Synchronous condensers put vital spinning inertia back into decarbonized power grids

Synchronous condensers put vital spinning inertia back into decarbonized power grids
Synchronous condensers installed at the Darlington Point Solar Farm in New South Wales, Australia (Figure 2) Source: ABB.

Strong, stable networks are essential for the reliable supply of electric power. It is increasingly challenging for network operators to maintain grid strength and stability as the generation mix shifts to renewable energy. Heikki Vepsäläinen of ABB explains how synchronous condensers (SCs) can provide vital reinforcement.

For well over a century, the world’s power grids were built on a centralized basis. Electricity took a linear path from power stations with large rotating generators, over transmission and distribution lines to consumers. This worked well, especially as utilities and network operators had a deep understanding of their systems and how to operate them to ensure continuity of supply.

In recent years, the need to decarbonize power production and integrate large levels of renewable energy has forced networks to evolve. That means the future grid looks very different (see Figure 1).

This article was originally published in Power Engineering International 4-2021.

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Large fossil fuel plants are now being replaced by renewable energy, usually wind and solar power. This has resulted in a dramatic reduction in the amount of spinning mass, otherwise known as kinetic reserve, that plays a vital role in preserving the frequency stability of the grid.

The power industry is actively seeking ways to restore this reserve. That is why attention is turning to the well-proven technology of synchronous condensers (SCs). These large rotating devices provide the physical inertia to deliver instantaneous support that maintains stability irrespective of the upstream network voltage or frequency.

How do synchronous condensers make grids more resilient?

A synchronous condenser is not a motor: it does not drive anything. It is not a generator since there is no prime mover. Instead, it’s a large rotating electric machine, deployed traditionally to produce reactive power, balancing out highly inductive loads, like electric motors.

Historically, the typical users of SCs were electrical utilities and heavy industries that operate transmission, distribution or industrial power grids. However, the changing nature of grids, and concerns over the loss of inertia, have stimulated new interest in SCs. This is because they can mimic the operation of large generating plant by providing an alternative source of spinning inertia to stabilize the grid. As large rotating machines, SCs can both supply and absorb reactive power, delivering voltage support and dynamic regulation.

A major advantage of SCs is that they are a very cost-effective and reliable way to maintain power quality. They provide the fault current protection essential for the strengthening of a weak grid. This is a key enabler for the increased grid penetration of renewables.

SC ratings

ABB supplies SCs in ratings up to 80MVAr of reactive power and 3-15kV system voltage. Higher outputs are reached by using several units in a standardized module concept. This configuration offers better redundancy and availability compared to one large unit.

SCs are tailored on the basis of network studies for the specific location where grid support is needed. This enables the creation of pre-designed SC packages that are easy to transport, install, commission and integrate. They are small or medium sized units that can be strategically sited for optimal results – providing an ideal decentralized solution to increase grid strength and stability.

SC installations

As an example of the possibilities offered by SCs, two ABB units have been installed as an integral part of the Darlington Point Solar Farm (see Figure 2). They help stabilize the local power grid as the penetration of renewable energy increases in a critical area of New South Wales. The project commenced operation in August 2020, and with a projected annual output of 685,000MWh it is the largest solar farm connected to Australia’s National Electricity Market.

Another example is that ABB is working on a project to supply an SC to SEV, the main power producer and the only distributor in the Faroe Islands, an archipelago in the North Atlantic, about halfway between Norway and Iceland.

The 53,500 people who live in the Faroes already gain around 50% of their electricity from renewable energy sources – mainly hydropower and wind. By 2030, they aim to derive all their electricity from green energy.

To maintain grid stability as wind power increases and an older thermal power plant is taken offline, SEV is installing an SC at the 6MW Porkeri Wind Farm on Suðuroy, the southernmost island of the archipelago.

The unit, manufactured at ABB’s specialized factory in Sweden, is scheduled to be up and running in the beginning of 2022. The SC, together with battery energy storage, could enable 100% of the island’s demand to be met with wind energy at times with good wind conditions.

High inertia SCs

In February 2021, ABB was awarded a contract by Statkraft, Europe’s largest renewable energy producer, to design, manufacture and install two high-inertia SCs for the Lister Drive Greener Grid Park in Liverpool, England. The innovative project will play a key role in stabilizing the local grid to handle more wind and solar power. This will help the UK’s National Grid meet its target of operating a zero-carbon electricity system by 2025.

The project will be the first ABB project anywhere in the world to feature a high-inertia configuration. This couples a 67MVAr SC with a 40-tonne flywheel that increases the instantaneously available inertia by 3.5 times.

Phoenix hybrid synchronous condenser system While SCs are a well-established concept, the technology is continuing to develop. For example, SP Energy Networks is working with the University of Strathclyde and the Technical University of Denmark to deliver the world’s first hybrid-synchronous condenser (H-SC). The H-SC’s two main physical components are a traditional SC and a power electronic static compensator (STATCOM). The STATCOM’s role is to absorb or inject fast reactive power, which helps during transient stability issues or for active filtering. The SC provides inertia, fault current support and reactive power.

The H-SC is undergoing trials at Neilston 275kV substation near Glasgow to evaluate how it can inject or absorb energy into the network to maintain the voltage within the required limits. In effect, it will provide spinning reserve over a few seconds until other resources such as a battery energy storage system (BESS) or a reserve generator can be brought online.

SCs will grow in importance

The increasing grid penetration of renewables and decommissioning of fossil fuel power plants is changing the nature of electricity networks. There is a growing need for networks to be supported by decentralized solutions that ensure grid stability and resilience. Synchronous condensers can be deployed to strengthen weak networks in remote areas. Their advantages include inertia support for frequency stability, fault level contribution and voltage regulation – all functions that are challenging to achieve only by using power electronic systems.

To illustrate the need, the two SCs in Liverpool will provide a total of more than 900MWs inertia. Currently, the UK has around 220GWs. That means Lister Drive will provide about 0.5% of the UK’s total inertia.

While that contribution seems small, as more traditional generation plants are decommissioned and renewables are added, SCs will play an increasingly important role in maintaining grid stability for the UK. This pattern is likely to be repeated globally, as SCs have already helped reinforce power networks in Australia, Canada, and Scotland. The expectation is that network operators worldwide will adopt SCs in ever-increasing numbers as the urgency to decarbonize electricity production gathers momentum.

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Heikki Vepsäläinen is President of ABB’s Large Motors and Generators Division. He holds a masters degree in electrical engineering from the University of Technology, Helsinki.

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