How to increase transmission system capacity and stability

Fixed series capacitor (FSC)

The ongoing transformation of the energy system requires effective means to cope with growing challenges when it comes to reliable power transmission. Instead of building new lines to provide sufficient transmission capacity, it’s often better to use our flexible AC transmission systems (FACTS) technology to increase the transmission capacity. Both newly built transmission lines and existing systems benefit from Siemens Energy’ fixed series capacitor (FSC) which is part of the series compensation (SC) solutions that also help to improve the quality and stability of power transmission lines.

Fixed series capacitor at a glance

Boost your transmission lines

Innovative series compensation technology provides higher transmission capacities for existing long-distance AC transmission lines and increased grid stability without the costs and time-requirement of building new lines.

For decades, fixed series capacitor (FSC) technology from Siemens Energy has improved grid stability and contributed to the optimal utilization of transmission lines. Transmission system operators around the world have already benefited from solutions that were tailored to their specific requirements. Among the main benefits of fixed series capacitor are the reduction of line voltage drops, limitation of load-dependent drops, and a reduction of the transmission angle.

Proven fixed series capacitor technology for cost-effective capacity expansion

The amount of power that can be transferred with long overhead transmission lines is limited by the impedance that can lead to voltage drops. For decades, fixed series compensation is the proven solution to maintain a minimum voltage profile and maximize utilization of transmission lines. 

It works by connecting a capacitor bank in series with the transmission line to partially compensate the inductive impedance of the line while also increasing the voltage at the point of connection. The capacitors are protected by metal-oxide varistors (MOV) and – in case of a fault – by tripping the FSC and closing the bypass breaker. For instant protection, a triggered spark gap bypasses capacitors and MOVs within less than 1 ms. Even gap-less solutions are possible, provided that local requirements match. Due to this complexity Siemens Energy recommends and offers individually designed solutions with fixed series capacitors.