Record Power in China

China’s econ­o­my is grow­ing rapid­ly, as is the resul­tant demand for more and more elec­tric­i­ty to sus­tain its glis­ten­ing megac­i­ties. To help the metrop­o­lis­es become clean­er, even more ener­gy is set to be gen­er­at­ed from renew­able resources in the future. But the favor­able con­di­tions need­ed to gen­er­ate this ener­gy are found far away from the urban areas in the east. Instead, they are found in the sparse­ly pop­u­lat­ed west­ern part of the coun­try, such as in the province of Xin­jiang, where it is very windy and there are many hours of sun­shine, as well as numer­ous rivers to gen­er­ate hydropow­er. The chal­lenge is to trans­port this ener­gy over a large dis­tance to where it is need­ed, while keep­ing loss­es to a min­i­mum.

Transporting electrical energy over long distances

The solu­tion to this chal­lenge is high-volt­age direct-cur­rent (HVDC) trans­mis­sion. To enable elec­tric­i­ty to be trans­port­ed over large dis­tances with the low­est pos­si­ble loss­es, the pow­er must be trans­mit­ted with a low cur­rent and high trans­mis­sion volt­age. For long trans­mis­sion paths, this is most eco­nom­i­cal with direct cur­rent. There­fore, at the begin­ning of the HVDC trans­mis­sion line, the alter­nat­ing cur­rent is trans­formed into direct cur­rent in a con­vert­er sta­tion and then trans­formed back to alter­nat­ing cur­rent at the end of the line.

There are already numer­ous HVDC lines in oper­a­tion around the world, but the new line that con­nects the city of Changji in the Xin­jiang province with Guquan in the Anhui province sur­pass­es all pre­vi­ous records. At 3,284 kilo­me­ters long, it will have a trans­mis­sion capac­i­ty of twelve gigawatts when it is con­nect­ed to the grid, which is expect­ed to take place at the end of 2018. This rough­ly cor­re­sponds to the pow­er of twelve con­ven­tion­al large pow­er sta­tions. 1,100 kilo­volts of direct-cur­rent volt­age is required for this trans­mis­sion. By way of com­par­i­son, the high­est trans­mis­sion capac­i­ty to date is eight gigawatts over a dis­tance of
2,210 kilo­me­ters with a trans­mis­sion volt­age of 800 kilo­volts.

Superlative transformers

The Chi­nese ener­gy com­pa­ny “State Grid Cor­po­ra­tion of Chi­na” com­mis­sioned Siemens to design 28 trans­form­ers for the con­vert­er sta­tion at the end of the new line in Guquan. The trans­form­ers, which were man­u­fac­tured at two Siemens sites and two part­ner plants in Chi­na, have set a new record as well: Each of the sev­en 1,100 kilo­volt DC sin­gle-phase trans­form­ers is 37.5 meters long, 14.5 meters high, twelve meters wide, and weighs 909 met­ric tons when in oper­a­tion. With a trans­mis­sion capac­i­ty of 587.1 mega­volt-amperes each, they are the most pow­er­ful HVDC trans­form­ers in the world. This lev­el of pow­er places enor­mous demands on the trans­form­ers and on the reli­a­bil­i­ty of the tech­nol­o­gy.

If the pow­er should fail, mil­lions of peo­ple would be with­out elec­tric­i­ty. When it came to the on-load tap-chang­ers, Siemens there­fore used the VACUTAP^® VR^® from Maschi­nen­fab­rik Rein­hausen (MR). Silke Schwarzwälder, Port­fo­lio Man­ag­er for tap chang­ers at MR, explains: “The vac­u­um on-load tap-chang­er VACUTAP^® VR^® is the most suit­able option for the extra-high-volt­age range and there­fore for HVDC appli­ca­tions. It is also very depend­able in oper­a­tion.” The VACUTAP^® Advanced Arc Con­trol Sys­tem enables the reli­able quench­ing of the switch­ing arc and the VACUTAP^® Step Pro­tec­tion Sys­tem^® offers pro­tec­tion against over­volt­ages.

Anoth­er advan­tage is that the VACUTAP^® VR^® is extreme­ly eco­nom­i­cal, as it is capa­ble of per­form­ing 300,000 tap-change oper­a­tions with­out any main­te­nance. The divert­er switch insert can be used for 1.2 mil­lion tap changes before need­ing to be replaced. “The con­vert­er sta­tions are locat­ed in very remote regions, which means that they need to be low-main­te­nance,” explains Schwarzwälder.

The longest bushings in the world

The vast trans­former dimen­sions also pre­sent­ed oth­er sup­pli­ers with enor­mous chal­lenges. This includ­ed the glob­al mar­ket leader in high-volt­age bush­ings – HSP Hochspan­nungs­geräte GmbH from the Ger­man city of Cologne. Mar­cus Cramer von Claus­bruch, Region­al Sales Man­ag­er at HSP, describes the scale of the project: “We built a sep­a­rate plant to pro­duce the 1,100 kilo­volt DC bush­ings, as the exist­ing hall was too small.” The bush­ings pro­duced by HSP for the HVDC trans­form­ers are 19 meters long and weigh 15.5 met­ric tons. Yet anoth­er record! These are the longest and heav­i­est trans­former bush­ings on the mar­ket to date.

„There are not many com­pa­nies that can pro­duce hol­low insu­la­tors of 15 meters in length.“Mar­cus Cramer von Claus­bruch, Region­al Sales Man­ag­er at HSP

“With AC volt­age, these kinds of bush­ings only weigh one met­ric ton,” explains Cramer von Claus­bruch. HSP is one of the few com­pa­nies any­where in the world that can pro­duce bush­ings in such large dimen­sions using resin tech­nol­o­gy. The sol­id active com­po­nent con­sists of resin-impreg­nat­ed paper (RIP), which means that the bush­ing is free from oil. “This require­ment was stip­u­lat­ed by Chi­na, as oil is too high a risk fac­tor when used with these com­po­nents for extra-high-volt­age appli­ca­tions.” For the insu­la­tion, HSP used hol­low com­pos­ite insu­la­tors with shield­ing from Rein­hausen France SAS. “There are not many com­pa­nies that can pro­duce hol­low insu­la­tors of 15 meters in length which also sat­is­fy the demand­ing spec­i­fi­ca­tions,” explains Cramer von Claus­bruch.

Along­side the insu­lat­ing prop­er­ties, pro­tec­tion against earth­quakes was also an impor­tant require­ment. “We’re talk­ing about 1,200 kilo­volts here. If that goes bang, then you real­ly know about it!” To pre­vent this from hap­pen­ing, HSP has test­ed the bush­ings exten­sive­ly. “Even the rou­tine pro­gram on a bush­ing takes five days,” says Cramer von Claus­bruch. The Region­al Sales Man­ag­er sees great poten­tial for the future of such appli­ca­tions: “The gen­er­a­tion and trans­mis­sion of large quan­ti­ties of ener­gy is grow­ing in sig­nif­i­cance all over the world.”