A Question of Distribution

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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.

CONTROLLING THE VOLTAGE

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 END OF THE ONE-WAY STREET

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.

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.”

SUNSHINE OVER BAVARIA

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.”

ADDITIONAL BANDWIDTHS

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.”

THE NEW STANDARD

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.”

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.”

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IHR ANSPRECHPARTNER

Do you have ques­tions about the pos­si­ble uses of the VRDT?
Fran­co Piz­zut­to is here to help:
 f.pizzutto@reinhausen.com