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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