Municipal Energy TransitionThe little one for the big transition

The world’s small­est high-speed resis­tance tap chang­er for volt­age reg­u­la­tion dis­tri­b­u­tion trans­form­ers has two huge tal­ents for the ener­gy tran­si­tion.


Expanding networks quickly and cost-effectively

The high­er the share of renew­able ener­gies fed into the grid, the high­er the degree of nec­es­sary grid expan­sion. This is because with a lot of wind and solar pow­er, volt­age fluc­tu­a­tions in the dis­tri­b­u­tion net­work increase sharply.

Each coun­try has dif­fer­ent toler­ances for volt­age fluc­tu­a­tions. These vary from plus/minus five to ten per­cent. Guar­an­tee­ing these tol­er­ances is becom­ing more dif­fi­cult for grid oper­ators as the share of renew­ables in­creases. The solu­tion: grid expan­sion. But there are two approach­es to this. First, the com­plex and cost-inten­sive expan­sion with thick­er lines and more local net­work sta­tions. Sec­ond, the more cost-effec­tive, flex­i­ble expan­sion using volt­age reg­u­la­tion dis­tri­b­u­tion trans­form­ers, so-called VRDTs. With the lat­ter, the final con­trol point moves from the sub­sta­tion to the local net­work sta­tion which makes it eas­i­er to keep the volt­age sta­ble, because the grid gets more inter­me­di­ate con­trol points that reg­u­late close to the source. For such approach­es, the ECOTAP® VPD® on-load tap-chang­er can be inte­grat­ed into exist­ing trans­former designs with lit­tle effort—no new lines or build­ings are required. Replac­ing an exist­ing unreg­u­lat­ed local trans­former with a reg­u­lat­able one takes about one day. A com­plete line upgrade would take months.

Increased capacities

How­ev­er, ECOTAP® VPD® not only favors the ener­gy turn­around through its increased absorp­tion capac­i­ty for renew­able gen­er­a­tors in the dis­tri­b­u­tion grid. With the tri­umphant advance of elec­tro­mo­bil­i­ty, the load-side demands on the grids will also increase mas­sive­ly. In this case, too, grid oper­a­tors will ben­efit from the increased absorp­tion ca­pacity of the grids due to the VRDT.

The minia­ture on-load tap-chang­er ECOTAP® VPD® makes all dis­tri­b­u­tion trans­form­ers con­trol­lable. It is avail­able as a sin­gle-phase ver­sion (9 oper­at­ing set­tings) or as three-phase with or as with­out pre­s­e­lec­tor (9 or 17 oper­at­ing set­tings). Func­tion­al­i­ty in a small space: The motor mod­ule (top part) reli­ably dri­ves the on-load tap-chang­er (low­er part). This actu­ates the selec­tor as well as the on-load tap-chang­er with a tran­si­tion resis­tor and vac­u­um inter­rupter.


Ten percent more power from wind and solar

Wind tur­bine or open-space pho­to­volta­ic pow­er plants require local con­vert­ers that con­vert DC volt­age into AC volt­age for grid feed­ing. The per­for­mance of a con­vert­er is defined by the amount of max­i­mum cur­rent and the applied grid volt­age. Since the volt­age can fluc­tu­ate, man­u­fac­tur­ers of wind and PV sys­tems must base the per­for­mance on a volt­age val­ue. Usu­al­ly, this is the nom­i­nal volt­age val­ue or less—but nev­er the volt­age opti­mum. This is why the appar­ent pow­er that an invert­er can pro­vide is large­ly depen­dent on grid fluc­tu­a­tions. This can lead to the sit­u­a­tion that in oper­a­tion the fed-in active power—and only this is usu­al­ly paid for! — is low­er than what the ener­gy source would pro­vide in the case of strong wind or strong solar radi­a­tion. Unwant­ed active pow­er reduc­tions can have anoth­er cause such as when the grid volt­age fluctu­ates and the reac­tive pow­er demand of the grid turns out to be so high that, togeth­er with the active pow­er pro­vid­ed, it exceeds the appar­ent pow­er capac­i­ty of the invert­er. Until now, in such cas­es one could either throt­tle the valu­able active pow­er or pro­vide cost­ly but most­ly unused reserve con­vert­er pow­er and reac­tive pow­er sources.

Inverter transformers

The cheap­er solu­tion to get every­thing out of the plants is to replace the trans­form­ers on the invert­ers with reg­u­lat­ed trans­form­ers. They reg­u­late the volt­age so that it is opti­mal for the invert­er and ensure that the max­i­mum active pow­er can be fed in at every oper­at­ing point. The result: up to ten per­cent more usable pow­er from wind and PV—according to plan and cer­ti­fi­able. With the ECOTAP® VPD® mini on-load tap-chang­er, the basic design of VRDTs can remain unchanged. This is an advan­tage for wind pow­er plants, for exam­ple, where the trans­former sits direct­ly in the nacelle. and vol­ume and weight play a cen­tral role. Oth­er en­er­gy-tran­si­tion plants with con­vert­ers also ben­e­fit from the pow­er boost pro­vid­ed by low-cost, con­trol­lable trans­form­ers: for exam­ple, urgent­ly need­ed bat­tery stor­age sys­tems or elec­trolyz­ers for hydro­gen pro­duc­tion.


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