A stable grid in the era of renewables

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.

Synchronous condenser at a glance

Proven solution to stabilize the grid

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.

Synchronous Condenser

Technology and system overview

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.

External coolers

Cooling system for the generator

Auxiliary transformer                   

Power supply for auxiliary systems

Generator circuit breaker

• Connects and disconnects synchronous condenser to and off the grid

  • Protects the synchronous condenser 

Isolate phase bus

Isolated high-energy bus between generator and step-up transformer

Synchronous generator

• Increases short-circuit power level

• Stabilizes frequency with its inertia

• Controls reactive power

Generator step-up transformer

Customized transformer between the synchronous generator and the grid

Static/brushless excitation

Adjusts generator voltage

and reactive power

Maximum inertia with additional masses provided by flywheel solution

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.


Additional information


Our solutions in practice

Many of our products and solutions are already being successfully used. Below is an example of these applications.
News and events

What’s new with synchronous condenser

The latest information on Siemens Energy's synchronous condenser

Be in control

Paving the way for renewables

With the rise of renewable power generation and the retirement and shutdown of thermal power plants, synchronous condensers have to take over the part of providing enough inertia and short-circuit power. At Siemens Enegry, we provide tailor-made turnkey synchronous condenser solutions up to 1,300 MVA to address our customers’ needs based on proven, reliable in-house equipment, extensive know-how of transmission system requirements, and project execution experience.