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Taming theArc

Carey Cook, John Opfer, and Kristin McIinnis, Guest Authors

This article celebrates the100th anniversary ofS&C Electric Co. andthe company’s numer-ous accomplishments.

Electric AgeAt the dawn of the electric age, theindustry had to make a choice: ThomasEdison’s low-voltage, direct-currentdistribution networks or George West-inghouse’s high-voltage, alternating-current grid. The former required thick,expensive copper conductors to mini-mize power losses. The latter’s use ofthin wires won out and is still in usetoday. However, it came with its ownchallenges because high-voltage circuitscould cause arcing, explosions, and fires.

One such fire took place in 1909 atCommonwealth Edison’s (ComEd) FiskGenerating Station in Chicago, thenone of the country’s largest generationfacilities. The fire, caused by a primitivefuse, prompted two of ComEd’s engi-neers to begin working on their ownand to devise better ways to interrupthigh-voltage current.

EdmundO. Schweitzer and Nicho-las J. Conrad became prolific inventorsof circuit-interruption technologies.Their first breakthrough was a ‘‘liquidfuse” that confined the high-voltagearc inside a glass tube (Figure 1). Theyfounded Schweitzer and Conrad, Inc.(S&C) in 1911 to sell that product.Over the next 100 years, the companydeveloped many elegant solutions tothe brute-force necessities of high-voltage circuit interruption. Competing

at first against small suppliers andthen corporate giants including Gen-eral Electric and Westinghouse, S&Ccarved out a niche as a ‘‘specialist inhigh-voltage switching and protection.”The Chicago-based company has earnednearly 1,000 patents and today is aleader in electronic switching andprotection technologies that wouldastound the company’s founders.

The High-Voltage ChallengeLike water in a fire hose, the pressureof a high-voltage circuit causes currentto jump across a gap. The white-hotarc resists efforts to be extinguished.

Without adequate air spacing and insu-lation, or innovations such as vacuuminterruption and insulating gas, thehigh-voltage current will flash over toground or from one phase to another.The arc will also travel along any suffi-ciently conductive path, including ion-ized air or a carbon trace, to completethe circuit, often with disastrous results.

The higher the voltage or current,the more powerful the arc. A fuse thatblows on a 14.4-kV distribution lineechoes like a dynamite blast. An arcin a 138-kV transmission substationis even more dangerous and difficultto extinguish.

So, in the early 20th century, as util-ities built higher-voltage grids to servehomes, factories, and office buildings,there were huge opportunities for entre-preneurs who could provide the equip-ment that would keep the networks inoperation. S&C had something no oneelse did, the liquid fuse. Protected bypatents and updated continuously, thefusewas, likemany good inventions, sim-ple in concept but complex in the details.

There are three basic rules of break-ing a high-voltage arc: elongate it, coolit, and strip it of free-moving ions. Theliquid fuse did all three. Inside the tubewas a spring-loaded fusible elementthatmeltedwhen a short-circuit currentheated it. The spring rapidly pulledapart the two ends of the melted ele-ment, while the liquid inside the tube,carbon tetrachloride, cooled and deion-ized the arc. The tricky part was theglass tube, which had to withstand sub-freezing winter temperatures and then,in less than a second, a 5,000-K arc.S&C took their problem to a specialty-glass company named Corning. The

Digital Object Identifier 10.1109/MIAS.2011.941715

Date of publication: 15 August 2011

1077-2618/11/$26.00©2011 IEEE

1S&C was founded in 1911, and its firstproduct was the liquid power fuse.(Photo courtesy of S&C.)8

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resulting borosilicate glass later ap-peared in kitchens across Americaunder the Pyrex trademark.

Flipping the SwitchThe liquid fuse was followed in 1922by a bayonet-style ‘‘ejector cutout”with a spring-loaded link that wasejected from the tube to ensure aquick, positive break. Then came asolid-material fuse with a lining ofcompressed boric acid powder thatvaporized on contact with the arc toproduce cooling, deionizing gases. Asutility loads and system voltagesincreased, S&C’s engineers beefed upthe tubes and lengthened the fuses toincrease the distance an arc would haveto travel to complete the circuit.

These bread-and-butter productskept S&C’s factory busy. However,they solved only one of the problemsfaced by utilities: interrupting shortcircuits. The other problemwas switch-ing a live load.

High-voltage electricity is typi-cally transmitted on a three-phasebasis using the system developed byNicolas Tesla in the late 1880s. Switch-ing open an energized circuit (thefamiliar three-conductor grouping seenon power poles) usually requires threeswitches that operate simultaneously.The switches must be far enough apartto prevent current from jumping fromone phase to another. And they mustbe precisely engineered and manufac-tured to assure reliable, fast performance.

The first effective load switches wereoil-filled circuit breakers that quenchedand cooled the arc inside tanks ofnonconductive oil. The same basictechnology is still used today. How-ever, early circuit breakers were expen-sive, heavy, and prone to overheating.

Nicholas Conrad sketched out analternative device at his kitchen table.His pantograph switch provided veryrapid blade motion as the circuit wasbroken (Figure 2). It featured springyconductive contacts known as buggywhips that further elongated the arc asthey pulled away from the opposingcontacts. This ‘‘air-break” switch wasnot a perfect solution, though, becausethe arc could jump phase to phase in astrong crosswind. But it earned Con-rad another patent and was deployedby the hundreds in utility substations.

No External ArcNicholas Conrad sold his interest inS&C in 1930 because of poor health.However, the engineering staff contin-ued on under motor-control manufac-turer Cutler-Hammer, registering 111more patents during the Depression.(Conrad and his son, John, would buythe company back afterWorldWar II.)One of their most important inven-tions was the load-break interrupter,devised by Sigurd Lindell and AnthonyVan Ryan (Figure 3). Like the liquidfuse, it confined the arc inside a sturdychamber, this time made of brass. Asits spring-loaded contacts opened, arcplasma vaporized a deionizing lining,snuffing the arc.

It was an ‘‘ablative” interrupter. Asthe arc eroded the top layer of the

3The load-interrupter switch promised‘‘no external arc” operation (circa 1940).(Photo courtesy of S&C.)

2The pantograph switch used rapid blade action to interrupt the circuit (circa 1925).(Photo courtesy of S&C.)

4(a) (b)

(a) The Loadbuster (circa 1958). (b) An S&C sales engineer demonstrates theLoadbuster Tool at a 1971 trade show in Porto Alegre, Brazil. The inset shows thearc that forms if a circuit is opened with a conventional hook stick. (Photocourtesy of S&C.)10

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acrylic liner, the resulting gas attractedions from the arc plasma and extin-guished it. Unlike a solid-materialfuse, whose lining is used up in a singleinterruption, the load-break inter-rupter could handle multiple opera-tions. Utilities could now routinelyopen energized circuits for mainte-nance or to reconfigure groups ofswitches to restore power after outages.

During World War II, materialshortages made oil-filled circuit break-ers difficult to procure. S&C’s engi-neers responded by developing fuse-and-switch combinations mountedinside wooden cabinets. By interrupt-ing with no external arcs, fire was nota concern. This product subsequentlyevolved into metal-enclosed switch-gear and, later, pad-mounted gear; thesetwo products are still in wide use today.The latter features group-operatedthree-phase switches with fiberglassinsulating barriers between the phases.Many of the forest-green boxes seen insuburban office parks are S&C Pad-Mounted Gear.

Another application of the ablativeinterrupter was S&C’s Loadbuster tool,first offered in 1958. This lightweight,portable interrupting device is mountedon the end of a lineman’s hook stick.When attached to a cutout or discon-nect, the tool routes current throughthe interrupter before breaking theload. Because the Loadbuster allowsutilities to open an energized circuitwithout the need for a load-interrupterswitch, it remains a workhorse tool forline crews around the world (Figure 4).

Beyond Brute ForceCircuit interruption has always beenmore than an electrical challenge. Itrequires chemical engineering todevelop arc-extinguishing agents andhigh-performance insulation, includingthe cycloaliphatic resin that S&C devel-oped and trademarked as Cypoxy.Expertise is also needed in metallurgyand electroplating to prevent corrosionat arcing points and on current-carryingcomponents. Mechanical precision isparamount not only in design but alsoin fabrication and assembly becauseswitching mechanisms must be fast,accurate, and durable over the life of theequipment, often 30 years or more.

Rigorous testing is essential. In theearly years, S&C performed mechani-cal and chemical tests in its own labo-ratory and in the alley behind the

factory, where engineers proved theice-breaking capabilities of switchesby spraying them with water duringChicago’s winters. For high-voltagetesting, S&C worked with utilities intheir substations. In the 1950s, S&Coutfitted a test instrumentation vanwith oscilloscopes, sensors, and high-

speed cameras to observe and record thevoltage spikes and other ‘‘transients”caused by switching, short circuits,and other events (Figure 5).

S&C engineers regularly traveledwith their prototypes to the high-power KEMA laboratories at Arnhemin The Netherlands, an expensive but

5A test instrumentation van performing tests on a live circuit (circa 1958). (Photocourtesy of S&C.)

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a necessary step in product R&D. Toreduce such trips, in 1961, S&C builtits own high-power laboratory. Anarcing chamber allowed techniciansto test ablative materials and insula-tors. A high-voltage test cell simu-lated lightning surges. And a short-circuit generator tested componentsat high-fault currents. Inside the lab-oratory’s explosion-proof doors, thou-sands of S&C devices were sacrificedto test their limits and develop morerobust designs. In 2010, S&C openeda new laboratory called the AdvancedTechnology Center that had 17 timesthe power of the previous facility.

Transmission and distribution gridsspread rapidly in the second half of the20th century to serve America’s boom-ing suburbs. S&C stuck to its niche,building a reputation for innovativeengineering and long-term value,though not always at the lowest price.Company president and primary ownerJohn Conrad heavily reinvested profitsto develop new technologies. He

resisted diversification into devicessuch as circuit breakers and reclosersand avoided commodity-type products.The only sure survival technique, Con-rad would say, was to ‘‘have the kind ofproduct that no one else makes.”

Insulators, Puffers,and Vacuum BottlesThe S&C Circuit-Switcher, introducedin 1959, was a transmission-class switchthat could replace circuit breakers incertain applications at considerablesavings (Figure 6). It offered a whollynew approach to transformer protec-tion, using multiple gaps, nozzles, and‘‘puffers” to stretch and cool the arcinside sealed, air-filled interrupters.The first version used ablative inter-ruption technology, but it was soonupgraded to use sulfur hexafluoridegas (SF6), permitting much higherinterrupting ratings. The interrupterswere controlled by intricate mechanical‘‘brains,” another milestone in S&C’sdevelopment of high-speed mecha-nisms to effect circuit interruption.

S&C’s engineering teams took onnew challenges in the 1970s. Elec-tronic switch controls were developedto quickly transfer load from one sourceto another if a problem occurs. TheFault Fiter electronic power fuse usedelectronics to sense fault current anddivert it into a perforated copper ribbonembedded in sand. As the ribbon arcedat the perforation points, the sandmelted and absorbed the arc’s energy.Fault Fiter provided higher ratings anda better coordination between devicesthan traditional fuses (Figure 7).

Next came a series of products thatcombined electronics, gas insulation,and polymers. In 1990, the Scada-Mate Switching System providedvoltage and current sensing in its

molded Cypoxy pole units, allowingfor a rapid response to outages. VistaUnderground Distribution Switchgear,introduced in 1997, used SF6 insulationto achieve closer phase-to-phase distan-ces than possible with air-insulatedgear. Vista Switchgear was the firstS&C product to incorporate vacuuminterrupters. It also incorporated current-carrying paint on its polymer bushingsto support sensing functions.

Tracking the WaveformBreaking an arc is easiest when thealternating-current waveform crossesthe ‘‘zero point,” when current drops tozero. However, the arc tends to reigniteimmediately after the zero point until itis sufficiently elongated or there are notenough free ions to carry the current.Faster mechanisms, ablative agents, gasinsulation, and vacuum interrupters allreduce the time needed to extinguishan arc. However, none of those technol-ogies can respond as quickly as elec-tronic controls and switches.

Since the 1990s, S&C has used sen-sors and sophisticated power electron-ics to closely track the rise and fall ofthe waveform and respond to distur-bances within a few cycles. The Pure-Wave UPS System can detect avoltage sag or surge and switch to bat-tery power within one-fourth of acycle, about 4 ms. Switching is doneat the zero point using stacks of thyris-tors. There is no arc. A similar fastaction is built into the IntelliRupterPulseCloser (Figure 8), allowing forrapid reconfiguration of circuits afteran outage. Unlike the conventionalrecloser it replaces, the IntelliRupteruses on-board intelligence to provide agentle ‘‘pulse” to test the circuit beforeclosing to restore service. Connectedto other devices via software and high-speed radios, IntelliRupters can create‘‘self-healing” circuits that reconfigurearound a fault, restoring power in sec-onds instead of hours.

When S&C celebrated its 50-yearanniversary in 1961, a company publi-cation predicted that its engineeringteams would push interruption tech-nologies ‘‘beyond today’s comprehen-sion, so that tomorrow’s switching andprotection duties can be performedwith sophistication rather than withbrute force.” The prediction surely hadbeen proven true by the company’s100th anniversary in 2011. The futureis beyond today’s comprehension. IAS

6An early model of the transmission-voltage class Circuit-Switcher (circa1960). (Photo courtesy of S&C.)

7The Fault Fiter electronic power fusefeatured an electronic control moduleand an interrupting module (circa 1982).(Photo courtesy of S&C.)

8The IntelliRupter PulseCloser,introduced in 2009, uses onboardelectronics and high-speed radiosto restore power in seconds. (Photocourtesy of S&C.)12

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