Above: ABB synchronous condenser
Traditionally, the world’s power grids have relied on the spinning inertia, or kinetic reserve, inherent in large, centralised generation plant to keep them in balance. This inertia helps grids to resist sudden changes, such as when a generator trips offline. The result is that the system frequency can be maintained within tightly controlled limits.
The grid inertia originates from hundreds of generators operating in synchronisation. In effect they are “locked” together so that they all rotate at the same speed, and therefore the same frequency. The cumulative energy stored by all these synchronous generators provides a fast response, available within seconds, to any interruption in generation. That is sufficient time for the grid control system to detect the issue and take appropriate action to ensure continuous operation.
While the increasing grid penetration of wind and solar power is essential for the transition to a decarbonised energy system, it presents a new challenge for grid operators. The reason is that renewable resources are not synchronous and therefore cannot contribute inertia to the grid. At the same time, large synchronous power plants are being taking out of service. Hence, there is a significant net loss of inertia.
Growing concerns over inertia have prompted renewed interest in synchronous condensers (SCs).
These large rotating devices can mimic the operation of large generating plant to put the missing inertia back into the grid. They are proving to be a very cost-effective and reliable way to maintain power quality as well as providing the fault current protection essential to strengthen a weak grid.
In terms of design, synchronous condensers look very similar to large motors and generators. However, the synchronous condenser does not drive anything so is not a motor. It is also not a generator as it doesn’t have a prime mover. Fifty or more years ago, SCs were integral to almost every grid, where their role was to produce reactive power to balance out highly inductive loads on the grid, like electric motors. That role was supplanted by modern power electronics.
High-inertia SCs for Statkraft in Liverpool
Statkraft, Europe’s largest renewable power producer, has ordered two high-inertia SC systems for the Lister Drive Greener Grid project in Liverpool, England. This innovative project will play a key role in stabilising the local grid to handle more wind and solar power, helping National Grid meet its target of operating a zero-carbon electricity system by 2025.
The project is the first anywhere in the world to feature ABB’s high-inertia SC configuration. It couples a 67 MVAr SC with a 40 tonne flywheel, multiplying the instantaneously available inertia by 3.5 times. The main advantage of this approach, which combines a mid-size SC with a flywheel, is that the system losses are much lower compared to providing the whole inertia required from a synchronous condenser installation. Coupling two mid-size SCs together also offers a high level of redundancy, increased inertia and greater controllability.
Statkraft’s units at Lister Drive will together provide a total of more than 900 MW.s (megawatt-seconds) of inertia. That means the site will contribute about 1% of the UK’s projected minimum total inertia requirement for 2025.
Construction is well advanced. The SCs have been delivered and are being commissioned, with the facility expected to be online in early 2023.
To ensure round-the-clock availability for this vital system, Statkraft has signed a 10-year services contract with ABB’s UK field service team to provide a full range of maintenance services, both planned and quick response. Digital condition monitoring solutions will be deployed to optimise performance and predict maintenance needs. By assessing real-time data with cloud-based analysis, the team will be able to plan corrective actions before issues occur, ensuring system reliability.
SCs will help the Faroe Islands transition to 100% renewables
The Faroe Islands in the North Atlantic have the ambition to become the world’s greenest group of islands by meeting all their energy needs from renewable resources by 2030. To achieve this, SEV, the power utility intends to use green electricity from hydropower, solar, wind, and, potentially, tidal streams. The transition will offer important economic benefits as the Faroe Islands will no longer be dependent on expensive fossil-fuel imports.
The challenge for SEV is that switching off the current diesel-fueled generating plant could impact the stability of the grid. This could affect the fish processing and aquaculture industries that are a major contributor to the Faroese GDP. To add to the challenge, the Faroe Islands cannot call on external grid support as there are no power cables connecting the islands to neighbouring countries.
To keep the grid in balance, SEV is working with ABB to install synchronous condensers. The site for the first installation is the 6 MW Porkeri wind farm on Suðuroy. This electrically isolated island is the southernmost in the archipelago. The unit is now ready for operation. Together with battery energy storage, the SC could enable wind energy to meet 100% of the island’s demand at times with good wind conditions.
SEV’s next installation will be a similar unit at Sund, close to Tórshavn, the Faroese capital, on the island of Streymoy. This is scheduled to be online in 2023.
A growing need for synchronous condensers
Existing SC installations are already playing a vital role in reinforcing networks in Australia, Canada and Scotland in diverse applications from solar power farms to remote mining operations. The worldwide drive for decarbonisation will see traditional power plants decommissioned in ever greater numbers. That means the inertia gap will continue to grow, so synchronous condensers are set to become an increasingly important technology for maintaining grid stability.
Author: Kristina Carlquist, general manager, synchronous condensers, ABB
For more information please visit: https://new.abb.com/motors-generators/synchronous-condensers
