flaws.

RenewEconomy has been told that a synchronous condenser could add $8-$10 million in costs to projects already tight on margins. A group of solar farms in north-west Victoria have been told, RenewEconomy understands, that their additional costs could total $60 million.

And to reinforce the South Australian power grid.

As more energy sources such as wind and solar are connected to the grid, traditional power generation sources such as gas-fired units, operate less often. This has created a shortfall in system strength which was declared by the Australian Energy Market Operator (AEMO) on 13 October 2017 and a shortfall in inertia which was declared on 24 December 2018.

A secure power system needs adequate levels of system strength and inertia, which to date have been provided by traditional synchronous generators.

Following an analysis of these options, the installation of synchronous condensers on the network was determined to be the most efficient and least cost option to ensure there is adequate system strength and inertia.

On 20 August 2019, the AER approved $166 million to fund the capital cost of delivering the synchronous condenser solution.

The first two of four planned synchronous condensers will be installed at the Davenport substation in mid-2020 and the second two will be installed at the Robertstown substation by the end of 2020. They will be commissioned by early 2021.

How things change in the course of two years!

Footnote: alternate sources of voltage support

Static VAR compensators are another way of stabilising the electricity grid.

A static VAR compensator (SVC) is a set of electrical devices for providing fast-acting reactive power on high-voltage electricity transmission networks. SVCs are part of the Flexible AC transmission system device family, regulating voltage, power factor, harmonics and stabilising the system.

A static VAR compensator has no significant moving parts (other than internal switchgear). Prior to the invention of the SVC, power factor compensation was the preserve of large rotating machines such as synchronous condensers or switched capacitor banks.

Four SVC units are installed on the SP AusNet Network in Victoria – two +100 -60 MVar capacity units at Rowville Terminal Station, and one +50 -25 MVar unit at each of Kerang Terminal Station and Horsham Terminal Station.

Installed by the SECV during the mid-1980s and with a technical life of between 40 and 60 years, the control systems are now obsolete technology unsupported by the manufacturer, so an upgrade program is underway to replace them with modern equipment.

Footnote: and something really fruity

Down at Wonthaggi is a real power hog – the Victorian Desalination Plant.

It is supplied with electricity by a 88 kilometre long twin circuit 220 kV AC underground transmission line – the longest of its type in the world.

Underground 220 kV transmission line at Clyde that serves the Victorian Desalination Plant

With the underground cable run requiring something odd at the halfway point – a ‘reactive compensation station’.

Electrical transmission infrastructure at The Gurdies for the Victorian Desalination Plant

The yard full of high voltage switchgear contains three 52 MVAr oil-filled shunt reactors to compensate for the capacitance of the underground cables.

Electrical transmission infrastructure at The Gurdies for the Victorian Desalination Plant

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13 Responses to “A history of synchronous condensers in Victoria”

  1. Myrtonos says:

    The national grid is designed to operate at a consistent frequency of 50 Hertz, or 50 cycles a second.

    I actually wonder why that is, why isn’t the number of cycles per second here (or in Europe) the same as the number of seconds in a minute and minutes in an hour as is the case in most of the Americas.

    Traditional coal, gas and hydro power stations are considered “synchronous” because they use turbines or spinning wheels to produce electricity. Those spinning parts need to stay close to 50Hz to help keep the grid in synch.

    Firstly, this depends on the pole count, a 10-pole synchronous generator only needs to spin at 600 rpm to generate 50Hz. Secondly, there are asynchronous generators that need to spin a little faster than their synchronous speed, that means more than 600 rpm in case of a 10-pole induction generator.

  2. There is only brief mention in this story of batteries being able to perform the same function.
    The Tesla Very Large Battery array in South Australia has turned out to be ideal for performing this function.
    https://en.wikipedia.org/wiki/Hornsdale_Wind_Farm

    There are now plans to build one in Victoria.
    https://reneweconomy.com.au/neoen-mondo-plan-massive-600mw-victoria-big-battery-near-geelong-16169/

    • Marcus Wong says:

      I’d completely forgotten that bit – it’s been making big money in the Frequency Control Ancillary Services (FCAS) market.

      https://reneweconomy.com.au/tesla-big-battery-earns-another-4m-from-fcas-in-fourth-quarter-65127/

      • meltdblog says:

        It gets a little more complex again when the “non-syncronous” inverters only require these additional supports because they are specified to not provide any inertia (for other reasons, baked into the requirements/standards) and follow the grid variations. Its entirely possible to have wind and solar generators include virtual inertia directly into their designs from the start, but thats incompatible with the paper requirements. Its a larger transition to new ways of managing the grid, necessary to support the fluctuating renewable sources that were never considered in the original designs.

        And at that point it becomes extremely political.

  3. Tony Taylor says:

    Terrific post, Marcus. I lecture in power systems and it’s great – and not a little intriguing – to see that someone had the idea to do a history of one of the technologies we teach about.

    With baseload generation cut back, allegedly replaced by wind and solar, network stability has become a hot-button issue. Renewables running at a low output (no wind, night time) are not capable of covering for a sudden surge in consumption via, say, a large short circuit current. Musk’s Big Battery is an example of a network support device which has proved successful in stabilising SA’s network. It’s often mischaracterised as an alternate source of supply, but really it’s a network support device, just like a syncon or an SVC.

    I would love to see the numbers for the Desal link versus its competing options. Running AC underground is expensive, but if it doesn’t breakdown can be cheaper in the long run, and in long runs, which offset the initial high cost. Reactive compensation is one of those costs, and is necessary because underground cables are heavily capacitive, hence the Southern Reactive Compensation Station. But would not be the first person to wonder about the Desal’s numbers.

    Anyway, to paraphrase Prince Phillip, I didn’t come here to give a lecture. Keep up the good posts.

  4. Tony Taylor says:

    Brilliant. Thanks for that.

    I had a folder full of photos and diagrams of the Templestowe condenser, but I have a sinking feeling that I didn’t bother scanning them when I converted all my notes to digital.

  5. Tony Taylor says:

    PS: Richard Collett, I do believe we went to school together.

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