Established standard

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A ver­i­ta­ble solar ener­gy boom began in Ger­many in 2009 as the price of solar mod­ules fell due to the finan­cial cri­sis, and gov­ern­ment sub­si­dies became even more attrac­tive. So when more and more peo­ple decid­ed to turn their own roof into a pow­er plant, all eyes sud­den­ly turned to the low-volt­age grids, because with the many decen­tral­ized feed­ers, it became increas­ing­ly dif­fi­cult to main­tain the volt­age band. The pow­er con­sump­tion could have been improved, for exam­ple, by lay­ing new and thick­er cables and build­ing addi­tion­al trans­former sta­tions in the local grid.

How­ev­er, this is not only an expen­sive process, but also a lengthy one due to the many approval pro­ce­dures. Experts there­fore came up with a dif­fer­ent idea: Why not make the local grid trans­form­ers con­trol­lable and in that way increase the grid’s capac­i­ty? What didn’t exist at the time, how­ev­er, were suit­able on-load tap-chang­ers that could be used sen­si­bly to reg­u­late the volt­age of such trans­form­ers. The per­fect task for MR, the inven­tor of the first on-load tap-chang­er based on the resis­tance prin­ci­ple! Fran­co Piz­zut­to, Busi­ness Devel­op­ment Man­ag­er, remem­bers: “In the first pilot projects, we exper­i­ment­ed with con­ven­tion­al on-load tap-chang­ers in order to gain expe­ri­ence” (see also the inter­view with Fran­co Piz­zut­to).

We real­ized, how­ev­er, that this could not be a per­ma­nent solu­tion, because if a volt­age reg­u­lat­ing dis­tri­b­u­tion trans­former (VRDT) was to be used on a large scale, it had to be afford­able and could not exceed the foot­print of a con­ven­tion­al dis­tri­b­u­tion trans­former. In 2012, the GRIDCON® iTAP® was the first tap-chang­er for dis­tri­b­u­tion trans­form­ers to be launched on the mar­ket, and in 2016, the ECOTAP® VPD® marked a deci­sive mile­stone: It was the world’s small­est on-load tap-chang­er to date and took the VRDT to a new lev­el.

Today, around 15 years after the first solar boom,the the ten thou­sandth ECOTAP® VPD® has already been installed in VRDTs around the world. While the main focus of use has so far been Cen­tral Europe, more and more coun­tries around the world are also dis­cov­er­ing the VRDT for them­selves. Such as in the USA, for exam­ple, where MR has devel­oped the ECOTAP® VPD® I, a solu­tion that also makes pos­si­ble the reg­u­la­tion of sin­gle-phase grids (see arti­cle about Sin­gle-phase volt­age reg­u­lat­ing dis­tri­b­u­tion trans­form­ers in the USA). How­ev­er, even if the VRDT can now be seen as a stan­dard oper­at­ing device, there are still reser­va­tions. In the fol­low­ing, three grid oper­a­tors and three trans­former man­u­fac­tur­ers pro­vide insights into how they use VRDTs and what they appre­ci­ate about them.

100 percent VRDT at Avacon

“We pro­cure one hun­dred per­cent of our new trans­form­ers as VRDTs since we assume that we need almost a one-hun­dred per­cent quo­ta in the grid area any­way,” says Bian­ca Ren­ner from Ava­con Netz GmbH, who is respon­si­ble for low-volt­age strat­e­gy issues in the “Strat­e­gy and Inno­va­tion” depart­ment. Ava­con is one of the largest region­al dis­tri­b­u­tion grid oper­a­tors in Ger­many with a grid area that stretch­es from the North Sea coast to south­ern Hesse and sup­plies almost two and a half mil­lion peo­ple with elec­tric­i­ty. Ava­con played a key role in the devel­op­ment of the VRDT and par­tic­i­pat­ed in pilot stud­ies from the very begin­ning. “Essen­tial­ly, we use VRDTs to decou­ple the low and medi­um volt­ages and also to sig­nif­i­cant­ly reduce cable net­work expan­sion,” says Ren­ner. Over 90,000 decen­tral­ized gen­er­a­tion plants with a total out­put of almost 14 gigawatts are already con­nect­ed today. And this fig­ure is set to rise.

In addi­tion, the elec­tri­fi­ca­tion of the heat­ing and trans­port sec­tors is adding more and more new con­sumers. “If we have to expand the grid on a large scale, then the res­i­dents in a set­tle­ment should notice as lit­tle as pos­si­ble. So we can’t just dig up every street and build pow­er lines,” empha­sizes Ren­ner. Espe­cial­ly as there is a lack of man­pow­er to car­ry out this amount of work. She there­fore prefers a point­ed mea­sure such as the VRDT as a quick and effi­cient alter­na­tive. Inter­nal­ly, how­ev­er, it is impor­tant to get the employ­ees on board: “We have found that accep­tance comes with expe­ri­ence,” says Ren­ner.

EAM relies on large-scale deployment

Mar­vin Reit­ing, Head of Asset Man­age­ment at EAM Netz GmbH, has a sim­i­lar view. “It is impor­tant for the employ­ees to gain expe­ri­ence first,” he says. But they were gen­er­al­ly pos­i­tive: “The fact that it doesn’t involve a lot of work meant that there was a high lev­el of accep­tance straight away. The VRDT was con­vinc­ing.” EAM Netz GmbH sup­plies around 1.4 mil­lion peo­ple in Hesse and the neigh­bor­ing fed­er­al states with elec­tric­i­ty and 43,500 decen­tral­ized gen­er­a­tion plants are cur­rent­ly con­nect­ed in the grid area.

EAM first used a VRDT in 2009, pri­mar­i­ly because of the PV sys­tems at the low volt­age lev­el, but the com­pa­ny now also uses them exten­sive­ly at medi­um volt­age. Reit­ing is extreme­ly sat­is­fied with the equip­ment: “It’s a stan­dard prod­uct which is absolute­ly reli­able and can be com­pared with a con­ven­tion­al trans­former.” The grid oper­a­tor now pro­cures around a third of its new trans­form­ers as VRDTs and Reit­ing assumes that this share will increase. In the last three years in par­tic­u­lar, the num­ber of new­ly con­nect­ed PV sys­tems has sky­rock­et­ed, mean­ing that the deploy­ment strat­e­gy has also changed: “We tend to mon­i­tor our grid on a large scale and no longer check indi­vid­ual cas­es,” says Reit­ing.

Kärnten Netz gets on board

Kärn­ten Netz GmbH in Aus­tria, on the oth­er hand, still relies on a case-by-case assess­ment. Nev­er­the­less, Michael Pink, respon­si­ble for grid plan­ning, also sees the VRDT as a stan­dard tool for grid devel­op­ment. While the com­pa­ny gained its first expe­ri­ence in 2012, the need for fur­ther use of reg­u­lat­ed local sub­sta­tions was not yet giv­en at that time, so it remained a pilot project.

This changed at the end of 2020 as more and more of the 235,100 cus­tomers sup­plied with elec­tric­i­ty by Kärn­ten Netz decid­ed to install solar sys­tems, with the main impe­tus being pro­vid­ed by the Renew­able Ener­gy Expan­sion Act (EAG), which the Aus­tri­an gov­ern­ment passed to increase the share of renew­able ener­gy in elec­tric­i­ty pro­duc­tion to 100 per­cent by 2030. This act stip­u­lates that every cus­tomer has the right to feed into the grid and that grid oper­a­tors were oblig­ed to expand the grid with­in one year. “So we made a fresh start,” says Pink. How­ev­er, the VRDT is not the best solu­tion every­where in Kärnten’s sup­ply area: “We have very wide grid spurs where the volt­age qual­i­ty and short-cir­cuit pow­er are very low,” says Pink. For this rea­son, Kärn­ten Netz still relies on a mix­ture of con­ven­tion­al grid expan­sion and VRDTs.

The view of transformer manufacturers

And what do trans­former man­u­fac­tur­ers say? Säch­sisch-Bay­erische Stark­strom-Geräte­bau GmbH (SBG) is a lead­ing man­u­fac­tur­er of dis­tri­b­u­tion trans­form­ers and has been a VRDT man­u­fac­tur­er from the very begin­ning, con­tribut­ing its expe­ri­ence and exper­tise to the devel­op­ment right from the start. Michael Büh­n­ert, Head of Sales at SBG, explains: “From the manufacturer’s point of view, I can say that we have a very good and mature prod­uct today that can be installed almost plug and play.”

Most of SBG’s cus­tomers, to whom it has sold more than 4,000 VRDTs, are ener­gy sup­pli­ers, but Büh­n­ert also sees anoth­er impor­tant area of appli­ca­tion that many cus­tomers have not yet real­ly con­sid­ered: in-com­pa­ny grids: “Sta­ble volt­age is extreme­ly impor­tant, espe­cial­ly where you are deal­ing with sen­si­tive process­es, con­trol sys­tems, or reg­u­la­tion or elec­trol­y­sis process­es.”

In Poland, Olek­san­dr Dat­siuk, Area Sales Man­ag­er at Hitachi Ener­gy, is very famil­iar with the demand for VRDTs: “In recent years, the num­ber of devices ordered has increased many times over as more and more cus­tomers are opt­ing for this type of solu­tion.” The main sales region is Cen­tral Europe, where 70 per­cent of VRDTs are installed.

Hitachi has now sold more than 3,500 trans­form­ers with the ECOTAP® VPD® and cus­tomers, pri­mar­i­ly ener­gy sup­pli­ers, are sat­is­fied: “We haven’t had any major com­plaints, which speaks vol­umes for the high qual­i­ty.” Inte­gra­tion into the exist­ing pro­duc­tion oper­a­tion was also quite sim­ple thanks to the good coop­er­a­tion with MR. “The on-load tap-chang­er is sup­plied ready for instal­la­tion and con­nec­tion, which speeds up the pro­duc­tion process­es,” says Dat­siuk.

Ibrahim Gülay can report equal­ly good expe­ri­ences thou­sands of kilo­me­ters fur­ther south. He is Elec­tri­cal Design Ten­der­ing Leader at BEST, the largest trans­former man­u­fac­tur­er in Turkey. Since 2020, BEST has sold 86 VRDTs for 36 dif­fer­ent projects. “Most of these projects are in the tex­tile indus­try,” notes Gülay. Cus­tomers are pri­mar­i­ly EPCs that plan the sys­tems for com­pa­nies in Cen­tral Asia where they need VRDTs because of the unsta­ble grid volt­age.

How­ev­er, BEST has also built VRDTs for waste­water treat­ment plants in Turkey, oil and gas projects in Iraq, and min­ing projects in Africa. Before the ECOTAP® VPD® was avail­able, the only option was to use a medi­um-sized pow­er trans­former. “As a design­er of dis­tri­b­u­tion trans­form­ers, I am very grate­ful to MR for this inno­va­tion. Now it is pos­si­ble to pro­duce a VRDT with the size and weight of a stan­dard dis­tri­b­u­tion trans­former,” says Gülay.

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Technology from the pioneer

MR played a key role in the devel­op­ment of the VRDT.

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