Over the past 50 years, new materials have inspired innovation and improved existing technologies.
Inventions and innovations have benchmarked the progress of our society during the last millennium. Many notable discoveries and inventions such as the printing press, the steam engine, the airplane, nuclear fission, electricity and the telegraph have created some of today's most vital industries. However, when survey respondents were asked to identify the millennium's most dynamic force to transform humanity, electricity topped the list.
In some way or form, we rely on electricity for almost everything we do. Electrical advancement drives most technological advancement; therefore, it is no wonder that the demand for electricity has grown at such a rapid rate over the last 50 years. How has the industry kept pace with the late 20th century's unquenchable appetite for electricity? What innovations have impacted the electric industry during this time of heavy growth? Though the basic equipment - circuit breakers, transformers, surge arresters and capacitors - was invented many decades ago, the industry has never become static. New materials drove innovations, which in turn improved existing technologies. Engineers took advantage of this research and of material improvements to bring sweeping change to the last half of the 20th century.
The Ages When historians catalog eras, they tend to group periods of time by the materials that shaped that society. Cases in point: the Stone Age, Copper Age, Bronze Age and Iron Age. So if electricity has shaped our society, then it stands to reason that the past 170-plus years should be called the "Electrical Age." Further, the Electrical Age may be segmented into the "Polymer Age" and the "Silicon Age." It is hard to think of products today that do not contain some form of polymer or silicon.
The Polymer Age Polymer chemistry, which deals with plastics and epoxies, has become a major force to revolutionize the way we live and work. We use Teflon in circuit breaker interrupters. We have developed polymer bushings for breakers and transformers to use in place of porcelain. High-impact polymers have replaced hard rubber for battery cases. Polyvinyl chloride conduit comes in 1000-ft (305-m) rolls, replacing galvanized iron in 10- or 20-ft (3- or 6-m) sections. Neoprene has replaced rubber insulation for electrical cable. Polymer solid dielectric insulation has replaced oil-saturated paper insulation for underground cable. Polymers cure compounds for concrete. Epoxy resins encase air-core reactors, replacing concrete. The list goes on and on. To get an idea of the magnitude of the polymer revolution, we can look at a few specific developments. The following plastic/resin applications - film capacitors, polymer insulators and underground distribution systems - reduced installation, operations and maintenance costs; improved performance; and changed things for the better.
Film Capacitors Polymer film completely changed the anatomy of the power capacitor, which is nearly 90 years old. The first power capacitor application took place in 1914. It had a linen, paper and oil design. This design improved with the replacement of the linen with Kraft paper around 1930. A few years later, askarel (PCB) replaced oil as a dielectric. This design dominated the marketplace through the 1970s. The paper design was expensive, had a limited kilovar unit rating and produced high losses. In 1963, GE Co. invented a process that used polymer, marking the beginning of the end for Kraft paper. The polymer combined a biaxially oriented polypropylene film with Kraft paper. By 1970, GE began field trials on an all-film design. Nine years later, the company replaced the paper design with the all-film version, which has become the standard today. The polypropylene design greatly reduced unit losses and the cost of capacitors. The typical late-1930s paper capacitor design cost a utility about US$10 per kilovar, whereas the all-film price tag read approximately US$1 per kilovar. All-film also increased electrical ratings (600 kVAR vs. 15 kVAR for paper), which has made today's large substation banks practical and economical.
Polymer Insulators Polymer/fiberglass suspension insulators underwent field trials in 1964 and became widely available in the 1970s. They improved the insulation characteristics of transmission lines and reduced construction costs. Their acceptance into the industry was slow, until utilities realized the insulators could solve a major problem - vandalism. Polymer does not shatter when it is shot at. Even with a hole, it continues to insulate the line. Soon, utilities realized the lighter units also saved time and money on installation costs and, therefore, could be used for new construction.
Detroit Edison compared the Ohio Brass polymer insulator with the traditional porcelain insulator for the 345-kV Belle River-Jewell No. 2 transmission line completed in 1989. The utility saved from lower losses, reduced its maintenance and material, and pushed down installation costs by approximately US$4000 per mile. Soon, other utilities were requesting polymer replacement parts for substation porcelain. Today, not only are polymer line insulators available, but also polymer station post insulators, polymer-housed surge arresters, polymer bushings for transformers and breakers, and instrument transformers with polymer housings.
Underground Residential Distribution Because not all people can see the aesthetic appeal of an overhead distribution system, someone came up with the idea of placing residential distribution underground. This process was easier said than done. Nevertheless, utilities started going underground as early as the 1920s. Applications did not become widespread at that time, however, because of cost and the limited availability of equipment. At first, utilities placed pole-mounted transformers and switches in large enclosures and mounted them on pads at ground level.
Then, demand for the process increased in the late 1950s with the end of World War II. Troops returned home, married, started families and moved to the suburbs - areas that needed to be aesthetically pleasing. Underground residential distribution (URD) answered this need.
Later, URD met polymer chemistry and birthed a new technology. In the early 1960s, RTE worked with Elastimold to develop polymer/rubber insulator coverings for bushings, switch contacts and bus work. In 1960, RTE patented the Bay-O-Net fuse assembly and followed it up with a 1964 patent for the 15-kV load-break elbow terminator. An estimated more than 10 million of these products remain in service today. Together, these developments made the dead-front padmounted designs a reality. The connection of padmounted equipment to source and load was accomplished with an improved underground cable consisting of a conductor (copper or aluminum), insulation (polyvinyl chloride, polyethylene, ethylene-propylene rubber) and a jacket (nylon, chlorinated polyethylene). In addition to being out of sight, URD was not prone to outages in adverse weather. Although the concept sounds simple, it took decades to develop the dependability of URD that customers now enjoy.
The Silicon Age In 1947, Bell Laboratories invented the transistor - a product that represented quite an advancement in electronics because of its small size, low power consumption, low heat generation and high reliability. One of the transistor's first applications for utilities was relaying. Carrier communication equipment also used transistors. Then the 1900s saw the introduction of the electromechanical design. Solid-state relays incorporated transistors and diodes, and reference diodes came about in the late 1950s. Reference diodes worked faster than electromechanical devices and responded to line-to-ground, phase-to-phase and three-phase faults. Soon manufacturers were designing all protective relays as solid-state devices. Next, integrated circuits came about to improve relay abilities. Microprocessor technology followed in the 1980s. Microprocessors provided many benefits for protective relaying, including reliable operation with self-checking capability, fault location, event recording, local and remote reporting, and flexible applications due to programmability.
Power Electronics Transistors worked well for electronics, but power electronics needed something more robust. Early semiconductors tended to fail when they generated high temperatures. For power electronics, semiconductors needed to handle high currents and high voltage. Bell Laboratories developed a four-layer power diode in the mid-1950s using a silicon-based design. The company hoped this design could eventually replace the high-voltage direct current (HVDC) mercury-arc valve. Westinghouse also came up with a four-layer power diode using a Germanium-based design in about the same time frame and with the same intent as Bell Labs. Neither design resulted in market success. Therefore, research continued on both sides of the Atlantic for more suitable silicon-based electronic devices.
Industrial Applications In 1956, Siemens developed a manufacturing process for high-purity monocrystalline silicon. A GE engineer visiting the Siemens facility on an unrelated assignment brought a material sample back to the United States, and by the end of 1957, the silicon-controlled rectifier (SCR) was born. GE announced the SCR in the December 1957 issue of Business Week. The initial devices, rated around 1000 V, could support several hundred amperes of current. Today, modern thyristors can withstand up to 9000 V and tolerate currents of 4000 A.
HVDC Goes Solid State It took some time for solid-state technology to develop the thyristor valve. ASEA replaced one of the mercury-arc valves at the Gotland link with a thyristor valve design in 1970, which proved the concept. In 1972, GE built the Eel River back-to-back converter station in New Brunswick, Canada. It was the first solid-state HVDC scheme (320 MW at 80 kV) to use thyristor valves. From that point on, the thyristor became the technology of choice for converter station design.
Power Electronics and the Thyristor Once thyristor-valve technology became available, engineers found additional power electronics applications. The Static Volt Amp Reactive Compensator (SVARC) was the first device developed using the thyristor to control shunt-connected capacitors and reactors to control voltage without moving parts. In the 1980s, the Electric Power Research Institute (EPRI) started a program called "Flexible AC Transmission Systems" or FACTS. The Institute of Electrical and Electronic Engineers (IEEE) defines FACTS as an ac transmission system incorporating power-electronic-based and other static controllers to increase a transmission system's power-transfer capability and provide direct control of power flow over selected transmission paths.
Some of the more common FACTS devices in operation today include:
* STATCOM - Static Synchronous Compensator (an energy storage and absorbing device)
* SVARC - Static Volt Amp Reactive Compensator (a VAR generator and absorber)
* TCSC - Thyristor Controlled Series Capacitor (provides a smooth variable series capacitive reactance)
* UPFC - Unified Power Flow Controller (a series voltage source and a parallel voltage source operating together as a voltage source converter).
FACTS technology can control series and shunt line impedances, phase angle, voltage and current ratings, and power flow. FACTS technologies also address a myriad of power-quality needs.
Sulfur Hexafluoride Gas As polymers and silicon made inroads into technology, systems around the world saw increased load growth, which caused utilities to consider higher voltage lines. But before utilities could switch to extra-high-voltage (EHV) and ultra-high-voltage (UHV) installations, insulation systems had to attain quicker response times. Utilities also needed higher rated circuit breakers. Many interrupting technologies were available (oil, vacuum, air blast and air magnetic), but each had its own limitations. Fortunately, sulfur hexafluoride (SF subscript 6) gas became commercially available at this time and proved to be a better interrupting medium than those materials.
In the early 1950s, experimenters Brown, Strom and Lingal performed the first evaluations using SF subscript 6 gas as an interrupting medium. They used a plain air break and found they could improve the air break's interrupting capabilities by blowing the SF subscript 6 gas along the arc column. In 1953, Westinghouse introduced the first high-voltage load-break switch. It contained a sealed interrupter chamber with SF subscript 6 gas at three atmospheres. The arc was extinguished by something called a puffer interrupter, which was a piston assembly that mechanically produced a puff of SF subscript 6 gas to cool and deionize the arc caused by the parting contacts.
Puffer Technology and the Circuit Breaker By 1956, Westinghouse had developed the technology to the point of placing an actual SF subscript 6 power circuit breaker (with a 115-kV, 400-A, 1000-MVA rating) in service. The SF subscript 6 power circuit breakers had progressed to 230 kV, capable of interrupting 15,000 MVA. They were operating in the United States and Canada by 1959. The two-pressure SF subscript 6 breaker became fairly common to utility systems in the early 1960s. Technology continued to advance with the introduction of puffer breakers of both "live" and "dead" tank designs. Today, high-speed EHV SF subscript 6 power circuit breakers that use Teflon puffers are available for 362 kV up to 800 kV. The breakers can interrupt up to 80 kA three-phase, short-circuit currents in fewer than two cycles.
Puffer technology also found its way to distribution systems when it was applied to the circuit switcher developed by S&C Electric in 1959. SF subscript 6 gas quickly replaced multiple air gaps to interrupt the arc in early models of the circuit switchers. The improved circuit switchers filled a spot between the fuse and the fully rated circuit breaker in distribution substation design. The gas proved to be very economical and could be used for both switching and fault protection applications for transformers, shunt capacitor banks, shunt reactors, and line and cable switching. Today, it is hard to find a distribution system that does not use a circuit switcher in some capacity.
An Insulating Medium Along with SF subscript 6's arc-extinguishing properties, the gas offered engineers an insulating medium that could revolutionize transmission substation design - the gas-insulated substation (GIS). The basic principle of the GIS is that a metal enclosure houses the current carrying parts. Pressurized SF subscript 6 gas fills the space between the conductor and the enclosure, and SF subscript 6 breakers perform the switching. Transformers connect directly to the conductor within the pressurized enclosures. Polymer bushings filled with SF subscript 6 gas make the entrances and exits. The GIS' compact design made it ideal for areas with high levels of airborne contamination or other environmental problems. Research continued through the 1960s and 1970s. It culminated with the world's first 765-kV GIS facility, which was placed in service in 1979 by the American Electric Power Corp., Lynchburg, Virginia, U.S.
High-Temperature Superconductivity One of the most stimulating developments in material science was high-temperature superconductivity (HTS). Superconductivity was discovered in 1911 when a Dutch physicist, Heike Kammerlingh Onnes, passed a current through a wire of pure mercury at 4K (269C or 452F) and found the resistance had gone to zero. But it was not until 1986 that two Swiss physicists, Karl Alex Muller and J. Georg Bednorz, discovered certain ceramic materials that could retain their superconductivity at temperatures as high as 35K (238C or 397F). Continued research lead to the development of perovskite ceramic materials. These materials retained their superconductivity at temperatures greater than 130K (143C or 226F). For the first time, affordable liquid nitrogen could work as a coolant. HTS now has arrived, and our industry has been experimenting with it to develop new products for existing applications.
Superconductivity Partnerships The U.S. Department of Energy's (DOE) Superconductivity for Electric Systems Program is a collaboration of HTS research between government, private industry and universities. The program has identified two major technology goals to achieve HTS commercialization. The first goal is to solve the problem of manufacturing electrical wire from the brittle ceramic HTS materials. The second goal is to design electrical devices like motors, transformers, generators and cable to be able to use those wires. These partnerships enable vendors to tap into classroom material-science advances to build prototype devices, which they then place on utility systems to prove the feasibility of superconductor technology.
Superconducting Potential In 1996, one superconductivity partnership developed a 200-hp air-core synchronous motor with HTS field coils to prove HTS technology in a motor application. The motor exceeded its specifications by 60%. This year, a partnership is building a 1000-hp motor for testing and has scheduled a 5000-hp motor for testing in 2002. The DOE expects HTS motors to have efficiencies beyond 98%, which translates into reductions in losses by at least 50%.
HTS technology also is being used in transformer designs. In 1997, a partnership led by ABB installed and operated a three-phase, 630-kVA, 18.7-kV/420-V HTS transformer on an electric-utility system for one year in Geneva, Switzerland. Waukesha Electric Systems, which led another partnership, demonstrated a 1-MVA transformer that same year. Currently, another partnership is designing a 5-/10-MVA, 26.4-/4.16-kV HTS transformer. It's estimated that an HTS transformer will have a 45% lower weight and reduce total losses by 30%. Cooling by a medium like liquid nitrogen removes the fire risk of oilcooled units. HTS transformers will be a welcome addition in high-density urban areas.
First Industrial "Field Test" Of HTS System One of the more exciting applications of HTS technology is in high-capacity transmission cables. Currently, DOE partnerships are studying two HTS cables: a warm-dielectric design (the electric insulation is outside the thermal insulation and not exposed to the liquid nitrogen) and a cold-dielectric design (the electric insulation is exposed to the liquid nitrogen). Southwire Co., which has been leading the cold-dielectric projects, announced that its HTS cable completed 2000 hr of operation at 100% on Aug. 16. The project consisted of a three-phase, 30-m (33-yd), 12.5-kV, 1.25-kA power cable installed in Carrollton, Georgia, U.S. that supplied power to two of Southwire's manufacturing plants. Southwire reported losses of about 0.5% during transmission. A traditional cable has losses of about 5% to 8%. Just think about the thousands of miles of underground transmission cables in the United States alone. HTS cables would be able to handle up to five times the power of today's conventional designs.
Into the 21st Century Our industry is faced with deregulation and aging transmission and distribution systems. Most of these systems have far exceeded their designed lives. At the same time, demand is pushing transmission assets to their stability, voltage and thermal limits. Add to that the pressure to reduce capital expenditures and operations and maintenance costs. Without innovation, the future of T&D would look bleak. For the past 50 years, we have seen wars, price-fixing scandals, inflation, energy shortages and a global economy severely impact our industry. Yet each time, we have come out stronger. Improved material-science technologies have given us many tools to help improve the infrastructure. As long as laboratories continue to produce materials, engineers will continue to find unexpected ways to incorporate these materials into the system. More importantly, innovators will continue to find new ways to meet the demands of the 21 superscript st century customer.
Engineers first used evolution spark gaps to protect lines and substations from the effects of lightning. In 1920, lead oxide film was introduced. This was replaced in the 1930s by silicon carbide non-linear resistors with series gaps. Then in 1968, Matsushita Electric Industrial Co. improved a non-linear resistance material based on zinc oxide (metal-oxide-semiconductor). Originally, the company developed this material for the low-voltage/current electronics industry. In 1970, General Electric experimented with zinc oxide, increasing the Joule rating (energy absorption). Now, manufacturers offer zinc oxide surge arresters in all distribution and transmission voltage levels.
Zinc oxide technology can improve transmission-line operating performance. Duke Power Co. experienced an insulation flashover problem with its 100-kV Westminster B&W line in the early 1980s. Working with the Ohio Brass Co., Duke engineers analyzed this 17.3-mile (28-km) line and placed more than 40 intermediate-class zinc oxide arresters directly on selected transmission structures, eliminating flashover problems and reducing line trip-outs. Ohio Brass then developed polymer housings for arresters, producing a lightweight unit. The new units weighed 35 lbs (16 kgs) compared with porcelain units of 132 lbs (60 kgs). Its light weight allowed utilities to mount the polymer unit on structures without modifying those structures. We have come a long way from the spark gap of the past.
There was a time when all engineering calculations were done on slide rules. That changed in the early 1980s, when IBM introduced the PC Junior personal computer. The computer had an expensive price tag and limited capabilities, but was available to engineering departments. Not long after, programs developed that rivaled those on the utility's mainframe. Utility engineers could perform studies for transient stability, switching surge, lightning surges or insulation coordination.
The PC now has been used for everything from materials management, automatic meter reading (AMR), supervisory control and data acquisition (SCADA) systems, and programmable logic controllers (PLCs) to automatic mapping/facilities management (AM/FM). Utilities even offer their own intranet to authorized employees. Field personnel can access operation files, construction drawings, and manufacturer's drawings and instruction books right from their laptops. Engineers can monitor key pieces of equipment anywhere on the system without leaving their desks. Technicians can change relay settings from the shop without having to drive to the station. Computer assisted drafting (CAD) programs have given the designer three-dimensional capabilities in line and station designs. Since experienced engineers and technicians are hard to find, utilities, manufacturers, and consulting firms are forced to do more work with a smaller work force. Silicon has impacted the way we work.
Somewhere along the way, the term "SCR"(silicon-controlled rectifier) changed to "thyristor." Ed Owen, a historian at GE, says the name is a combination of "thyratron" and "transistor" or "thyristor." The thyratron was a 1921 modification of the mercury-arc valve by GE. It was formed from the Greek words "thyra," meaning "gate," and "tron," meaning "tube." In 1963, the Institute of Electrical and Electronic Engineers officially adopted thyristor as its name for the SCR.