The problem: where to put reactive power?

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There are rum­bling and hiss­ing nois­es in the pro­duc­tion hall in Unter­wellen­born, Thuringia where enor­mous forces are at work when the 1,250-degree, glow­ing red steel blocks are dri­ven back and forth through the rolling mill until they have the desired thick­ness and shape. Stahlw­erk Thürin­gen GmbH (SWT) pro­duces more than 800,000 tons of steel per year, which is used world­wide in the con­struc­tion indus­try, for bridges and rail­ways, but also in off­shore wind farms. To meet the var­i­ous require­ments, SWT has over 250 dif­fer­ent profiles in its range, all of which are made from 100-per­cent recy­cled scrap.

The large dri­ves that pro­pel the steel through the rollers per­form heavy-duty work, which also affects the pow­er grid—at least if SWT does not take pre­ven­ta­tive action. Prob­lems may arise since the motors need sub­stan­tial reac­tive pow­er to man­age ongo­ing accel­er­a­tion, brak­ing, and changes in direc­tion. Added to this are har­mon­ics gen­er­at­ed by the oper­a­tion of pow­er­ful speed-con­trolled rolling mill dri­ves.

Since too much reac­tive pow­er and har­mon­ics over­load the pow­er grid and make it unsta­ble, ener­gy sup­pli­ers set lim­its that large indus­tri­al con­sumers are not allowed to exceed, with vio­la­tions result­ing in con­sid­er­able costs. Com­pa­nies such as SWT must there­fore take mea­sures to ensure that they do not feed too much of these dis­rup­tive fac­tors into the grid. Until now, SWT has relied on an SVC (sta­t­ic var com­pen­sator) sys­tem with filter cir­cuits and a thyris­tor-con­trolled reac­tor (TCR) to pro­vide capac­i­tive and induc­tive reac­tive pow­er, and filter out har­mon­ics. To remain pre­pared for the future, inno­v­a­tive solu­tions were con­sid­ered to bet­ter meet upcom­ing require­ments.

Efficient STATCOM system

When col­leagues from MR’s Pow­er Qual­i­ty Projects depart­ment pre­sent­ed a con­cept for a new STATCOM sys­tem at SWT, it came at just the right time. STATCOM (sta­t­ic syn­chro­nous com­pen­sator) is a sys­tem for dynam­ic reac­tive pow­er con­trol in elec­tri­cal pow­er trans­mis­sion sys­tems. It belongs to the FACTS (flex­i­ble AC trans­mis­sion) fam­i­ly of sys­tems or plants which were devel­oped to improve the sta­bil­i­ty, effi­cien­cy, and flex­i­bil­i­ty of pow­er grids. The main advan­tage of STATCOM sys­tems is that they react much faster than an SVC plant and do not require filter cir­cuits, which results in sig­nifi­cant­ly few­er loss­es. Thomas Rösel­er, Head of Inno­va­tion and Projects at MR Pow­er Qual­i­ty: “We devel­oped our GRIDCON^® STATCOM MMC sys­tem specifi­cal­ly for indus­tri­al plants. This is because prob­lems such as those encoun­tered at the SWT steel­works arise wher­ev­er ener­gy is dynam­i­cal­ly con­vert­ed.” SWT is the first cus­tomer to use this solu­tion, with the new sys­tem sched­uled to go into oper­a­tion in mid-2026. Addi­tion­al poten­tial appli­ca­tions include elec­trol­y­sis, min­ing, and trac­tion pow­er sup­ply.

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Even more areas of application

Steel mills are not alone in fac­ing these problems—wherever elec­tri­cal ener­gy is dynam­i­cal­ly con­vert­ed, grid sta­bi­liza­tion mea­sures are nec­es­sary. The GRIDCON^® STATCOM MMC sys­tem can also help in the fol­low­ing appli­ca­tions:

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The path to a STATCOM system

With the GRIDCON^® STATCOM MMC sys­tem, MR Pow­er Qual­i­ty offers a stan­dard­ized solu­tion that can be imple­ment­ed with­in a year with min­i­mal plan­ning effort: