Synchronous condenser

Parallel connected synchronous condensers are mainly used for providing short-circuit power and inertia. They also help to stabilize the network through voltage recovery during faults. This becomes increasingly important with the rising share of renewable power generation that leads to a lack of short-circuit power and inertia. Due to the fact that conventional power plants are shut down, synchronous condenser solutions use a conventional generator to provide the necessary inertia and short-circuit contribution by means of its rotating mass while also providing or absorbing reactive power. 

A synchronous condenser provides short-circuit power, inertia, and reactive power for dynamic loads. Siemens Energy supplies a broad range of generators up to 1,300 MVA at full speed.

Inertia and short-circuit power are key elements of grid stability – yet their availability is shrinking. This is caused by the addition of renewables-based power generation to the energy mix, phase-out of thermal power plants, new HVDC systems, and the extension of power supply systems to remote areas. All of this influences the stability of transmission networks, resulting in a worldwide renaissance of the synchronous condenser. The Siemens Energy synchronous condenser solution comprises a horizontal synchronous generator connected to the high-voltage transmission network via a step-up transformer. It is started up and stopped with a frequency-controlled electric motor (pony motor) or a starting frequency converter. When the generator has reached operating synchronous speed, it will be synchronized with the transmission network, and the machine is operated as a motor providing reactive and short-circuit power to the transmission network.

Our synchronous condenser solutions use a generator to provide the necessary inertia with its rotating mass while also providing or absorbing reactive power. The generator is connected to the transmission network by a transformer, and is started by either an electric motor or a static frequency converter. Once operating speed is achieved, the generator is synchronized with the network and behaves like a synchronous motor with no load, providing reactive power and shortcircuit power to the transmission network.

To provide maximum inertia, Siemens Energy has extended the established synchronous condensers solution with additional rotating mass from a flywheel. This extension is a very effective method to maintain the required level of inertia and thus the RoCoF (Rate of change of frequency) of the system. Rotating mass provides an inherent synchronous inertia response (SIR), what is counteracting grid frequency fluctuations with active power injection or absorption during sudden load unbalance events.

Siemens Energy’s flywheels are operated in partial vacuum to minimize air friction losses and reduce the cooling efforts to maintain required temperature level in all operational and emergency modes. The design enables a safe emergency run-down in case of total power loss (grid black-out). The flywheel is designed for plug & play installation delivered to the site with rotor installed, lowest possible footprint and low supervision and maintenance effort.

One of our current projects - Rassau: turnkey solution synchronous condenser with Flywheel

• Short circuit power guarantees a reliable system operation and system strength
• 1100 MWs kinetic energy with the operating range of ±60 Mvar at 132 kV
• Inertia reduces oscillation on grid frequency and prevents system blackouts

Synchronous condensers help to drive the decarbonization journey for power assets. With the rising adoption of renewable energy, traditional power generation methods are utilized less, and generators are being shut down. A Brownfield rotating grid stabilizer conversion not only enables a rising share of renewable infeed on the grid but also provides a significantly reduced carbon footprint compared to a new build.