19 November 2018

Shunt reactor technology: Three world records in three years

With the increasing infeed of renewable powers, which are fluctuating by nature, achieving a reliable and secure power supply is becoming increasingly challenging. Reactors are a crucial component in meeting current and upcoming challenges. The rising need for flexibility provided by these “troubleshooters in the grid” led to three world records in reactor technology within the last three years.

Fixed vs. variable shunt reactor

Shunt reactors are used as an inductive load to control voltage and provide reactive power compensation. The target is to have a high inductive power but with small dimensions.

Shunt reactors can be designed and delivered as fixed or variable units. The fixed reactor allows only for the compensation of constant load and generation conditions and is used for HV lines and cables with stable load or generation and fixed line length.

In contrast, variable shunt reactors are equipped with on-load tap-changers (OLTC) which can change the number of connected turns and thereby change and adjust the reactance as well as handle the big load fluctuations.

With the increasing power demand and the extension of renewable power generation, there is a need for reactive power in many countries. As VSRs are cost effective, low maintenance and need less space than phase shifters or converter stations, they are an attractive solution for network operators.

2016 – First tapped variable reactor with 80% regulation range

For the first shunt reactor with 80% regulation range, load fluctuation caused by renewables was the main driver. A big TSO in Germany opted to partner up with Siemens as the most experienced shunt reactor provider to come up with a variable shunt reactor with 80% regulation range and 400 kV voltage level. Thanks to its wide regulation range, the shunt reactor does not need to be turned off and on again in order to get the right amount of reactive power to the grid. This prevents big switching impulses in the grid. The VSR also supplies enough reactive power during a black start.

The shunt reactor is built with 33 tappings to cover a rating from 50 MVAr up to 250 MVAr at a voltage level of 400kV. (Click here to get more information about this project.)

2017 – World’s most powerful variable shunt reactor ever built

The second world record – the most powerful variable shunt reactor – was built and successfully tested in 2017. Its key data are the power rating of 120-300 MVAr and a rated voltage of 220kV. It weighs 317 tons and the dimensions are approximately 10×8 5×8 meters.

Variable shunt reactors are ideally suited to support the connection of wind farms to existing power grids as they can maintain the voltage band. This enables grid operators to be more adaptable and minimize losses. This shunt reactor will balance the volatile demand of reactive power of the world’s largest offshore wind farm, Hornsea, in the UK. The relatively low sound emissions of less than 84dB (A) at 300 MVAr also add to the environmental compatibility of the units. (Click here for more information about this project.)

The energy world finds itself increasingly confronted with considerable challenges to ensure Grid stability and Efficiency. We are committed to offer our customers across the globe innovative and efficient products addressing these needs. This variable shunt reactor not only increases today’s grid security, but also enables flexibility for future changes in the German power grid”

Beatrix Natter, CEO of Siemens Transmission Products.

2018 – First ester-filled offshore shunt reactor

The rough conditions at sea as well as the volatile power production are only two of the main challenges to overcome when it comes to offshore wind parks. The cable connection of the offshore platforms requires reactive power control, which makes the use of variable shunt reactors necessary.

For environmental reasons the offshore transformers are filled with ester. Ester has high fire and flash point as well as slower aging of solid insulation. To protect the reactor from the harsh conditions at its offshore location, corrosion protection was another important measure in the manufacturing process of this unit.


With the increasing power demand and the extension of renewable power generation, there is a need for reactive power in many countries. The cost effectiveness in comparison to larger grid extension measures, as well as their robustness and low-maintenance needs, are further advantages of VSRs. The quest to integrate renewably generated power into existing grids is a challenge, but at the same time it is an exciting basis for the development of future innovative features. In collaboration with future oriented transmission and distribution grid operators, as well as wind park developers, experienced and quality-driven manufacturers can push the limits of what had seemed to be a mature technology. It is however recommended to consider not only initial cost, but also the best-in-class meantime between failures (MTBF) and references as well as the capability for consultancy on the supplier side.

Related Tags