| Transmission & distribution


Above: Figures 2a and 2b. Synchronous condensers (left) installed at the Darlington Point solar farm (right) in New South Wales, the largest solar farm connected to Australia’s grid


Historically, this balance has been effectively self-regulated by the large spinning inertia provided by traditional rotating generators. But there is now a variety of non-synchronous resources on the grid such as wind, solar, tidal and battery energy storage (BESS). They are both intermittent and lacking any electro- mechanical connection to the grid. The result is an increased rate of change of frequency (RoCoF) that can result in systems tripping offline. The rotating mass in synchronous condensers can provide the instantaneous inertia that keeps the grid frequency within acceptable limits. They also help by damping the frequency excursions and providing more time for the operator to take suitable action to respond to frequency changes.


● Fault level contribution


When network faults occur, non-synchronous generators are unable to provide instantaneous support to avoid unnecessary tripping of loads. Their fault current capability is controlled to a level that is close to the nominal current. In contrast, the fault current response of the SC is uncontrolled and defined by its electrical parameters. This means that the fault current can be high in amplitude – possibly five times the nominal current or even higher. There is a simple reason why fault current


Generation Conv. generation


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Synchronous condenser


Synchronous condenser


Synchronous condenser


Renewable generation


Synchronous condenser


Distr. grid


Residential and small commercial


Synchronous condenser


Transportation Above: Figure 3. Synchronous condensers can be deployed in many different areas of the grid www.modernpowersystems.com | May 2021 | 13


Synchronous condenser


MV commercial


Industry/ large


Energy intensive industry


is so important. It is because the majority of the installed protection systems monitor the difference between a normal operating current and phenomena such as inrush currents and a fault current caused by a fault. This difference must be big enough to be detected easily, otherwise it is hard to protect critical assets such as transformers or switchgear.


Another important point is that measures of power quality such as voltage harmonics, unbalance and flicker relate to a defined fault level in the system. If this fault level is reduced by the introduction of significant levels of renewables then power quality issues will increase. This may result in overriding of power quality limits or could have a direct negative impact on the connected loads, such as overloading of rotating machines and transformers, or disturbing electronic devices.


● Voltage regulation


Synchronous condensers also deliver megavolt amperes reactive (MVArs) for voltage regulation. An SC cannot provide active power, it only provides reactive power. In an undervoltage condition, such as when there is a voltage dip, reactive power is produced to support the grid voltage. Equally, in an overvoltage condition, where the voltage is becoming too high, reactive power can be absorbed.


Grid Transmission grid


Where can synchronous condensers be deployed? As shown in Figure 3, synchronous condensers can be deployed in many areas of the grid to support a variety of requirements:


● Renewables


For renewable energy projects, SCs support grid code compliance. They support voltage stability and mitigate transient faults when integrating large wind farms. SCs can also combat phase- locked loop (PLL) synchronisation instability in converters, as well as limitations in the power infeed caused by low short circuit level (SCL). Solar farms can use SCs to increase revenue by boosting active power output as otherwise part of the total inverter power has to be assigned for reactive power compensation.


● Conventional power generation In conventional power generation synchronous condensers mitigate frequency instability that occurs through the imbalance of peak demand and renewable power – they help prevent an increased RoCoF.


They also support the grid with inertia and offload reactive power from generators during peak or ramp times (“duck curve”). SCs can enable power generation operators to sell additional ancillary services such as higher


Industrial and large commercial


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