A Ques­tion of Distri­b­u­tion

Unreg­u­lated distri­b­u­tion networks are still the norm around the world. However, the disad­van­tages are evident every day in emerging markets as well as in indus­trial centers. The future belongs to regu­lated distri­b­u­tion trans­formers.

It’s touch and go every day: Will the voltage remain stable? Or is today the day when it happens? Network oper­a­tors, indus­trial consumers, energy suppliers and trans­former manu­fac­turers world­wide are familiar with these concerns: They are all faced with the chal­lenge of main­taining a stable voltage in the precar­i­ously balanced medium- and low-voltage networks and of securing an optimal voltage band—today, and in the future. It all revolves around the ques­tion: What is the role of distri­b­u­tion network trans­formers in this situ­a­tion?

One thing is clear: everyone wants a stable voltage band. But the causes of voltage prob­lems often differ funda­men­tally from one country to the next: On the one hand, suppliers in the highly devel­oped indus­trial coun­tries are strug­gling with the inte­gra­tion of renew­able ener­gies. On the other hand, many econom­i­cally weaker coun­tries are faced with networks with a tight short-circuit capacity, long trans­mis­sion distances, and volatile consumers and gener­a­tors.


Jorge Leiva, who is respon­sible for research and devel­op­ment at the Argen­tinean trans­former manu­fac­turer TTE in Córdoba, is currently inves­ti­gating how the inte­gra­tion of the new ECOTAP VPD on-load tap-changer from Maschi­nen­fabrik Rein­hausen (MR) influ­ences the design of distri­b­u­tion trans­formers. Together with his colleague Pablo Arras­caeta and a team of engi­neers, he is currently devel­oping a proto­type.

“With VRDTs, we can manage volatile supply, load fluc­tu­a­tions, and feed-ins from decen­tral­ized gener­a­tors.” Jorge Leiva, TTE, Buenos Aires

Although energy consump­tion is contin­u­ally increasing in this South Amer­ican nation, oper­a­tors are lagging behind consid­er­ably with the expan­sion of their networks. This results in high voltage fluc­tu­a­tions, which regu­larly lead to equip­ment damage and faults in produc­tion processes. TTE devel­oper Leiva explains: “Since we are also affected by the volatile voltage, we will use the proto­type to supply stable voltage to our test facil­i­ties for the trans­formers that are produced on site. This means that, in addi­tion to regu­lated trans­formers, we can also demon­strate reli­able tests to our customers.” Franco Pizzutto, Busi­ness Devel­op­ment Manager at MR, sees the protec­tion of indus­trial processes as an appli­ca­tion area with great poten­tial: “Voltage regu­lated distri­b­u­tion trans­formers (VRDTs) with ECOTAP VPD can benefit all those who operate their own distri­b­u­tion network and need to control sensi­tive processes with volatile medium voltage such as, for example, indus­trial compa­nies or hospi­tals.”

Although renew­able ener­gies such as solar power or wind farms still play a minor role in Argentina, the Ministry of Energy and Mining is already gener­ating signif­i­cant momentum for growth. This primarily concerns farms above the ten-megawatt class. TTE devel­oper Leiva, however, is expecting new network connec­tion guide­lines, which will also allow decen­tral­ized gener­a­tors with smaller power outputs to connect to the network. “In such an envi­ron­ment, regu­lated distri­b­u­tion trans­formers can perform to their full poten­tial and manage the prob­lems of volatile supply, load fluc­tu­a­tions, and feed-ins from decen­tral­ized gener­a­tors.”


The situ­a­tion is different in highly devel­oped indus­trial coun­tries, which are already a step ahead in terms of renew­able ener­gies. The chal­lenge for distri­b­u­tion networks here has less to do with the large wind and solar farms that are found, for example, in Spain, as these transfer the recov­ered energy directly to the high-voltage networks. Instead, it is the small and extra-small decen­tral­ized feeders at the medium- and low-voltage levels which cause partic­ular prob­lems for suppliers because the distri­b­u­tion networks have been designed as one-way streets. In Germany, however, the networks are now char­ac­ter­ized by rapid two-way traffic, as the German legis­la­ture wants at least 80 percent of the power supply to be covered by renew­able ener­gies by 2050 at the latest.

Distri­b­u­tion networks were designed as one-way streets, but they are now char­ac­ter­ized by rapid two-way traffic. VRDTs ensure a stable voltage band. (© SBG)

In the last few years, generous subsi­dies have created a boom in wind power, biogas and photo­voltaic plants (PV) – with impres­sive figures: Over 1.5 million solar plants now supply more than six percent of the German elec­tricity require­ment. And the trend is rising. According to the Fraun­hofer Insti­tute for Solar Energy Systems, more than 98 percent of the solar power plants in Germany are connected to the regional decen­tral­ized low-voltage network. In many regions, more elec­tricity is gener­ated than consumed on sunny days. The load flow then turns around and the gener­a­tion-driven energy recovery signif­i­cantly exceeds the orig­inal refer­ence power for a while. The networks reach their intake limits, and voltage fluc­tu­a­tions occur.

However, large-scale suppliers, such as Avacon AG and Bayern­werk AG, which belong to the E.ON Group, must guar­antee a voltage band of plus/minus ten percent, while at the same time contin­u­ally connecting addi­tional renew­able energy providers. Franco Pizzutto brings the VRDT into play: “Since 2008, we have been working with trans­former manu­fac­turers and network oper­a­tors to research how to support voltage band compli­ance with VRDT. We also focused on the opti­miza­tion of network topolo­gies, and how to reduce or avoid the costs of complex network exten­sion measures.”


The largest regional network oper­ator in Bavaria, Bayern­werk AG, is partic­u­larly affected by the PV boom. On sunny days, the Bavarian company has to accept up to 5,600 megawatts of solar power from more than 255,000 gener­a­tors and trans­port it from the coun­try­side to the cities and other load centers via the low-, medium-, and high-voltage networks. Elec­trical engi­neer Sebas­tian Schmidt is respon­sible for research and devel­op­ment activ­i­ties at Bavaria’s largest large-scale supplier and explains: “We have to antic­i­pate such devel­op­ments. A classic network expan­sion with new cables and addi­tional trans­former stations takes decades, and is corre­spond­ingly cost and labor inten­sive. There­fore, we are always looking for alter­na­tive ways to opti­mize our networks.”

“We’re always looking for alter­na­tives to improve our networks.”Sebas­tian Schmidt, Bayern­werk AG, Bamberg

It is this search that led Bayern­werk AG straight to MR. Schmidt adds: “MR had already estab­lished itself as a reli­able partner in the field of high- and medium-voltage tap-changers, which have made it possible to dynam­i­cally adjust the voltage level, espe­cially in medium-voltage networks that are char­ac­ter­ized by feed-ins. Together, we have worked inten­sively on the devel­op­ment, stan­dard­iza­tion, and use of regu­lated trans­formers for distri­b­u­tion networks within the frame­work of group-wide research projects.”


Bayern­werk affil­iate Avacon AG played a leading role in the devel­op­ment. In addi­tion to the feed-in of solar power, the German large-scale supplier, which is located in the north of Germany and is one of the country’s largest regional energy service providers, focuses on wind energy and biomass plants. Stefan Henssen, who works in the field of distri­b­u­tion network tech­nology, reports addi­tional prob­lems: “Many wind farms feed directly into the medium-voltage networks; at the same time, the distri­b­u­tion networks are becoming increas­ingly volatile. There­fore, we have to manage a fluc­tu­ating supply voltage. The VRDT is ideal for this task, as it decou­ples the medium voltage from the low voltage and creates addi­tional band­widths.”

“With the VRDT, we can stabi­lize a fluc­tu­ating supply voltage.” Stefan Henssen, Avacon AG, Salzgitter

In addi­tion to the tech­nical para­me­ters, the network plan­ners focus primarily on invest­ment and oper­ating costs for all network opti­miza­tion measures. Avacon tech­ni­cian Henssen explains: “In order to be able to replace unreg­u­lated trans­formers with regu­lated trans­formers, we placed special emphasis on longevity and low main­te­nance costs for the tap-changer. The trans­former foot­print could not be changed, which means that the VRDT has to fit into the existing stations for unreg­u­lated trans­formers for a cost-effec­tive exchange.” (For more infor­ma­tion, see the inter­view with trans­former manu­fac­turer SBG on page 14). The Bayern­werk tech­ni­cian Schmidt adds: “It was also impor­tant for us that the tap-changer did not cause any addi­tional losses in the trans­former.”


Avacon exper­i­mented inten­sively with the different possible uses of the VRDT within distri­b­u­tion networks. They researched the effects on network stability, ranging from selec­tive to large-scale use. Bayern­werk devel­oper Schmidt adds: “When used selec­tively, the VRDT has the greatest effect on the down­stream low-voltage network. When used in greater numbers on a feeder basis or in large-scale use, the VRDT can also have a posi­tive effect on the medium-voltage network.”


Regu­lated distri­b­u­tion network trans­formers keep the voltage in distri­b­u­tion networks stable, compen­sate for fluc­tu­a­tions in the medium voltage and respond to changes in feed-in and load at the low-voltage level.

The ECOTAP VPD turns rigid distri­b­u­tion trans­formers into intel­li­gent regu­lating trans­formers. The most impor­tant features of the new tap-changer:

  • Main­te­nance free for up to 500,000 tap changes due to vacuum tech­nology
  • Most compact tap-changer world­wide
  • Suit­able for synthetic and natural esters as insu­lating liquid
  • Large regu­lating range yet fine grading

Find out more about the ECOTAP VPD

Their long-standing research and devel­op­ment work has paid off: VRDTs with ECOTAP VPD are now avail­able as stan­dard equip­ment throughout the entire E.ON Group. They are also avail­able to regional network plan­ners as an impor­tant part of the network opti­miza­tion port­folio. Henssen and Schmidt are there­fore expecting the number of instal­la­tions to grow contin­u­ally over the next few years. MR engi­neer Pizzutto is also convinced that the VRDT will play an increas­ingly impor­tant role. He believes that new types of load will provide a further driving force for the devel­op­ment of networks with control tech­nology: “The trend toward elec­tric mobility is looming. Imagine all the people coming home at the end of the day and wanting to charge their elec­tric cars at the same time. Many networks that do not have access to control tech­nology by then will simply break down.”


Do you have ques­tions about the possible uses of the VRDT?
Franco Pizzutto is here to help: