INMRINMRSource of Information on International Developments in Transmission & Distribution

Issue 82 • Quarter 4 - 2008 • Volume 16 - Number 4

REPRINTED WITH PERMISSION

German Tap ChangerManufacturer Extends Product

Range to Hollow Core Insulators

INMR® Q4 2008 GERMAN TAP CHANGER MANUFACTURER EXTENDS PRODUCT RANGE...2

German Tap ChangerManufacturer Extends ProductRange to Hollow Core Insulators

German Tap ChangerManufacturer Extends ProductRange to Hollow Core InsulatorsMaschinenfabrik Reinhausen (MR), one of the world’s major suppliers oftap changers and monitoring equipment for transformers, has recentlyentered the fast-growing field of hollow core composite insulators. Themove is not the surprise it might appear at first glance since MR has longbeen a manufacturer of perhaps the most vital component within theseinsulators - namely the FRP tubes which provide their mechanical strength.

INMR visits the new insulator production facility located outsideRegensburg and discusses the factors behind this expansion decision aswell as how MR has organized its manufacturing process.

INSULATORS

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A ccording to Jürgen Hauck, therecent move into the market forhollow core insulators is

consistent with the basic corporatestrategy to supply all types of itemslinked to the transformer. Says Hauck,whose background at MR has been onthe tap changer side, “we seeeverything around the transformer asfitting into our sphere of business,except for the transformer itself, whichwe regard as the business of ourcustomers. Since composite hollowcore insulators are a key componentfor a range of devices such asbushings, this philosophy has madethem a logical product addition.”

To better promote and develop thisproduct area, MR has chosen toestablish a separate Division calledthe Power Composites Business, ofwhich Hauck is Director and whichnow groups together items builtaround FRP tube technology. Theseinclude the FRP tubes themselves,the new line of hollow core insulatorsand specialized wind energyaccessories. According to Hauck, thisDivision has in short time become thefastest growing within the companywith double digit increases in salesvolume every year since 2005.

Manufacturing of the new line ofinsulators takes place in a large plantlocated in Haslbach, about a 10-minute drive from the company’slongtime main facility in the historictown of Regensburg and where all tapchangers are still being produced.The Haslbach plant was built in1993 but, with the rapid expansion

in sales, there are now plans toenlarge it significantly.

Hauck explains that tubemanufacturing at MR began some 25years ago at a time when thisexpertise was hard to find on themarket even though it was one of thekeys to the tap changer business.Indeed, the FRP tube is still regardedas one of the most vital componentsof a tap changer (both on-load andoff-circuit type), which apart from themotor drive can consist of thousandsof separate parts. Having this tubecapability in-house is seen as givingMR Power Composites a strategicadvantage in the insulator market.Says Hauck, “Most other insulatormanufacturers do not produce theirown tubes. But we already have thisknowledge and, given our familiaritywith issues of leakage current as wellas attachment of metal fittings, weknew we could do this businessourselves without relying on anyoutside sources.”

Indeed, Head of Marketing for thecomposite insulators product line,Jens Frost, explains that MR is amongthe only insulator manufacturers whocan also design, machine and test itsown flanges. “This additionalcapability,” he points out, “is fairlyunique in our business area.”

Head of Production, Roland Höfner,whose background is in the insulatorindustry, agrees. “Generally,” henotes, “while most other insulatormanufacturers have to rely on outsidesupport in such areas as mechanicaland electric field calculations, we cando both ourselves. We can also takeCAD drawings from a customer anduse them as the basis for our ownfinite element analysis calculations.”

Taking INMR on a tour of the newinsulator production area, Hauckbegins by noting that some Euros 7million (about US $ 10 million) havebeen invested here just this year and asimilar amount is planned for thecoming year as well. Entering the largearea where FRP tubes are produced bythe filament winding process commonto this industry, one of the first thingsFrost points out is that the Division’s

Having the FRP tubecapability in-house isseen as giving MR’sPower Composites

business unit a greatstrategic advantage inthe insulator market.

Inspection of tap changer before finalassembly. Tube in background is ofsame type as used in hollow corecomposite insulators.

FRP tubes such as these are seen as astrategic component in producing hollowcore composite insulators.

Ensuring perfectly smooth inner surfacesin FRP tubes required polished mandrelsfree of any surface blemishes.

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name of Power Composites wasselected because all the tubesproduced in this facility are designedto possess an energy withstandcapability. This he says differs frommost other tube suppliers who have tooffer two separate production lines fortubes – one for HV electricalapplications and the second forunrelated end uses.

Winding of the tubes is done onpolished steel mandrels whose chromesurfaces must be completely free of anydefects or scratches so as to ensure aperfectly smooth inner surface for thetube. At the moment, the MR facilityhas two large winding machines, one ofwhich is new while the older model isscheduled for a retrofit to incorporatethe latest winding technology. Höfnerindicates that additional new windingmachines are now on order and to bedelivered in the coming months. These,he says, will further improve productionby permitting very small winding anglesresulting in tubes with even betterbending resistance. At the moment,most existing machinery in this industryis limited to a minimum winding angleof about 20°. Höfner also notes that anew milling machine is on order andwill be able to accommodate tubes ofup to 11 meters.

Production of single tubes of such alength is not practical and, as iscommonly done for very long hollow

porcelains, whenever tubes of thisdimension are required, they areproduced by gluing together twoseparate units. Höfner emphasizes thatthe strength of the resulting bond is sogood that if bending tests areperformed to destruction, the breakwill almost always occur at another

point along the tube and not at theglued joint.

Among the keys to a well-producedFRP tube are the rovings as well asthe epoxy resin system into which theyare dipped for impregnation justbefore winding onto the mandrel.Sales Manager, Georg Schütz, explainsthat the basic raw material for a tubeis the glass fiber filament that issupplied on spools already wound intolarger cross-sections called rovings.Their unit of measurement, based onweight, is referred to as ‘tex’. Typically,smaller rovings are combined andcomprise one larger one with differentpossible tex weights. Says Schütz, “tomanufacture a good tube, it’s criticalto combine a high glass content withthe correct computer-controlledwinding program.” This, he adds, isbecause the final mechanical strengthof the tube for any torsional or bendingloads is determined entirely by its wallthickness as well as by the angle ofwinding of the impregnated rovings.“Being able to offer variable wallthicknesses for most mold diameters,”

Steel mandrels have special smooth chrome surfaces. Curing oven in backgroundprovides continuous heating to optimize curing cycle.

Glass fiber rovings from spools are impregnated in an epoxy resin bath just before computer-controlled winding onto mandrel.

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he says, “enables us to tailor-make ourinsulators according to our customers’precise requirements.”

Höfner says that MR employs twotypes of electrical grade resin systemsfor dipping the rovings just before theyare wound onto the mandrel: astandard resin with a glass transitiontemperature (tg) of 128° C, which heclaims is very good by most industrystandards; and another which retainsits mechanical strength up to 156° C.The latter tubes usually findapplication in tap changers.

Another investment planned for thecoming year is an automated systemfor preparing and delivering this resin,which consists of six componentsincluding the epoxy, a hardener andvarious accelerators. Automation isseen as key to increasing processefficiency and also the consistency ofthe resin mixture from one batch tothe next. Another goal, according toHöfner, is reducing any risk of bubblesfrom manual mixing.

MR’s manufacturing process sees thetube put through a continuous heatingcycle designed to make the curingprocess more efficient and increasethe productivity of each machine. Withthis system, each machine canapparently produce more than 20tubes per day.

After curing, each finished tube isremoved from the mandrel andproceeds to the next step, whichinvolves cutting the ends and turning.Now, the tube is ready for attachmentof the flanges – a highly guardedprocess that must be done in a roomfree of any dust or outsidecontaminants and where a great dealof know-how is apparently involved.Höfner states that attachment of theflange to the tube is based on

ultrasonic cleaning of each partfollowed by a combination of gluingwith an epoxy resin glue having a tgsimilar to the epoxy resin, andshrinking.

Frost points out that the PowerComposites plant has been dividedinto two main areas – one section thatprocesses all the metal parts such asflanges and the other for all kind ofinsulation material including hollow-insulators. “We never mix metalworking and composite manufacture inthe same hall,” he emphasizes.“That’s another reason we use only E-glass and none with carbon fiberswhich would pose a hazard throughtheir conductive dust.” Another of theconcerns in this production area is tokeep all flying insects out.

Frost goes on to emphasize howimportant it is that every manufacturerof tubes for insulators should have anin-depth knowledge of their ultimateapplications. Otherwise, he states,there may be sources of partialdischarge activity and the tubes willnot survive under the high electricalstresses encountered during service. Infact, he points out that it is for thisreason that every tenth tubemanufactured at the facility is testedfor puncture in both axial andcircumferential directions. Also slab orring samples taken from tubes areexposed to a minimum of 75 kV forone minute and usually no punctureoccurs, even up to 145 kV.

The MR factory is equipped with aspecial in-process quality control areawhere, apart from puncture testing, anumber of other required tests areperformed on sample tubes, includingmechanical as well as leakage testsunder helium. Every tube is thenassigned a unique bar code, whichidentifies all its relevant production

Winding angle of resin impregnatedrovings is one of the keys to mechanicalstrength of resulting tube.

After attachment of flanges, tubes areready for priming and molding.

In-process mechanical testing of tube.Special acoustic meters can detect anymechanical damage.

“Since we started in this businesscomparatively recently, we took into ourmachinery and process design the latestknowledge and industry experience.”

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parameters and which stays with thetube all the way through the remainingproduction steps. Höfner says that sucha tracing system allows each tube tohave its complete production historyavailable at a glance.

After attachment of the flanges andcompletion of all required tests, thefinal major step in the productionprocess involves casting a silicone shedonto the tube. Before entering themolding machine, however, the tube issprayed with a thin layer of chemicalprimer intended to ensure a perfectbond between the silicone rubber andthe FRP tube.

Molding equipment can be quite costlyand for this reason typically representsthe bottleneck for any factorymanufacturing insulators or similarcomponents such as arresters. It is forthis reason that every supplier tries tooptimize the molding cycle with thegoal to shorten it as much as possible.Frost sees the fact that MR is a recententrant into this business as a majoradvantage. “Since we started onlyrecently,” he explains, “we built intothe design of our machinery andprocess the latest knowledge andindustry experience.” Among thecustomized machine features he refersto are high-speed filling and reducedvulcanization time for the rubber.

The silicone material itself is a standard,low viscosity LSR formulation producedby one of the large chemical companiesin Germany. It is delivered as a two-component system pumped into a staticmixer and from there dosed directly intothe mold cavities. Höfner points out thatMR has developed its own molding tool,flexible enough to accommodatealternating sheds and different insulatorlengths without having to alter theprofile. He also points out that toolingtechnology is much more complex thanmight appear at first glance since it alsoincludes specialized surface treatmentsdesigned to reduce both the moldingcycle and the pressure needed toremove the insulator from the mold aftervulcanization.

The shed design selected is not ahorizontal angle profile but rather tiltedon its lower side, as is often seen with

Bar code placed on tube identifies all itsrelevant production parameters.

Shed design of typical insulator alreadypackaged by MR Power Composites.

Oven for post-curing after removal ofinsulator from the mold.

Removal of mold line is final step beforepackaging.

Customized clamping machine for casting silicone sheds onto primed FRP tube.

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porcelain. This, claims Höfner, yieldslarger shed diameters and allows thespacing between sheds to be wider forthe same creepage so as to minimizerisk of ice bridging or flashover. “Ourspecial profile design,” adds Frost,“gives better protection for the lowerportion of the shed during rain, evenwhen it does not fall vertically.”

After removal from the mold, thefinished insulator is placed into anearby heating chamber for anadditional curing cycle of up to fourhours – a step not usually seen in thisindustry. Höfner recognizes this butinsists that this additional curingensures that the silicone material willthen offer its maximum resistance todeformation under any loads.After this final curing, the insulatorundergoes a brief treatment to removeany evidence of the mold line andafterwards is ready for final packaging.But first each unit enters a finalquality control station that assemblesall the production data for every singlepiece produced. A special code isengraved on the flange providing boththe product serial number and thecustomer part number for easyidentification.

An additional quality control facilitynearby performs regular testing oneach batch of silicone that arrives atthe plant in order to allow adjustingthe molding cycle requirements to anyslight change from one batch to thenext. A special testing device is alsoavailable to check the bonding of thesilicone to the FRP tube material andexamine the interface between epoxyand silicone. This is being done foreach batch of every type of insulatorproduced.

Hauck and Frost are optimistic aboutthe future of MR’s new insulatorbusiness and claim that there is nowclear evidence of a growing level of

substitution for porcelain, meaningthat this segment will grow rapidly. Infact, even though the first insulatorsequipped with silicone sheds were notproduced at the facility until early2007, MR already has nearly two-dozen customers from all over theworld. Nor is being located in acountry with comparatively high laborcosts seen as posing any competitivedisadvantage in the increasingly globalinsulator industry. Says Sales ManagerSchütz, “for these types of products,from 60 to 80 percent of the final costof the insulator is material driven andthe bigger the insulator, the greater thecost component contributed bymaterials. Therefore, whatdifferentiates the competition is not somuch price but quality, lead time andreliability of delivery. This is what thecustomer is focused on.”

In regard to delivery, Hauck sees this asone of the keys to future marketsuccess. Recognizing that the relativelylong production lead time of porcelain isone of its strategic weaknesses, he saysthat MR can typically supply a finishedinsulator to its customers in less than amonth and, in special cases, sometimeseven less – a lead time that he claimscan rarely be matched by porcelain orother competitors. “We have new tubescoming through the factory every threedays based on incoming orders,” hesays, “and this means that, unlike otherinsulator suppliers, we can move veryquickly to the next stages ofproduction.”

Adds Schütz, “the key to success inour business is having a very highvertical integration, meaning thecapability to produce both tubes andflanges. In our case, having both in-house means that we can take fullcontrol over the entire manufacturingprocess while competitors must rely onoutside suppliers to ensure gooddelivery times.”⌧

“For these types of products, from 60 to80 percent of the final cost of the

insulator is material driven – the biggerthe insulator, the greater is this costcomponent contributed by materials.”

Testing for bonding strength of LSR toepoxy resin substrate.

Final quality control station uses photosof possible damage as guide to finalinspection.

Production number and customer partidentification are engraved onto flange.

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