Phase-shifting transformers


Creating balance within and between networks

In power grids, phase-shifting transformers provide active power flow control. By enforcing or blocking loads, they not only improve the stability and flexibility of grids but also help grid operators get the most out of existing hardware.   Ratings: ≤ 1.200 MVA ≤ 765 kV Features: Compact design; low noise; high phase-shift capability Options: Ester insulation; low noise, etc.    

Explore how to best approach the specifications for your phase-shifting transformer.

Download info package


An efficient and cost-effective way to control power flow

In an increasingly complex power-generation landscape and a growing energy market, the capability to control the flow of power is fast gaining in crucial importance. This is the area, where phase-shifting transformers (PST) excel. They protect lines, make grids more reliable, and reduce transmission losses. And they are among the most economic and cost-efficient solutions for power-flow management out there.

Avoid expensive grid extensions

In a grid struggling with unwanted power flows from adjacent networks – for example, due to the hard-to-control feed-in from renewable power plants – phase shifters protect from additional loads. By changing the effective phase displacement between the input voltage and the output voltage of a transmission line as needed, phase shifters enforce, block and even revert power flow as well as reduce or eliminate loop flows. Phase shifters can rebalance line loading between parallel lines or network sections.


Grid operators use this capability to increase the transmission capacity of the network, while minimizing expensive grid expansions. A decisive step toward ensuring the stability and reliability of your own grid and enabling strategic energy planning.

Operators can use phase-shifters to…

  • balance in the increasing amounts of renewable power.
  • stabilize power flow over long transmission distances between power generation centers and load centers.
  • control high-volume electricity trading between countries or different system operators.
  • reliably satisfy local peaks in electricity demand in urbanized areas.
  • provide electricity-intensive plants with energy directly from neighboring small power plants, e.g. CHP .    

Areas of Application

The fast-transforming energy landscape of heterogeneous power grids presents operators with similarly fast emerging challenges. Their capability to ensure grid stability and reliability – and actively balance in shifting amounts of power from renewable energies – make these transformers a versatile must-have for competitive grids.

We give you flexibility, reliability, and efficiency

Siemens' sustained experience in phase-shifter design and rigid dedication to quality not only ensure smooth and on-time project execution. More importantly, they ensure that customers enjoy the full benefits of reliable performance over the long service life of their custom-designed unit. However, there are more advantage to relying on Siemens for a phase-shifting transformer:    

Get the most out of your phase-shifter

As the most cost-efficient solution for power flow control, phase-shifting transformers contribute to the financial success of grid operators in a competitive energy environment. With their trademark reliability and efficiency, Siemens' tailored-to-fit phase shifters come with a wide range of competitive advantages. But what really makes Siemens transformers stand out is the extensive in-depth design and spec support.


Creating a perfect fit for your grid

Once specifications have been set, a tender can only achieve so much in ensuring a cost-efficient result. Therefore, Siemens offers customers a collaborative and iterative approach to defining specifications. The experts of Siemens Power Technologies International (PTI) share their insights into which combinations of specifications drive cost and performance, while the customer’s network planners have a clear picture of the required capabilities their new transformer.


This Siemens approach combines their expertise to give customers a perfectly tailored transformer – the most cost-efficient and robust solution to the performance they need.


How Siemens‘ phase-shifting transformers benefit operators

At the company level, by

  • Increasing grid stability
  • Creating greater flexibility in accommodating network changes
  • Offering greater independence from other grid operators

In their business performance, by

  • Increasing active power capacity of grid
  • Allowing for direct power sourcing
  • Enabling commercial trading
  • Providing a cost-efficient solution for power flow control
  • Optimizing losses*
  • Giving operators greater leeway in planning major grid extension investments

During operation, by

  • Controlling flow control and regulating voltage
  • Stabilizing the grid
  • Reducing or increasing active power loading of specific lines
  • Preventing line overloads
  • Blocking – or even reversing – power
  • Reducing and/or eliminating loop flows

* Depends on ratio of impedances-line resistances

A holistic approach: from customer challenge to energization on site

With Power Technologies International (PTI), Siemens has established a service that goes beyond finetuning customer requirements. Its subject-matter specialists run grid studies that go toward building a comprehensive profile to answer the key question: What capabilities does the phase shifter need to solve the customer’s pain points?


Transcending the specs

This holistic approach ensures that a customer’s specific needs and situation inform all decisions, from the very first project stage to the energization on site. PTI’s unique perspective produces phase shifters, which not only are built to specs, but come with greater flexibility in addressing the customer’s challenges. 

Customers benefit from…

  • Siemens in-depth know how in designing phase-shifting transformers
  • more than 50 years of experience in phase-shifter design
  • specialist designers and phase-shifter design tools
  • design rules and tools with a track record of excellent test results and highest ratings
  • a multitude of options, from dual-tank solutions with “faltenbalg” to oil-oil bushings

Ensuring quality in the supply-chain

Siemens Transformers rigorously vets its suppliers. Selected partners comply with the Siemens supply-chain standards, emphasizing total cost, commitment to quality, and environmental awareness.    


Siemens' dedication to quality ensures...

  • a precise manufacturing process with very low manufacturing tolerances
  • exacting standards for sub-supplier qualification
  • an outstandingly low failure rate1
  • a stable product performance over the entire lifetime

1Failure rate only available for AC transformers in total   


Our power system consulting services range from power system studies and field measurements to disturbance investigations.


Talk to our PTI experts

From assembly, straight into the test field

Siemens transformers are well-known for their superior first-pass yield. They undergo rigorous testing at Siemens own test facilities before they are shipped to the customer. This approach – along with Siemens signature precision in manufacturing – ensures compliance with guarantee values and a successful operation in the field.


Enough space to test fully-assembled units

Siemens test bays are uncommonly spacious. Why? To ensure reliable performance in their target environment, Siemens engineers rigorously test fully-assembled units in their test bays – even towering giants, such as dual-tank phase shifters.

Highlights in phase-shifter innovation

Since its very beginning, Siemens has worked closely with customers to push the limits of transformer technologies. Their shared goal? To maximize the product value for each specific use case. Milestones range from redefining limits, such as voltage level or maximum phase shift, to finding Siemens answers to global challenges our customers face – answers, which include compact low-noise units for urban areas as well as the first phase shifter with an environmentally-friendly ester insulation.    

Types of phase-shifting transformers

Phase-shifting transformers are highly complex units. To meet the unique needs of each customer, Siemens phase shifters are custom-designed and manufactured to specification.

You have questions? We have answers

We organize webinars and other events to give grid operators an opportunity to ask specific questions about phase-shifters. Here are examples from our latest Q&A session.

Standard substation transformer tap changers are used in phase shifters, as well. However, the designer has to consider the overexcitation in retard operation, that is to say, the increased voltage across RW. According to the established standard, a tap changer must be able to switch 2x the rated current. Overexcitation often necessitates limiting the overload. You can use a standard TAPCON controller.

Currently, there is no thyristor tap changer for large power transformers. The standard for a switch is appr. 5.4 sec/tapWith fast-switiching gear the value drops to 2.7sec/tap.

You will need studies on Load Flow, Short Circuit, Dynamic, and Switching Transient & Protection. You may also require more specialized studies for any number of reasons, such as the particular region, in which you are located. For example, if the lines in the region are not transposed, you will need to conduct an Unbalanced Load Flow Study. Other studies may focus on the impact on harmonic power flow or subsynchronous oscillations.

400kV, yes, but we have not yet seen a 765/765kV PST. However, there are 765/400kV auto transformers with a perpendicular voltage component to the common neutral.

Learn more about phase-shifter specifications

View our 2017 webinar

Downloads and Support

Make use of our services

For your convenience, we have gathered relevant downloads in one spot. If your question is still unanswered, please feel free to contact our Energy Support Team.

Contact the Energy Support Center

Energy Customer Support

+49 180 524 70 00

+49 180 524 24 71

Energy Customer Support

Freyeslebenstrasse 1
91058 Erlangen


Making a difference

Siemens phase shifters are built for operations and environments all over the world. They not only meet highest customer requirements, but comply with both national and international standards.    

Protecting the Polish grid from North-South power flows in Germany




/410 kV ±20°



These 4 phase shifters protect the grid of Polskie Sieci Elektroenergetyczne S.A. in Poland from the north-south power flows caused by green-energy generation in Germany.

For more energy trading and export

50 %

ONAN low-loss rating


/400 kV ±40°


x 600 MVA

These two units with a high phase shift ensure fast reconnects in the Slovenia-Italy grid. They facilitate Elektro· Slovenija, d.o.o.’s trading and exporting of power.    

Big angles, unprecedented leeway




/230 kV -80º/ +31º


x 400 MVA

With a phase angle of -80º/ +31º, these phase-shifters come with the highest regulation range ever. San Diego Gas & Electric (SDG&E) uses them to reduce power flow to its substations and to push more power on the transmission lines to its main load center.

Info package

Download free info package

Explore how to best approach the specifications for your phase-shifting transformer.    


Get in contact with our Sales Support and Customer Service for Power Transmission and Distribution

Do you need help on a concrete project? Do you need a quote for any of our products or solutions? Do you need support for your installed equipment? Do you have a technical question? Do you need something totally different? You can contact us 24/7. We are looking forward to your call or online request.   Phone +49 180 524 70 00