Articulo RIP Bujes

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Source of Information on International Developments in Transmission & Distribution

Issue 68 • Quarter Two - 2005 • Vol ume 13 - Numb er 2

Quarterly ReviewINMRINMRQuarterly Review I N S U L A T O

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Swedish Bushings PlantSees Growth in RIP Designs

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Johansson. Continued efforts to be placed in process optimization.

Jonsson. RIP manufacturing technology more demanding than for OIP.

Winding machine for OIP bushing condensers up to 550 kV.

Computer-controlled machine winds condensers for large RIP bushings.

The nearly 100 year history ofbushings production at ABB andespecially at its flagship Ludvikaplant has provided managementwith an interesting perspectiveon how the changing requirementsof electrical networks has pushedthe advancement of this technology.Bushings Vice President RutgerJohansson and Senior SpecialistLars Jonsson look back at someof the major steps in the evolutionof the bushing since the earliestdays of this plant’s operations.

The very first ABB bushing designswere based on an insulationsystem involving Bakelite material.This type of insulation system,while effective at lower transmissionvoltages, apparently could notaccommodate the move towardhigher voltages without anunacceptable increase in thelevel of internal partial dischargeactivity.

Therefore, as the Swedish powernetwork developed and moved

to 350 kV during the 1940s,the old Bakelite technology hadto be abandoned and replacedwith OIP dielectric systems,which at the time were regardedas quite novel. Says Jonsson,“with the OIP design, we foundthat we could now handle eventhe highest voltage class.For example, by the early 1960s,ABB was able to supply thefirst 750 kV bushings for thenew EHV system of HydroQuébec in Canada.”

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Like the insulator, the bushing isanother of those critical componentswhich comprise all electrical networksand whose failure can have veryerious economic consequences.

Although many in the electric utilityndustry still regard it as nothing

more than a hollow piece of porcelain

with a conductor running through it,notwithstanding its simple appearance,he task performed by a bushing is

actually quite extraordinary.

This is because, for apparatusoperating at many thousands orven hundreds of thousands of volts,t is almost a Herculean task to

adequately isolate the current carrierrom the equipment’s metallic housing.

HV bushings accomplish this task byelying on sophisticated insulationystems able for example to keep

a 550 kV conductor operatingafely only some 20 cm from the

grounded flange.

The basic design of most condenserbushings has not changed in decadesand this is perhaps a tribute to howffective the current technology

actually is. This design involvespecial paper wrapped around theonductor as well as metallic foils

placed at strategic locations withinhis wrap. The precise location

and the size of these floating metalliclectrodes is very important sinceheir capacitive effect controls thelectric field along the unit’s length

and radius.

To achieve its required high dielectrictrength, no air or gas bubbles can

be trapped between the successiveayers of paper. Therefore, theylinder of wound paper and foils thoroughly impregnated with either

oil or a special resin material.Hence the two major technologies

for HV condenser bushings: OIP(oil-impregnated paper and RIP(resin-impregnated paper).

In this article, INMR ContributingEditor Dr. Claude de Tourreil toursthe Swedish plant of ABB - by far

the world’s largest supplier ofbushings. Although the Ludvikafacility still devotes most of itsproduction capacity to the OIP style,developments over the past decadeare apparently now fueling salesgrowth of RIP designs.

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Swedish Bushings PlantSees Growth in RIP Designs

145 kV RIP bushings. P h o t o :

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Although the majority of the bushings made in Ludvikaare still based on OIP technology, the number of RIP unitsproduced annually is apparently increasing steadily.

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Petrici. Recent large investments made in Ludvika plant.

The wrapped condenser paperis then dried to ensure it iscompletely free of moisture beforebeing impregnated with oil orresin. Impregnation, notes Petrici,is quite a delicate operation andthis is much more the case forresin than for oil.

For higher voltage RIP bushingsup to a maximum of 550 kV, resinimpregnation is performed in vesselsof varying size. It is critical that noair bubbles remain in the bulk ofthe insulation after curing becausethese could become the site ofinternal partial discharges whichwould eventually lead to productionrejects.

After impregnation, the mounting

flange and the insulator housing arefitted onto the resin-impregnatedcondenser. In the case of condensersystems for RIP bushings up to170 kV, the external siliconehousing is generally moldeddirectly on to the entire unit.

For OIP bushings, which ABB offersup to 800 kV as part of its standardproduct range, impregnation with oilis carried out in a special computer-controlled installation after thecondenser has been placed insidethe insulator and flange assembly.

Each bushing is first put undervacuum during which time a leaktest is performed. Subsequently,oil is introduced into the bushingto completely impregnate theinternal condenser. Together, thesetwo operations take approximately24 hours.

Both RIP and OIP bushings thenpass through a series of routine testsbefore being cleared for shipment.Capacitance and dielectric lossesare measured up to the powerfrequency withstand voltage whichis maintained for a duration ofone minute.

The magnitude of any dielectriclosses is directly related to themoisture content of the oil-impregnated paper dielectric system(see Figure 1). Detection of partialdischarges is carried out during thisentire test. Some of this testing

requires fairly sophisticated set-upsbecause part or all of the bushing

has to be submerged in oil andbecause there are very tightacceptance criteria on partialdischarges.

Preparation for shipment is thenthe last step of the manufacturingprocess. Shipping bushings in thelower voltage range does not usuallyrequire any special precautionsin the way of packaging. However,large bushings, especially of theOIP type, require sturdy crateswhich can sometimes measuremore than 10 meters in length.

Petrici and Jonsson indicate that,in order to remain a market leader,ABB has invested much in theLudvika production facility in orderto bring it to a level which theyregard as state-of-the-art. At thesame time, they have tried tooptimize all processes for both OIPand RIP designs. Indeed, Johanssonsees that future efforts will likelycontinue to be placed on processoptimization rather than ondeveloping radically new designs.

Another area which Jonsson says hasreceived much attention in recentyears is technical support. With theoptimization (read downsizing) ofengineering staff at many electricutilities, which represent the endmarket for HV bushings, he statesthat technical support offered bymanufacturers has become moreimportant than ever before.

Johansson indicates that ABB ownsbushing manufacturing units located

all around the world, includingRussia, Brazil, South Africa, Indiaand China. The main productioncenters, however are in Sweden,Switzerland and the United Statesand this is where engineeringspecialists are employed to furtherdevelop and improve the technology.

As for the impact of growingcompetition, especially coming fromlow cost suppliers based in Asia,Johansson feels that this does notrepresent a serious threat. The laborcost component in the manufactureof HV bushings, he claims, is justnot a large part of the total cost ofthe product and what really counts,he says, are modern facilities andwell-trained personnel. ⌧

RIP bushings prepared for shipment. P h o

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With the downsizing of engineering staff at electric utilities,technical support offered by bushing manufacturershas become more important than ever before.

n addition, RIP bushings haveow dielectric losses and, like OIP

designs, are partial discharge free.Moreover, they can be installedat any angle and can be energizedmmediately after installation.

Finally, having no oil, they requireess maintenance.

Apart from the increase in marketnterest in RIP bushing technology

due to these advantages, therehas been another design elementhange which is now increasinglympacting the bushings industry.

This involves the substitution ofraditional porcelain housings with

hollow core composite insulators.

Bushings, especially of the RIP type,when equipped with compositensulators having silicone sheds

are increasingly regarded as anxcellent choice when safety and

pollution performance are keydecision criteria.

For example, in case of explosionor vandalism, there is no risk of

fire and the silicone shedsensure superior performanceunder polluted serviceconditions. Yet anotherconsideration promotingincreased market interest,say Jonsson and Johansson,is the superior performanceof these bushings underseismic conditions.

“Given these manyadvantages,” remarks ProjectManager, Roger Hedlund,“the difference between thecost of a porcelain insulatorand that of a compositeinsulator with siliconesheds should not reallybe the decisive factor inthe selection of one typeover the other.”

At the Ludvika bushingsplant, both OIP and RIP bushingsare manufactured in the samelarge hall but on separateproduction lines.

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According to Production Manager,Fredrik Petrici, the characteristicsof all incoming materials are routinelyverified to ensure that they meetvery tight specifications. This isapparently especially importantsince the insulation systems beingproduced are subjected to very highelectrical stresses yet have to deliverproblem-free service for severaldecades. Cleanliness is also stressed,so much so that certain vitalproduction processes are performedonly in enclosed areas.

Specialized computer-controlledwinding machines of different sizeswrap the grade of paper, whichvaries by specific type of condenser,as well as the metallic foils onto acentral tube or solid mandrel rod.A comparatively small unit is usedfor RIP bushings up to 170 kV, whilea very large winding machine canproduce 12 meter long condensersfor OIP bushings having this length.

OIP oil-to-air transformer bushings near test bay.Two 420 units standing vertically in front of fo ur 550 kV units.

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moist: 4% moist: 0.1-0.3%m ois t: 1 % m ois t: 0 .4 -0 .5%

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Is your electrical network reliable?

Read more about bushings underwww.abb.com/electricalcomponents

©2005 ABB

Dry/RIP Bushings from ABBElectrical networks are aging and nearing their capacity while environmentaldisasters are becoming more frequent and severe. Therefore, one must rely ona supplier with the experience and knowledge to deliver innovative solutionsmeeting today’s demanding requirements while lowering life cycle cost.

ABB Bushings have been designed and built considering this. We have over 100 years of experience delivering bushings for transformer, switchgear andother electrical apparatus application. Our dry resin impregnated paper (RIP)bushings provide reliable oil-free service for the most demanding applications.

When combined with a silicone rubber insulator instead of porcelain, one has a self-cleaning, non-brittle,low mass and high mechanical strength design providing increased network reliability during severe

weather conditions, contamination and earthquakes.

Dry or oil-filled, ABB has the right bushing solution for your application. This includes custom solutions for replacement of ABB or other brand bushings at existing installations.

Articulo RIP Bujes

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