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. Phase-shifters are available in a range from ≤ 2000 MVA and ≤ 765 kV. The design is compact with low noise, high phase-shift capability and also available with Ester insulation.

Next level of eco-friendliness - worlds first phase-shifter with ester insulation

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Our phase-shifters are an efficient and reliable 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 crucial. Phase-shifting transformers of Siemens Energy protect lines, make grids more reliable, and reduce transmission losses. Increase the transmission capacity of your network and ensure grid stability, while minimizing expensive grid expansions with custom-designed Siemens Energy phase-shifters! They are among the most economic and cost-efficient solutions for power-flow management out there.

A holistic approach: from customer challenge to energization on site

Siemens Energy has established a service that goes beyond finetuning customer requirements. 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?

Once specifications have been set, a tender can only achieve so much in ensuring a cost-efficient result. Therefore, Siemens Energy offers customers a collaborative and iterative approach to defining specifications. The experts 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 of their new transformer.

This Siemens Energy approach combines expertises to give customers a perfectly tailored transformer – the most cost-efficient and robust solution to the performance needed.

This holistic approach ensures that customer specific needs and situations affect all decisions, from the very first project stage to the energization on site. Our 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…

  • 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

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 Energy's tailored-to-fit phase-shifters come with a wide range of competitive advantages.

  • Increasing grid stability
  • Greater flexibility in accommodating network changes
  • Greater independence from other grid operators

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

  • 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

* Depends on ratio of impedances-line resistances

Ensuring quality standards

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

Assembled phase-shifting transformers undergo rigorous testing at Siemens Energy's own test facilities before they are shipped to the customer. These approaches – along with Siemens signature precision in manufacturing – ensures compliance with guarantee values and a successful operation in the field.

  • Exact standards for sub-supplier qualification
  • Precise manufacturing processes with very low manufacturing tolerances
  • Outstandingly low failure rate*
  • Stable product performance over the entire lifetime

*Failure rate only available for AC transformers in total

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

Siemens Energy's test facilities accommodate test objects of up to 35 Meters (m) in length, 18 m in width and up to 21 m in height. To give you an idea of the dimensions: This Con Edison  575 MVA - 345 kV PST comes with 19.8 m x 13.1 m x 8.9 m.

Rendering of a phase-shifting transformer

With phase-shifting transformers customers avoid expensive grid extensions

The fast-transforming energy landscape of heterogeneous power grids presents operators with similarly fast emerging challenges. 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 and ensure grid stability and reliability by actively balancing shifting amounts of power. 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 flows as well as reduce or eliminate loop flows. Phase shifters can rebalance line loading between parallel lines or network sections.

Types of phase-shifting transformers

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

Quadrature booster

  • MVA rating dependend on phase angle
  • All voltage levels
  • Safe solution (regulating winding in neutral end)
  • One 3-phase-OLTC for low powerratings
  • Largest phase angle and ratings possible
  • Expensive
  • Available in two tank and single tank design

AUT or double wound transformer with auxiliary transformer

  • MVA rating dependend on phase angle
  • All voltage levels
  • 20° phase angle
  • Non-symmetrical
  • High power ratings possible
  • Used as NET transformer with additional phase angle regulation
  • Expensive but cheaper than quadrature booster
  • Available in two tank and single tank design

Double wound transformer

  • 300 MVA
  • 40 kV
  • 20° phase angle
  • In line regulation and pahse angle regulation
  • OLTC in star connection
  • High number of winding leads
  • Most expensive aingle sore solution, but cheaper

Hexagonal solution

  • MVA rating dependend on phase angle
  • 230 kV
  • Very cheap
  • Single regulation winding
  • Symmetrical
  • OLTCs exposed to system disturbances
  • Different retard/advanced phase angle

Extended delta solution (symmetrical)

  • MVA rating dependend on phase angle
  • 230 kV
  • Cheap
  • Symmetrical
  • OLTCs exposed to system disturbances
  • Two regulating windings

Extended delta solution (unsymmetrical)

  • MVA rating dependend on phase angle
  • 230 kV
  • 15° phase angle
  • Very cheap
  • Single regulation winding
  • OLTCs exposed to system disturbances
  • Unsymmetrical

Making a difference

Siemens Energy 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.

Make use of our services

For your convenience, we have gathered relevant downloads in one spot.

Use Case Providing grid stability
PDF (254 KB)
Use Case Next level of eco-friendliness
PDF (305 KB)

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You have questions? We got the answer!

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.