The Giant of Amprion

German grid oper­ator Amprion wanted the largest and most powerful phase shifter in the world. For this to work at all, there first needed to be a revo­lu­tion in on-load tap-changers.

Humanity wants to move more and more energy simul­ta­ne­ously, which requires large high-perfor­mance trans­formers of all types: those for HVDC trans­mis­sion across entire coun­tries, those for many indus­trial appli­ca­tions, such as elec­tric arc furnaces for steel­making, or vari­able shunt reac­tors for reac­tive power compen­sa­tion. For Amprion, this means powerful phase-shifter trans­formers or, more precisely, the most powerful phase shifter ever.

A Emer­gency Call ist recieved

Amprion is one of four trans­mis­sion grid oper­a­tors in Germany. The cata­lyst for building the giant phase shifter, and the asso­ci­ated ground­breaking devel­op­ments, was an emer­gency call. A few years ago, the German Federal Network Agency contacted Amprion with the request to install high-end phase shifters at over­loaded nodes as quickly as possible. Because a study had confirmed what many suspected at the time: Expan­sion of the power grids in Germany is not keeping pace with the increased supply of renew­able energy.

At dimen­sions of 30 x 26 x 11 meters, this device is as large as five single-family houses, and it has a weight of 935 metric tons—this gigantic phase shifter will pay for

Rein­hard Bradt, who is in charge of grid projects at Amprion, goes into more detail. “This can result in indi­vidual maximum-voltage trans­mis­sion lines becoming over­loaded when energy is trans­ferred from offshore wind parks in northern Germany, for example, to the consump­tion centers in southern Germany.” Gigantic phase shifters will help keep the grid durable and powerful, on an ad hoc basis, until grid expan­sion catches up by 2030. However, two condi­tions must be met to avoid dotting the land­scape with expen­sive emer­gency solu­tions: “Invest­ments should amor­tize within three years and should be sustain­able.”

Turbo for the VACUTAP®

A phase shifter is like a two-way valve for the grid that deter­mines whether the current flows from left to right or from right to left. Using this device, grid oper­a­tors can relieve the load on lines without having to inter­vene in power consump­tion or produc­tion, since that would result in hefty redis­patching fees. While a phase shifter cannot increase the overall trans­mis­sion capacity of the grid, it can move the load within the grid to ensure better utiliza­tion until expan­sion can increase the grid’s overall trans­mis­sion capacity.

A master­piece

The first and most powerful VACUTAP® tap changer in the world for high-perfor­mance appli­ca­tions.

The VACUTAP® Advanced Flux Control System ensures the func­tion of vacuum inter­rupters in case of extreme currents and magnetic fields in high-end appli­ca­tions.

18—35 oper­ating posi­tions are possible with the R selector. TheAGIS® (Active Gas Inhi­bi­tion System)makes it possible to reduce gas forma­tion by 90 percent.


The high­lights at a glance:

10,000 kVA switching capacity**

The record tap-changer is up to4 Meters high*

3,200 Ampere rated current*

6,000 Volt step voltage*


Doubled power range for VACUTAP® on-load tap-changer:

*The figures depend on the design and indi­cate the respec­tive maximum values.

Amprion commis­sioned Siemens Energy with the construc­tion of the first mega phase shifter. It will boast the following features: 400 kilo­volt rated voltage, 2,000 mega­volt-ampere throughput capacity and 2,992 ampere rated current. But what still wasn’t clear was how oper­a­tors should perform switching oper­a­tions when such loads are present.

Bradt consid­ered the two conditions—amortization in three years and sustainability—and reasoned that he needed main­te­nance-free on-load tap-changers, meaning those with vacuum tech­nology. The down­side was that there were no such on-load tap-changers in this power rating class. “So we asked MR to develop a VACUTAP for this purpose.” And MR was not fully unpre­pared to confront this chal­lenge since this type of VACUTAP had already been in prelim­i­nary devel­op­ment for years. But once it became much more of a reality, MR started focusing all its energy and working at full force to get the new, mighty VACUTAP ready for oper­a­tion.

Devel­op­ment no longer an winding road

The rated-current limit for VACUTAP tech­nology was previ­ously at 1,300 amperes without forced current split­ting. MR engi­neers worked to raise this limit to a tremen­dous 3,200 amperes within a very short time, surpassing even the 3,000 ampere limit currently applic­able to high-main­te­nance oil tech­nology. The people at MR have devel­oped a special gadget—the Advanced Flux Control System—to manage the high levels of current and the magnetic fields in the on-load tap-changers.

The phase shifter will become a prof­itable invest­ment over the first three years and will continue to operate main­te­nance-free for another 50 years.

Now, nothing stands in the way of the planned, giant phase-shifter trans­former. But how gigantic does it need to be? Here, MR had a nice surprise ready for Siemens and Amprion: The new VACUTAP does not feature any current split­ting. The on-load tap-changer can carry all the current within one sector, which has major conse­quences for the trans­former design because the manu­fac­turer does not need to install a compli­cated winding that takes up a lot of space on the coils, which them­selves are the size of a VW bus. This allowed Siemens to think simpler and smaller. Due to this VACUTAP feature alone, the phase­shifter trans­former is substan­tially smaller than the versions with current split­ting. Smaller means less mate­rial, lighter, and less insu­lating oil. Simply put: more afford­able.

Rein­hard Bradt, Head of Grid Projects at Amprion

And it is easier to trans­port. Ship­ping such a gigantic device on land can only be done using trains, for which there are weight and size limits that need to be observed for the trans­port goods. However, this is not a problem for this slim giant.

Money througRe­dis­patching

One ques­tion remains: How can such a high-tech hunk amor­tize in no more than three years? The answer is surprising: through saved redis­patching costs. In the Euro­pean grid, espe­cially in Germany, many redis­patching measures can be traced back to contrac­tual agree­ments that stip­u­late who can consume and supply how much elec­tricity and when they can do so. These agree­ments are defined down to the minute, and every minute over or under the defined time limits results in enor­mous contrac­tual penal­ties. With phase shifters at the right interfaces—usually on the borders between coun­tries or supply areas—Amprion can carry out all of these contrac­tual measures easily and promptly.

“We expect savings of one hundred million euros over the next three years.”

Rein­hard Bradt, Head of Grid Projects at Amprion

Rein­hard Bradt says, “Use simu­la­tions at a suit­able loca­tion showed savings of more than one hundred million euros after deduc­tion of the invest­ment costs arising over the first three years of oper­a­tion.” Commis­sioning is sched­uled for 2023. The phase shifter will become a prof­itable invest­ment within the first three years and will then continue to operate main­te­nance-free for another 40 to 50 years. Bradt adds, “Using this device will make sense for opti­mizing the power flow near the borders in the Amprion grid even after the ongoing grid expan­sion is completed.”


The first vacuum tap changer for all high-end appli­ca­tions:

  • HVDC trans­formers for long elec­tricity high­ways
  • Vari­able shunt reac­tors (VSR) for reac­tive power compen­sa­tion
  • Phase-shifter trans­formers (PST) for active control of power flowin energy grids
  • Indus­trial trans­formers for high-perfor­mance appli­ca­tions


If you have any ques­tions about VACUTAP® VRL®,
please contact Chris­tian Hillinger: