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Shunt reactors and series reactors are used widely in AC networks to limit overvoltage or shortcut current in power transmission. With a growing number of high-voltage overhead lines in a fast-changing energy environment, both shunt and series reactors play a key role in stabilizing network systems and in increasing grid efficiency.
Reactors are real all-rounders and grid trouble-shooters. In conventional electricity transmission grids shunt reactors control voltage and compensate reactive power, while series reactors change load flow and limit short-circuit currents. With the increase of renewable and distributed power generation reactors – and variable shunt reactors in particular – play a significant role in today’s energy landscape with its higher fluctuation in power feed-in. Siemens' reactors come with benefits at various levels to help grid operators achieve and maintain a reliable and secure power supply system:
The high number of units in service – more than 800 units manufactured over the last decade alone – serves as proof of the validity of our design laws. In our effort to ensure long and reliable service life, we strive for minimum tolerances in manufacturing and insist on high-quality materials. Our suppliers worldwide are required to comply with the high standards, to which we hold ourselves. The result is a failure rate that is nothing short of impressive – we’ll gladly provide you with our latest mean time between failures (MTBF) figures.
MTBF1) of Siemens shunt reactors
Number of units: 820
Total service years: 4,361
Number of failures: 5
External failure rate: 0.115 %
Meantime between failure: 872 years
1) 2004-2013 evaluated
Case study: How to measure transformer reliability
Our systematic approach to quality supports our relentless pursuit of precision and customer satisfaction. It rests on three pillars:
We build on decades of experience to achieve the high signature precision of our reactors. Low levels of vibration, noise, and losses, which remain stable over the entire service life, require utmost precision at every stage of the manufacturing process, from manufacturing to testing. To ensure this precision we employ highly qualified personnel and our very own design analysis tools.
Siemens shunt and series reactors are the most cost-efficient solutions for reactive power compensation and short-circuit current limitation in the market. They come with strong commercial customer benefits, such as lower reactive power demand, lower losses and higher grid capacity. Their balanced load flows enable customers to avoid expensive grid extension.
The design process for reactors differs radically from that of transformers: Owing to their special core, the mechanical design of reactors tends to be more complex and demands particular attention to physical characteristics. In their communication with customers, Siemens experts share comprehensive advice on desired and necessary design features and will support customers with recommendations.
Reactor design criteria
In addition to developing its own reactor design software, Siemens R&D collaborates with major universities and partners worldwide to improve the quality of its products and services. Siemens' skilled experts use state-of-the-art design software and simulation tools, such as Siemens software based on the Finite Elements Method, i.e. 3DFEM for core and yoke losses of shunt reactors, and 3rd-party tools, such as ANSYS© and Open Foam®.
The low levels of vibration, noise, and loss, which have become Siemens' trademark in the industry, require utmost precision at every stage of the manufacturing process and exacting standards in supplier management. To prevent torsion flexion, Siemens Nuremberg uses core stacking tables designed for cores of 300 hundred tons, which shift core from their horizontal layer position into the vertical assembly position. Our oil-filled reactors are manufactured in two design types − with air core or with iron core.
Held in place in a clamping frame, the iron core in a reactor is clamped together by tie rods made of steel and/or limbs. Siemens’ unique spring technology between the tie rod and crossbeam ensures constant core pressing. This way, Siemens' spring and clamping design constantly maintains lowest noise and vibration values over the entire service life of these units. Siemens offers two types of clamping:
Siemens manufactures the full range of reactors for all customers’ needs in a variety of application areas. Series reactors are deployed for short-circuit current limitation and load flow changes. Shunt reactors provide voltage control and reactive power compensation. They can be designed as variable shunt reactors with tap changers for customers requiring a more flexible solution.
Shunt reactors (SHR) are arranged between line voltage and ground. Their place of installation is usually located at the start or end of a long overhead power line or cable connection, or in central substations. While overhead power lines are of comparably low capacitance and therefore only require compensation at high voltages and/or along very long power lines, cables have a significantly higher conductor-to-ground capacitance (by a factor of 20). Therefore, compensation should be provided already for lower voltages and shorter cable lengths.
Typical application areas
Reactive power compensation and voltage control
Fixed shunt reactors are designed for defined system condition and used for voltage control & reactive power compensation. They are budget and easy ON/OFF device. However, when multiple units are placed in parallel, fixed shunt reactors can be more expensive than variable shunt reactors. Their compact design and low maintenance needs make them a perfect solution for increasing efficiency.
Typical application areas
A profitable investment thanks to full flexibility
Variable shunt reactors are used for voltage control and reactive power compensation. They continuously adjust reactor power rating to actual needs. Use of variable reactors is particularly recommended if fluctuations occur. This is the case for a growing number of grids, due to the increased use of renewable energy sources. Depending on actual demand, the reactive power can be adjusted to the actual grid.
Variable shunt reactors by Siemens are not only designed as compact units for on-going adjustment to changes in grid conditions, but are also low-maintenance units with minimal service demands. Siemens uses the reliable VACUTAP VRG tap changer series by Maschinenfabrik Reinhausen.
These on-load tap changers execute up to 300,000 switching operations maintenance-free. With a large control range of max. 20 to 100%, variable reactors offer a grid flexibility that enables operators to achieve the highest grid efficiency. Other interesting advantages of this flexibility: Switching in a variable shunt reactor with a low reactive power rating results in a smaller switching impulse. Also, operator profit from lower losses and noise emissions when the variable shunt reactor operates at a low power rating.
Typical application areas
Siemens Transformers manufactures series reactors up to 800 kV and 1,500 MVAr, usually as oil-filled units with an air core. Depending on customer needs, however, they can also be designed with an iron core, especially for neutral-point grounding reactors.
Typical application areas
Series reactors are used to control current and increase impedance. As their name suggests, these reactors are arranged in series with the existing line. The series reactor constitutes an impedance in the grid and thereby increases the resistance of the network segment to limit short circuit currents or shift load flows. Arc-furnace series reactors, for example, provide additional reactance to stabilize the arc and increase efficiency. In motor start-up reactors, the starting current is limited and - where appropriate - combined with a speed controller.
For over 100 years, we have closely cooperated with energy providers and grid operators. Drawing on these decades of experience, we have tailored our processes − from consulting to design, from manufacturing to testing and after-sales services − to meet the needs of our customers and their highly customized units.
Shunt reactors provide voltage control and reactive power compensation, but can also be designed as variable shunt reactors with tap changers. VSR are used to compensate for capacitive reactive power of transmission lines – particularly in grids operating at low-load or no-load condition. They reduce network-frequency overvoltage in case of load variation, shedding, or network operating at no load. Moreover, VSR improve the stability and economic efficiency of power transmission.
The decision to opt for a fixed SHR often has technical reasons, but the - admittedly more substantial - investment in a variable shunt reactor does pay off: With increasing load fixed shunt reactors will overcompensate the voltage increase, resulting in an overall voltage drops, while variable shunt reactors always compensate accurately and adjust to the current load situation.
If your answer to one or more of the following questions is “yes”, you should consider opting for a VSR:
In 2008, Siemens emerged as the world’s first supplier of 800-kV HVDC transformers and, since then, has completed several 800kV HVDC projects every year. We followed up with the successful tests of the world’s first 1100kV HVDC mock-up, and, in 2013, of the world’s first 400kV transformer with alternative liquids. Our customers benefit from our dedication to their future success.
5 VSR, 400 kV/50-250 MVAr, 425kW (at 250 MVAr/400kV)
Meets high demand for compensation arising from renewable energy sources
Offers high regulation range improving black-start capability after blackouts
40 single-phase shunt reactors, 765/√3 kV, 100 MVAr, low-noise 75 dB
At 146 kW, particularly low-loss performance
High reliability at high voltage level
Get insider insights
In an interactive PDF, Siemens reactor experts share their insights into standard specifications for variable shunt reactor, list recommended values and highlight cost drivers in reactor design.