Everything under control

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It’s a black­out. The pow­er grid is down. The roads are in a state of grid­lock because traf­fic lights have switched off. The water sup­ply has been dis­abled because the pumps are no longer run­ning. Gaso­line pumps stop dis­pens­ing fuel and, after a day goes by, emer­gency pow­er sys­tems in hos­pi­tals begin to fail. Because fuel assem­bly cool­ing in nuclear pow­er plants also requires elec­tric­i­ty, the threat of nuclear dis­as­ter looms.

Such night­mare sce­nar­ios attract a great deal of atten­tion among the pub­lic at large. But it’s not always absolute cat­a­stro­phes that war­rant con­cern. For many indus­tri­al com­pa­nies, every­day fluc­tu­a­tions in volt­age are trou­ble enough—especially when they cause pro­duc­tion down­time or even dam­age to elec­tri­cal sys­tems and pro­duc­tion facil­i­ties. Volt­age fluc­tu­a­tions are a glob­al phe­nom­e­non and are not con­fined to the “weak­er” grids of devel­op­ing nations. Even high­ly devel­oped grids in indus­tri­al­ized coun­tries suf­fer from a grow­ing lev­el of volatil­i­ty. The main cul­prit of these fluc­tu­a­tions in line volt­age is renew­able ener­gy.

The wind doesn’t always blow at the same strength and cloudy weath­er ensures a con­stant­ly vary­ing elec­tric­i­ty stream from solar instal­la­tions. And if major con­sumers of elec­tric­i­ty like alu­mini­um plants start up the smelters, the volt­age drops and can only be com­pen­sat­ed by increas­ing the pow­er in-feed. Anoth­er prob­lem is that mon­i­tor­ing of pow­er grids is only orga­nized at the medi­um-volt­age lev­el. If fluc­tu­a­tions occur in these volt­age ranges, pri­ma­ry sub­sta­tions step in to mit­i­gate the effects. Fluc­tu­a­tions at the low-volt­age lev­el, how­ev­er, often go unno­ticed by util­i­ty providers because there is no mon­i­tor­ing sys­tem in place.

RELIABILITY FOR INDUSTRIAL OPERATIONS

At the same time, elec­tron­ic con­trol sys­tems used in plants and machines are becom­ing more and more sen­si­tive to these fluc­tu­a­tions. The abil­i­ty of indus­tri­al com­pa­nies to run effi­cient­ly and reli­ably is there­fore increas­ing­ly depen­dent on the adher­ence to a defined volt­age range. Any devi­a­tions from this range are guar­an­teed to cause inter­rup­tions in pro­duc­tion process­es. Even if the devi­a­tions last only a frac­tion of a sec­ond, they can cause sen­si­tive fre­quen­cy con­vert­ers in many machines to shut down, requir­ing oper­a­tors to start them up again. If volt­ages stray out­side of the spec­i­fied range for an extend­ed peri­od of time, the dam­age becomes even more severe due to the cor­re­spond­ing­ly lengthy down­time peri­ods, which affect glass and steel works in par­tic­u­lar.

Con­sumers of elec­tric­i­ty from the pow­er grid are usu­al­ly able to con­nect and oper­ate vir­tu­al­ly any num­ber of devices and instal­la­tions to the net­work with­out con­sult­ing the grid oper­a­tor, and at best this means that oper­a­tors can only keep the qual­i­ty of the sup­ply volt­age under con­trol with­in a sta­tis­ti­cal frame­work.

Mod­ern pow­er grids may only present a low risk of equip­ment drop­ping out, but the empha­sis is on the word “low”. The ques­tion is not whether fluc­tu­a­tions will cause inter­rup­tions in the pro­duc­tion process, but rather how seri­ous they will be when they do occur. If these tech­ni­cal­ly unavoid­able resid­ual risks are to be guard­ed against on a case-by-case basis, appro­pri­ate mea­sures must be intro­duced direct­ly where they are need­ed. In this exam­ple, action would need to be tak­en direct­ly in the sup­ply sys­tem for the pro­duc­tion facil­i­ties at the com­pa­ny itself. This means that indus­tri­al com­pa­nies wish­ing to err on the side of cau­tion need to take volt­age qual­i­ty into their own hands.

BUILDING A SECURE INTERNAL GRID

This is exact­ly the action tak­en over the last year by the ger­man com­pa­ny Säch­sisch-Bay­erische Stark­strom-Geräte­bau GmbH (SBG). In 2017, a sit­u­a­tion arose in which the volt­age lev­el plum­met­ed. Frank Tiep­n­er, respon­si­ble for over­see­ing pro­duc­tion engi­neer­ing at SBG—a lead­ing man­u­fac­tur­er of dis­tri­b­u­tion trans­form­ers and spe­cial machines—explains how this prob­lem led to a change in think­ing: “We were able to see that the volt­age was fluc­tu­at­ing with­in the spec­i­fied range from the read­ings we took over the years from the meters in the sub-dis­tri­b­u­tion units.”

Machines were repeat­ed­ly break­ing down and, as he recounts, the rea­son was not easy to iden­ti­fy: “In this spe­cif­ic case we were unable to estab­lish whether the issue was being caused by volt­age fluc­tu­a­tions, a short-cir­cuit in the grid, or anoth­er pow­er con­sumer cre­at­ing a prob­lem in the grid. Nor­mal­ly, we were able to sim­ply start up the machine again and con­tin­ue pro­duc­tion.” How­ev­er, in ear­ly 2017 some­thing else hap­pened.

The ener­gy sup­pli­er had car­ried out con­struc­tion work on the grid, lead­ing to mas­sive volt­age dis­rup­tions. “At one point the volt­age fell below 350 volts,” explains Tiep­n­er, “and we could do lit­tle more than watch as one machine after the oth­er broke down and brought arge sec­tions of the pro­duc­tion line to a stand­still. That def­i­nite­ly served as a wake-up call. In a large com­pa­ny like ours, these inci­dents war­rant a prop­er response. For this rea­son, we explored the pos­si­bil­i­ty of guard­ing against such events by safe­guard­ing our inter­nal grid.”

Tiep­n­er and his col­leagues thus went in search of the most cost-effec­tive solu­tion. It soon became clear that only one solu­tion would fit the bill: The three con­ven­tion­al dis­tri­b­u­tion trans­form­ers, which were con­nect­ed in par­al­lel and sup­plied pow­er to the company’s inter­nal grid, had to be removed. In their place, the job would be car­ried out by three volt­age reg­u­lat­ed dis­tri­b­u­tion trans­form­ers (VRDT) from SBG, fit­ted with ECOTAP® VPD®. “When con­sid­er­ing our exist­ing infra­struc­ture, the SBG VRDT was by far the most cost-effec­tive solu­tion because the ECOTAP® VPD® allows us to install reg­u­lat­ed trans­form­ers with exact­ly the same foot­print as the unreg­u­lat­ed ver­sion. So in that sense it’s almost a plug-and-play solu­tion.

“At one point the volt­age fell below 350 volts, and we could do lit­tle more than watch as one machine after the oth­er broke down.”Frank Tiep­n­er

The instal­la­tion and con­nec­tion con­di­tions are iden­ti­cal, so it couldn’t be eas­i­er. We didn’t have to change any­thing about the main dis­tri­b­u­tion with the ex-pen­sive cir­cuit break­ers, or the bus­bar sys­tem which is designed for sup­ply­ing the three trans­form­ers.”

With the par­al­lel con­nec­tion of VRDTs, SBG had reached hith­er­to unchart­ed ter­ri­to­ry. For such sit­u­a­tions, among oth­er rea­sons, Rein­hausen devel­oped the ECOTAP® VPD® CONTROL PRO con­trol sys­tem (see box). In order to ensure that the tap chang­ers of all three trans­form­ers per­form iden­ti­cal switch­ing oper­a­tions at the exact same time, there­by pre­vent­ing tap dif­fer­ences, the con­trol sys­tem cre­ates a master/slave oper­a­tion. This means that one of the tap chang­ers sends a con­trol com­mand to the oth­er two, thus ensur­ing smooth oper­a­tion. Frank Tiep­n­er was also excit­ed by the oth­er pos­si­bil­i­ties afford­ed by the con­trol unit: “The con­trol sys­tem can be very pre­cise­ly pro­grammed using a web-based inter­face. There is also a wide range of ways in which we can reg­u­late, mon­i­tor, and con­trol the trans­form­ers.” Tiep­n­er believes that the goal of guar­an­tee­ing grid sta­bil­i­ty has now been achieved.

“Par­al­lel-con­nect­ed trans­form­ers are com­mon­place even in indus­tri­al com­pa­nies. How­ev­er, reg­u­lat­ed dis­tri­b­u­tion trans­form­ers con­nect­ed in par­al­lel on the pri­ma­ry and sec­ondary sides are a real nov­el­ty.” Michael Büh­n­ert, head of sales in Ger­many at SBG, goes fur­ther: “Many of our cus­tomers today are already ben­e­fit­ing from the tech­ni­cal exper­tise we have accrued togeth­er with MR, and a grow­ing num­ber of them work in indus­tries where SBG VRDTs are employed along side Rein­hausen con­trol sys­tem tech­nol­o­gy.”

DECIDING ON A VRDT SYSTEM

Cus­tomers of the Tai­wanese trans­former man­u­fac­tur­er Shih­lin Elec­tric & Engi­neer­ing Cor­po­ra­tion are also faced with sim­i­lar prob­lems, but against a dif­fer­ent back­drop. While it is the volatile feed-in of renew­able ener­gies that places a bur­den on the Euro­pean grid, indus­tri­al com­pa­nies in South­east Asia often have to con­tend with weak grids and extreme volt­age fluc­tu­a­tions. Accord­ing to Joseph Kuo, Senior Vice Pres­i­dent at Shih­lin: “The weak­est grids in the South­east Asian mar­ket are found in Myan­mar, Laos, and Cam­bo­dia. In these cas­es, it is cer­tain­ly advis­able to safe­guard pro­duc­tion.” But ulti­mate­ly, Kuo is see­ing huge demand through­out the whole of South­east Asia for tech­nolo­gies designed for indus­tri­al com­pa­nies that want to be pro­tect­ed against the con­se­quences of volt­age fluc­tu­a­tions.

He takes one cus­tomer as an exam­ple. A Tai­wanese com­pa­ny that oper­ates a pro­duc­tion facil­i­ty in rur­al Viet­nam was report­ing extreme insta­bil­i­ties, par­tic­u­lar­ly dur­ing the sum­mer months. Pro­duc­tion was stop­ping for 10 to 15 min­utes sev­er­al times per month due to sig­nif­i­cant volt­age fluc­tu­a­tions.

“Thou­sands of fac­to­ries in South­east Asia are con­tend­ing with volt­age fluc­tu­a­tions. The demand for sta­ble inter­nal com­pa­ny grids is huge.”Joseph Kuo, Shih­lin Elec­tric & Engi­neer­ing Cor­po­ra­tion

The pro­duc­tion down times alone cost the com­pa­ny over 25,000 US dol­lars. In addi­tion, the main switch was also dam­aged. Shih­lin Man­ag­er Kuo explains that “thou­sands of pro­duc­tion com­pa­nies in South­east Asia have to con­tend with exact­ly these types of prob­lems. This gives us an idea of just how high the demand is for tech­nol­o­gy for sta­bi­liz­ing inter­nal com­pa­ny grids.”

Shih­lin is meet­ing this demand with dis­tri­b­u­tion trans­form­ers. To this end, Rein­hausen deliv­ered an ECOTAP® VPD® to Tai­wan in Sep­tem­ber 2017. The end cus­tomer was an indus­tri­al com­pa­ny in Myan­mar that had ordered a reg­u­lat­ed 1.5 MVA trans­former from Shih­lin Elec­tric & Engi­neer­ing Cor­po­ra­tion. Lar­ry Hsieh, Man­ag­er of Mate­r­i­al Pur­chas­ing Cen­ter at Shih­lin, explains why they decid­ed on a tap chang­er from Rein­hausen: “We ini­tial­ly con­tem­plat­ed procur­ing a tap chang­er from a man­u­fac­tur­er in Shang­hai.

Using a local busi­ness with a shared lan­guage seemed very appeal­ing to me at first. As a buy­er, the costs are of course the most impor­tant aspect. The ECOTAP® VPD® is extreme­ly com­pet­i­tive in this regard, as well as being a prod­uct from the world­wide leader in OLTC man­u­fac­tur­ing. This was cru­cial to our deci­sion, along with the strength of the Rein­hausen brand, the reli­a­bil­i­ty and qual­i­ty of the prod­ucts, and the strong ser­vice sup­port.”

A WELL-MAINTAINED GRID

Reg­u­lat­ed trans­form­ers can also sta­bi­lize volt­age in sys­tems where cable lengths and load changes lead to fluc­tu­a­tions, as was the case with RWE Pow­er AG. RWE put two con­trol­lable three-wind­ing trans­form­ers into oper­a­tion in the Ham­bach lig­nite sur­face mine in Ger­many. The mine is locat­ed to the west of Cologne, right in the heart of the lig­nite fields sur­round­ing the riv­er Rhine. It opened in 1978 and cur­rent­ly reach­es a depth of about 400 meters. Safe extrac­tion of coal in the open-pit mine requires engi­neers and work­ers to low­er the water table by drilling wells, installing pumps, and lay­ing pipelines. Drainage is achieved using pump shafts. Elec­tric­i­ty is sup­plied to the shafts by com­pact sta­tions or direct­ly from medi­um volt­age.

A com­pact sta­tion con­tains a dis­tri­b­u­tion trans­former, a medi­um-volt­age sys­tem, and a low-volt­age sys­tem. A fre­quen­cy con­vert­er pow­ers the shaft pump, which has a nom­i­nal out­put of 400 kW. The cables in this 6 kV grid are very long. As a result, fluc­tu­a­tions of elec­tric­i­ty in the grid often occur dur­ing switch­ing oper­a­tions or load changes. This in turn some­times inter­feres with the inter­me­di­ate cir­cuit of the fre­quen­cy con­vert­er. Nev­er­the­less, this is a prob­lem that work­ers at RWE, togeth­er with the Pow­er Qual­i­ty experts from MR, have since man­aged to solve. It became rapid­ly clear that the best tech­no­log­i­cal solu­tion was again the ECOTAP^® VPD^®. Anoth­er huge advan­tage of Rein­hausen from the per­spec­tive of RWE is that it already meets the require­ments of the EU Ecode­sign Direc­tive for 2021.

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YOUR CONTACT

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