Grid Quality

Applications of synchronous condensers

The increasing penetration of renewables, particularly wind and solar, in the energy mix, and the decommissioning of fossil fuel power plants are together bringing about changes in the structure of electricity networks. With greater capacities of solar and wind power being integrated into the grid, its balancing has become an issue. Further, electric vehicles and rooftop solar are becoming more common and require advanced power demand and supply management at a local level. Thus, future networks with decentralised power generation will require specific distributed solutions to ensure grid stability and resilience.

To this end, conventional power plants’ large, high inertia synchronous generators, which supplied the grid with short- circuit power and rotating mass, are being taken out of service. In this evolving power sector landscape, synchronous condensers can instead provide additional short-circuit power to strengthen the grid, help to maintain grid quality, and provide fault ride-through capability. Synchronous condensers are rotating electrical machines that resemble synchronous generators. However, they are not technically generators as they are not driven by an engine or turbine. Neither do they come under the category of synchronous motors, as they do not drive any load. Instead, they are large rotating machines that adjust fluctuating conditions of an electric grid. Installed at strategic intervals along a power transmission system, synchronous condensers help maintain power quality. These synchronous condensers are applied across the industry, from renewable and fossil fuel power plants, through transmission and distribution systems to industrial electricity consumers.

Synchronous condensers can be deployed to strengthen weak networks in remote areas to cater to various applications like provision for reactive power and synchronising torque, generation of short-circuit current and damping of low-order system harmonics, as well as provision of instantaneous inertia up to 460 MW per system. For catering to power demand for a higher inertia, multiple systems can be combined to allow redundancy.

A synchronous condenser is also well suited to operate during overload for shorter or longer periods of time and can support the power system voltage during prolonged voltage sags by increasing the network inertia. It can therefore be utilised as Volt- Amp Reactive (VAR) compensating a device in situations where voltage instability must be prevented at all costs.

  • There are many advantages of installing synchronous condensers in weak network areas:
    Provide reactive power and synchronising torque
  • Provide effective support for grid restoration
  • Provide significant short-circuit current
  • Contribute to small signal and transient stability and act as a “sink” to correct low-order system harmonics and phase unbalance
  • Provide instantaneous inertia (synchronous inertia) up to 100-460 MW per system lProvide voltage support and dynamic regulation by generating/absorbing reactive power
  • Can conveniently be integrated with fast dynamic mega volt-ampere reactive (MVAr) providers like statcoms, static VAR compensators, HVDC links, wind or solar inverters, as well as storage converters.

Even existing out-phased generator set- ups can be modified and used as synchronous condensers. However, these generators are often old machines that require costly, substantial complex modifications of the machine itself including lubrication and cooling systems, excitation and controls, and starting methods. The total efficiency often does not meet modern machines and they cannot be optimised for today’s requirements. Hence, specifically designed, modern and efficient synchronous condensers should be deployed. Further, they should be optimised for the performance required at the specific decentralised location with well-known technology for adequate grid upgrades. With the increasing requirement for grid stabilising solutions, many companies are providing such products that are designed for ensuring power quality. For instance, ABB supplies synchronous condensers that are compact units of up to 70 MVAr and can be deployed exactly where grid support is needed. They are designed on the basis of network studies and therefore tailored to provide maximised grid support. Compared to larger units derived from turbine generators, they provide better angular stability and higher overloadability.

Conclusion

With sustained growth in the use of renewables, synchronous condensers are gaining wide acceptance from electricity utilities and grid operators. As a well-established and proven technology, they can play an important role in strengthening the quality and resilience of today’s electricity grids.

 

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