Cooled condenser SC

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Overview
Parallel-connected synchronous condensers are used to provide short-circuit power, system inertia and reactive power support for transmission networks. They stabilize voltage during faults and help maintain frequency by contributing rotating mass. Synchronous condenser solutions employ a conventional generator operating without prime load to deliver these grid-stabilizing services. Siemens Energy supplies a broad range of generators suitable for synchronous condenser applications, with ratings up to 1,300 MVA at full speed.

Key benefits

• Provides short-circuit power to the transmission network
• Supplies inertia (rotating mass) to stabilize frequency and reduce RoCoF
• Delivers or absorbs reactive power for voltage support
• Enables short-term overload capability during emergencies

Proven solution for grid stabilization
A synchronous condenser supplies short-circuit power, inertia and reactive power for dynamic loads. Siemens Energy offers generators and complete packages engineered for grid-stabilization duties, covering a wide range of ratings and site requirements.

Working principles
Units are connected to the transmission system via a step-up transformer. The generator is started by a pony motor or a starting frequency converter. When synchronized at synchronous speed and run unloaded, the machine operates as a synchronous motor providing reactive power and short-circuit contribution to the grid.

Main components and functions

• Generator step-up transformer — customized transformer between generator and grid
• Isolated phase bus — isolated high-energy bus between generator and step-up transformer
• Generator circuit breaker — connects/disconnects the synchronous condenser; unit protection
• Auxiliary transformer — supplies auxiliary systems
• External coolers — generator cooling system
• Static / brushless excitation — regulates generator voltage and reactive power
• Synchronous generator — increases short-circuit power, stabilizes frequency via inertia, controls reactive power
• Optional flywheel — adds rotating mass to enlarge inertia

Maximum inertia with flywheel extension
To maximize inertia, a flywheel can be added to increase rotating mass. Flywheels enable a synchronous inertia response (SIR) that injects or absorbs active power during sudden imbalances. Siemens Energy flywheels are designed for plug-and-play installation, operate in partial vacuum to reduce air friction, support safe emergency run-down in case of total power loss, and are delivered with the rotor pre-installed to minimize footprint and maintenance.

Application example (project highlights)

• Rassau: turnkey synchronous condenser with flywheel
• 1,100 MWs kinetic energy with an operating range of ±60 Mvar at 132 kV
• Inertia reduces frequency oscillations and helps prevent system blackouts

Synchronous condenser in the energy transition
With growing renewable generation and the phase-out of thermal plants, available inertia and short-circuit power are decreasing. Synchronous condensers, including brownfield conversions of rotating machines, enable higher renewable penetration with a lower carbon footprint than keeping conventional plants online solely for stability.

Additional notes
The solution supports voltage recovery during faults, provides controlled reactive power for dynamic loads, and can offer increased short-term ratings during contingencies depending on machine specifications.

Technical specifications

• Generator ratings available up to 1,300 MVA (at full speed)
• Provides short-circuit power, reactive power control and inertia (rotating mass)
• Starting methods: pony motor or starting frequency converter
• Connection to grid: via step-up transformer
• Flywheel option: increases inertia; flywheels operate in partial vacuum; designs enable safe emergency run-down
• Typical project example: 1,100 MWs kinetic energy (Rassau) with ±60 Mvar operating range at 132 kV
• Maximum single-flywheel kinetic energy examples: up to ~3500 MWs (50 Hz) and ~2000 MWs (60 Hz) depending on material and design
• Short-term overload capability: dependent on machine specifications
• Key auxiliary components: auxiliary transformer, isolated phase bus, generator circuit breaker, external coolers, static/brushless excitation