Encyclopedia of Smart Materials (Vols 1 and 2) - M. Schwartz (2002) WW Part 11 pdf

0 −160 −80 0 80 160 0 Figure 29 Transverse strain along the stretching dir as a function of driving electric field at different tem measured for stretched P(VDF-TrFE) 68/32 mol% copo irradiated at 100◦ C with 70 Mrad dose using 1.2 MeV −S3 (%) 3 that are isotropic in the plane perpendicular to th field, the strain component in the plane is an a the strains along the chain (positive) and perpen the chain (negative) and is in general positive For electrostrictive materials, the electrom coupling factor (ki j ) has been derived by Hom et on the consideration of electrical and mechanica generated in the material under external field (9 2 1 kSj2 2 k3 j = 0 2 4 P2 (×10−3C2/m4) 6 (c) 80 E(MV/m) E (MV/m) (b) 0 40 PS + PE PS − PE + PS ln 1 − PE PS where j = 1 or 3 correspond to the transverse o dinal direction (e.g., k31 , is the transverse coupli D and s j j is the elastic compliance under constant tion, S j and PE are the strain and polarization r respectively, for the material under an electric The coupling factor depends on E, the electric fi In Eq (13), it is assumed that the polarization-fi relationship follows approximately −S3 (%) 4 |PE | = PS tanh(k|E|), 2 0 10 siD PE ln j 30 50 70 T (°C) Figure 28 (a) Electric field induced strain along the thickness direction (longitudinal strain, S3 ) versus electric field measured at room temperature and 1 Hz, (b) change in longitudinal strain (S3 ) with square of polarization (P), and (c) temperature dependence of longitudinal strain induced under 14 MV/m and 1 Hz driving electric field, of unstretched P(VDF-TrFE) 68/32 mol% copolymer films irradiated at 105◦ C with 70 Mrad dose using 1 MeV electrons where PS is the saturation polarization and k is a It is found that Eq (14) describes the P-E relat the irradiated copolymers studied here quite we The electromechanical coupling factors for t ated copolymers have been determined based on on the field-induced strain, the elastic modulus and polarization Presented in Fig 31 are k33 fo stretched sample and k31 for the stretched sam the drawing direction Near room temperature a an electric field of 80 MV/m, k33 can reach more which is comparable to that obtained in a sing P(VDF-TrFE) copolymer (81) More interestin 0.45 can be obtained in a stretched copolymer 0.2 25 20 30 40 50 60 0 70 0 10 T (°C) 20 30 Tensile stress (MPa) Figure 30 Temperature dependence of elastic modulus measured along the stretching direction for stretched P(VDF-TrFE) 68/32 mol% copolymer films irradiated at 100◦ C with 70 Mrad dose using 1.2 MeV electrons (b) 75 MV/m 1.2 (a) −S3 (%) 70 0.3 0.8 60 50 0.4 0.2 40 K33 30 20 0.2 0 21 °C 40 °C 30 °C 0.1 50°C 0.0 (b) 0 2 4 6 Hydrostatic pressure (MPa) Figure 32 Effect of (a) tensile stress on transverse stra stretched film and (b) hydrostatic pressure on longitud (S3 ) for unstretched film at room temperature unde driving electric fields The sample used here is P(VDF 35 mol% copolymer film irradiated at 95◦ C with 60 using 2.55 MeV electrons K31 0.4 0.2 25 °C 30 °C 0.0 0 40 80 120 E (MV/m) Figure 31 Dependence of electromechanical coupling coefficients on the applied electric field: (a) k33 for extruded unstretched P(VDF-TrFE) 68/32 mol% copolymer films irradiated at 105◦ C with 70 Mrad dose using 1 MeV electrons and (b) k31 for stretched P(VDF-TrFE) 68/32 mol% copolymer films irradiated with 70 Mrad dose using 1.2 MeV electrons at 100◦ C much higher that values measured in unirradiate TrFE) copolymers For a polymer, there is always a concern about tromechanical response under high mechanical l is, whether the material can maintain high st els when subject to high external stresses Fig depicts the transverse strain of stretched and i 65/35 copolymer under a tensile stress along th ing direction and the longitudinal strain of un and irradiated 65/35 copolymer under hydrostatic (100,101) As can be seen from the figure, under a electric field, the transverse strain increases init the load and reaches a maximum at the tensile about 20 MPa Upon a further increase of the field-induced strain is reduced One important fe vealed by the data is that even under a tensile 45 MPa, the strain generated is still nearly the CONCLUDING REMARKS A large number of studies are concerned with the electromechanical properties of PVDF and P(VDF-TrFE) polymers, including both the piezoelectric responses from polymers with semicrystalline and single-crystal forms and electrostrictive responses from the newly developed highenergy irradiated copolymers This article has consolidated these studies and emphasized the different polarization responses in ferroelectric polymers such as polarization switching, phase transformation, and pure dielectric response Optimizing the electromechanical responses from each type of polarization responses is a fruitful area of research By proper polymer engineering, the electromechanical properties can be improved substantially as demonstrated in the high-energy irradiated copolymers The discussion has included the syntheses, stereochemistry, and major crystal structures as well as their interesting morphologies, phase diagrams and phase transitions From a practical perspective, it should be quite evident that knowledge of their macromolecular properties and structures is quite desirable to successfully exploit their piezoelectric and electrostrictive properties In particular, the molecular conformation, crystal structures, and polymer morphology can be controlled at the molecular and mesoscopic levels, and this can be accomplished by varying the composition and electroprocessing conditions, as well as utilizing defect modification As a result, the properties of PVDF and its copolymer depend substantially on these conditions Although traditional PVDF and the P(VDF-TrFE) polymers have been used in the piezoelectric mode, recent evidence was presented that demonstrates a remarkable enhancement in the strain of P(VDF-TrFE) films after exposure to high-energy irradiation, which involves electrostriction Further study in this direction is certainly merited if only to identify alternative techniques to generate electrostrictive polymer films and other avenues to achieve high electromechanical effects BIBLIOGRAPHY 1 A.J Lovinger, Science 220: 111 (1983) 2 T Furukawa, Phase Transitions 18(2): 14 (1989) 3 H.S Nalwa, ed Ferroelectric Polymers Dekker, New York, 1995 4 T.T Wang, J.M Herbert, and A.M Glass, eds Applications of Ferroelectric Polymers Blackie and Son, Glasgow, 1988 11 H.R Gallantree IEEE proc 130: 219 (1983) 12 P.M Galletti, D.E De Rossi, and A.S De Reggi, e Applications of Piezoelectric Polymers Gordon a New York, 1988 13 J.B Lando, H.G Olf, and A Peterlin J Polym 941 (1966) 14 M.K Tamura, K Ogasawara, N Ono, and S J Appl Phys 45(9):3768 (1974) 15 R.G Kepler and R.A Anderson J Appl Phys 49: 1 16 M Tamura, S Hagiwara, S.Matsumoto, and N O Phys 48: 513 (1977) 17 D Naegele and D.Y Yoon Appl Phys Lett 33: 13 18 S.C Mathur, J.I Scheinbeim, and B.A Newma 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particularly many reports on a functionally graded ceramic, which can be called a smart material In this ceramic, the area of strong thermoelectric performance shifted with increasing temperature Then, thermoelectric performance can be kept high across a wide temperature gradient There have been some reports on functionally graded polymeric materials (2–38) These functionally graded polymeric materials can be classified into four types based on the materials used, as shown in Table 1 Then, graded structures may be classified into six groups However, reports on functionally graded polymer blends are few (4–9,14–25), although studies have been published on various types of blends A functionally graded polymer blend has the structure shown in Fig 1 The blend has two 100 times shorter than the “diffusion in melt state The optimum conditions can be easily determine our method has many controllable factors Furth ical decomposition of molecules does not occur ration because the preparation is at a lower tem Therefore, our method is considered very useful In this report, I give a detailed descripti preparative mechanism for functionally gra mer blends in the dissolution–diffusion meth I explain how I determined the optimum c for the several types of functionally graded blends, polyvinyl chloride (PVC)/(polymethyl met (PMMA), polyhexyl methacrylate (PHMA), or p lactone (PCL), and bisphenol A type poly (PC)/polystyrene (PS), in characterizing graded s of the blends by measuring FTIR spectra Table 1 Various Types of Functionally Graded Polymeric Materials Types of Materials Used Metal(or ceramic)/ Polymer Structure Composites Preparative Method r Laminate method r Electric field method r Centrifugation method r Flame spraying method Size of Dispersio Big r Surface inclination in Polymer/Polymer Immiscible polymer blend melt state method r Surface inclination in solution method r Dissolution–diffusion method r Diffusion in melt Miscible Molecular polymer blend method order r Dissolution–diffusion method r Diffusion method of Copolymer Atom–atom (ramdom) monomer in polymer gel Atom order (intramolecules) r Living anion or radical Copolymer (tapered) polymerization method r Changing method of Density of cross-linking cross-linking conc r Changing method of High-order Same atoms structure (same polymer) cross-linking temp and molec r Injection molding method Crystal structure Content of polymer A (%) Figure 2 Schematic model of dissolution–diffusion 100 0 the surface to the other, and those surfaces are of polymer A only or polymer B only 100 100 0 0 Position of measuring point Laminate Functionally graded blend Homogeneous blend Figure 1 Schematic model of functionally graded blend microscopic spectra, thermal behaviors around the glass transition temperature(Tg ) by the DSC method or by SEMEDX (Scaning Elecro Microscopy-Energy Disperisive Xray Spectrometer) observation Further, several types of functional properties, especially smart performance, are discussed, which result from the graded structure Finally, the prospects of functionally graded polymer blends for applications are discussed Third Type After the dissolution and diffusio mer A reaches the air side surface of the polym lution, polymer A and polymer B molecules beg with each other and become miscible The conc gradient begins to disappear The Formation of a concentration gradient de (1) the dissolution rate of polymer A in the polym lution, (2) the diffusion rate of polymer A in the p solution, and (3) the interrupted time of the diffu to the completion of solvent evaporation The fac control these phenomena are (1) the type of solve casting temperature, (3) the molecular weight o A, and (4) the amount of polymer B solution Until polymer A completely dissolves or reache face of the polymer B solution in the formation o and second types of structure, the diffusion of pol Graded structure 1 MECHANISM OF DIFFUSION–DISSOLUTION METHOD The mechanism of forming a graded structure is as follows After a polymer B solution is poured on a polymer A film in a glass petri dish, polymer A begins to dissolve and diffuse in the solution to the air side (Fig 2), but the diffusion is interrupted when all of the solvent evaporates Thus, a blend film is produced that consists of a concentration gradient of polymer A /polymer B in the thickness direction Based on the steps of dissolution and diffusion of polymer A, the graded structures can be classified into three types (Fig 3) First Type Polymer A begins to dissolve and then diffuses but does not yet reach the air side surface of the polymer B solution The blend has three phases (polymer A, polymer B, and a thin graded structure) Second Type Just when all polymer A has finished dissolving, the diffusion frontier reaches to the air side surface of polymer B solution The blend has one graded phase from Polymer B Narrow graded phase Polymer A Graded structure 2 Wide graded blend Graded structure 3 Gentle graded blend Figure 3 Schematic models of various types of graded 0.1 0.0 0 20 40 60 80 100 120 140 160 180 Distance from petri glass side (µm) Figure 4 The change in PVC content in the thickness direction of PVC/PMMA graded blends the polymer B solution is considered to obey Fick’s second law (Eq 1) by assuming that the evaporation of the solvent from the polymer B solution can be neglected during diffusion: ∂CA ∂ 2 CA = DAB r , ∂t ∂ x2 (1) where b is the distance between the petri glass su the other side of the remainder of polymer A, whi yet dissolved Therefore, the gradient profile in at t can be estimated from Eq (2) The fit of Eq (2) to the experimental data was for the PVC/PMMA graded blend, and this is in detail in the next paragraph The experime agreed approximately with the values predicted as shown in Fig 4 DAB and b were obtained as 6 and 57 µm, respectively The DAB was much la the value in the “diffusion in melt state,” and th that this dissolution–diffusion method is very us Further, a thicker and more excellently gra film can be prepared by the multiple step meth lustrated in Fig 5 Here, the graded blend was by repeatedly changing the composition of the bl poured solution 1 step method 4 steps method Evaporation of solvent The 1st step 2 steps method Evaporation of solvent Evaporation of solvent Polymer B solution Dissolution-diffusion Polymer A film Polymer A/Polymer B (5/5) solution Dissolution-diffusion Polymer A/Polymer B (7/3) solution Dissolution-diffusion Polymer A film Polymer A film Evaporation of solvent Evaporation of solvent Dissolution-diffusion Polymer A/Polymer B (5/5) solution Dissolution-diffusion Film formed in the 1st step Film formed in the 1st step Polymer B solution The 2nd step Evaporation of solvent The 3rd step Polymer A/Polymer B (3/7) solution Dissolution-diffusion Film formed in the 2nd step Evaporation of solvent Polymer B solution The 4th step Dissolution-diffusion Film formed in the 3rd step Figure 5 Schematic models of multiple step methods on a laminate, the PMMA content increased at 60% of the distance/thickness, and it was confirmed that it has a thin graded layer (about 10–20% of the distance/thickness) Then, in the blend of graded structure 3, the PMMA content was kept at about 50% in the entire range However, in the blend of graded structure 2, the PMMA content gradually increased in the range from 0–100% of the distance/thickness Thus, it was found that this blend had an excellently wide concentration gradient Here, the PMMA content was estimated from the ratios of the absorption band intensities at 1728 cm−1 (stretching of the carbonyl group in PMMA) and 615 cm−1 (stretching of C–Cl bond in PVC) The change in PMMA content in the thickness direction of the blend film was estimated by measuring FTIR-ATR spectra on a sliced layer of the blend film The change in PVC content of the graded blend can be characterized by Raman microscopic spectroscopy method, similarly to the FTIR-ATR method, as shown in Fig 4 Raman microscopic spectra were measured at the focused point, which was shifted by 10 µm from one surface area to the other It was confirmed that the blend had a comparatively thick layer of a graded structure phase This method is considered significantly useful because an easy and detailed estimate can be made for the graded profile of a blend Further, the graded structure was characterized by the DSC method The DSC curve of the blend that has a widely graded structure (graded structure 2), shows more gradual steps around Tg than the others (Fig 7) Similarly, Temperature (K) Figure 7 The DSC curves of several types of PVC/PMM the structures of the samples, which were prep der several types of conditions were investiga the optimum conditions (molecular weight of PV 35600, MW = 60400; type of solvent: THF/tolu volume of solvent:0.23 mL/cm2 ; temperature: 33 determined In the PVC/PHMA system (7), the graded of the sample could not be estimated by the F and DSC methods, because PHMA was very sof temperature Thus, the graded structure was mea the SEM-EDX method (Fig 8) The chlorine cont sample increased gradually to the petri glass side, it was confirmed that it has a widely graded stru Further, the structures of the samples, which pared under several types of conditions were inve and the optimum conditions (molecular weight Mn = 35600, MW = 60400; type of solvent: MEK of solvent: 0.37 mL/cm2 ; temperature: 313K) we mined Amorphous Polymer/Crystalline Polymer Miscible B In the PVC/PCL system (25), we obtained the conditions for preparing a graded polymer bl had a wider compositional gradient, similar t Graded structure 1 Graded structure 2 Graded structure 3 80 60 Chlorine content PMMA Content (%) 100 40 20 0 0000 0 20 40 60 80 100 (Distance from petri glass side)/(sample thickness) (%) Figure 6 The change in PMMA content in the thickness direction of several types of PVC/PMMA graded blends 15 kV Thickness direction Figure 8 Chlorine content along the thickness of a P graded blend (X 750, —; 20 µm) Distance from petri glass side (µm) Figure 9 Graded structure of PVC/PCL graded blends Figure 11 Graded structure of PVC/PCL graded blen content; ◦, heat of diffusion) the PVC/PMMA system Figure 9 shows the PVC content of the samples in the direction of thickness, measured by the FTIR-ATR method PVC began to decrease at about 70 µm from the petri glass side and decreased gradually until the surface of the air side, that is, about 240 µm away from the petri glass side in both solution volumes Then, the change of Tg in the thickness direction of the blend film was characterized by the DSC method (Fig 10) for 0.364 mL/cm2 of solution volume Tg decreased at increasing distance from the petri glass side, similar to the PVC content Thus, the graded structure in PVC content was confirmed by the graded profile in Tg Further, the change in PCL crystalline content was determined from the amount of heat diffusion of crystalline PCL, measured by the DSC method The heat diffusion began to increase, after it was kept at zero until about 130 µm of the distance Then, it increased immediately at about 180 µm Thus, it was found that a graded structure in crystalline PCL was formed in the range from 130–240 µm of the distance This means that the graded PVC/PCL blend obtained had both a gradient concentration of PVC and a gradient content of crystalline PCL, as shown in Fig 11 The PCL content was about 30% at about 130 µm of the distance This result indicates that crystalline PCL in the homogeneous PVC/PCL blend emerged at concentrations of more than 30% PCL (39) Then, it was concluded that the amorphous phase was made of a miscible amorphous PVC/amorphous PCL blend Further, the PCL c phase decreased again coming closer to the s the air side It is thought that this phenomen because the formation of the amorphous phas thermodynamically stable than that of the c phase Therefore, it was believed that the graded of the PVC/PCL graded blend is as schematic trated in Fig 12 Amorphous Polymer/Amorphous Polymer Immiscible Blends We attempted to prepare a graded PC/PS the dissolution–diffusion method (24), simila PVC/PMMA system In this case, PS solution w on PC film However, we did not obtain a grad ture, but we did obtain a system of two homogen ers which were composed of about 50% and 0 as shown in Fig 13 Then, macrophase separ observed in the former layer It is believed that th because of only three factors, the dissolution rate rate, and evaporation time affect the process of graded structure of a miscible blend However, in graded structure of an immiscible blend, three ne macrophase separation, surface inclination, and try, in addition to the former factors may significa the process, as shown in Fig 14 It is especially c 100 90 80 70 60 50 40 30 20 10 0 340 320 300 280 Tg (K) PVC Content (%) 360 260 240 220 50 100 150 200 Distance from petri glass side (µm) 200 250 Figure 10 Graded structure of PVC/PCL graded blends ( r, Tg ; ◦, PVC content) PCL Crystalline phase PCL Figure 12 Schematic model of PC/PS graded b SMART SENSORS (2) converting mechanical energy to electrical en (3) electricity delivery The environments charac each sector are summarized in Table 4 For the of this article the second and third functions a enough in their environments that they are dis gether as electricity systems in what follows The first prerequisite for SMS in the power is that they be able to perform reliably in the ment That is, they must produce accurate sign normal as well as perturbed conditions for prol riods of time Again, their priority is to inform authority that there is a problem or that dama curred, and where Autonomous action can als of the SMS mandate; electricity systems are qu dant, for example, so a smart sensor could init down of a redundant component that is about t a report of illness is the primary responsibility seen, most smart sensors intended for power-ind plications are based on fiber optics because of th nity to electromagnetic interference (including strikes and ground faults), as well as their smal light weight Requirements and Scope Thermal Plant Environments Need for Better Measurements In recent years, advances in electronics (signal processing and conditioning) have resulted in improved instrumentation and controls for power plants Many utilities have replaced analog and pneumatic controls with distributed digital control systems (DCSs) in order to reduce operating costs and to increase the capability to respond to system dispatch A DCS can regulate processes with less than 0.25% uncertainty, compared with 2% to 3% uncertainty for analog controls However, the conventional sensors used in power plants cannot, without frequent calibration, provide the levels of accuracy appropriate for sophisticated DCSs Thus, smart sensors offer the means to increase measurement accuracy and thereby realize the benefits of DCSs Opportunities for better measurements are numerous in every sector of the power industry For example, Sachdeva (4) lists 1393 essential sensors in a typical 500 MW coal-fired power plant Of these, approximately 1150 are devoted to sensing temperature and pressure In forward-looking utilities that are developing methodologies for early diagnosis of problems, monitoring of critical components has resulted in 4000 sensors in some generating units (5) Likewise, an NSF workshop (6) identified Pressure Sensing Many pressure transmitter stalled in power plants rely on fill fluids to sep cess fluids from the gauge mechanisms These d subject to failures when fill fluids leak, failure difficult to detect In addition, all conventional sensors drift with time, a condition that necess proportionately large efforts to restore accuracy ify operability These concerns have prompted a ment of modern sensor technologies to select cand adaptation to use in power plants (7) Among th is the conclusion that fiber-optic pressure sens provide more extensive sampling of process pres improved mode of signal transmission and proce freedom from electromagnetic and radio-freque ference in nuclear and fossil-fueled steam plants As a step toward implementing improvement sure sensing, a fiber-optic transducer based on t bend attenuation of light transmitted through fiber (Fig 1) has been developed (8) Since the d deflects linearly with pressure, process pressur sured by the diminution of light transmission th aluminum-coated fiber with core/clad/coating d of 150/180/210 µm Performance of the transd or because electrically based SMS cannot function properly in intense electromagnetic fields Second, the spatial extent of electricity systems dictates that the most urgent job for SMS is to detect damage or deviant conditions and report the location to a central authority Autonomous actions by SMS are less important The SMS constituent that matches this requirement is smart sensors In fact, smart sensors are the aspect of the SMS that has been most thoroughly investigated for utility applications Here, transference from another industry was vital: without the R&D base built by the communications industry, the technology of fiber-optic sensors might not have matured Undoubtedly, a wide variety of power industry problems will someday be addressed by truly smart, autonomous, fully integrated SMS At this juncture, however, the main thrust for SMS in utility systems has been aimed at developing and applying smart sensors and, to less extent, smart sensor-actuators Electricity delivery r Transformers r Switchgear r Overhead transmission r Near-ambient temperatures and pressures r High electrical and magnetic fields r High electrical currents through contacts r Often far from central control lines r Underground cable characterized in laboratory and field trials at pressures to 22.75 MPa (3300 psig) and temperatures to 438◦ C (820◦ F), with measurement error calculated to be 1.2% of full scale This smart sensor, developed for coal liquefaction service by the U.S Department of Energy, would be suitable for pressure measurements in nucle generators Strain Measurement Strain sensing as an of structural health in high-temperature comp Diaphragm 30 mm Weld Spacer Microbend sensor Pressure Diaphragm Cylinder Input Optical fiber 42 mm Bolt Output Weld Sensor detail Packing seal Flange pressure seal Steel tubing Optical fibers Figure 1 Diagram of the fiber-optic pressure transducer (8) 2×2 Coupler Lamp Figure 2 Schematic of interferometric strain sensor (9) becoming more important as power-generating equipment ages Conventional foil and wire strain gauges are not reliable at temperatures above 250◦ C (482◦ F) for long times, largely owing to the unavailability of adhesives that can withstand those temperatures Therefore, a fiber-optic sensor to monitor strain in boilers, headers, steam pipes, and other high-temperature structures has been developed for operation at temperatures up to 650◦ C (1202◦ F) Based on the Fabry-Perot interferometric technique, the system is shown schematically in Fig 2 A broadband optical beam is conducted into a quartz tube containing two fibers, each with a partially reflecting mirror at the end A small air gap or resonance cavity between the two mirrors forms an extrinsic Fabry-Perot interferometer (Fig 3) Beams reflected from the two mirrors interfere, travel back toward the detector, and enter an optical wedge (Fizeau analyzer) Reflected light from the FabryPerot sensor is transmitted maximally where the optical path length matches the dimension of the Fabry-Perot cavity Thus, when strain changes the cavity length, there is a corresponding shift in the intensity maximum transmitted through the optical wedge A linear photodiode array at the back of the optical wedge detects the transmitted beam Because this is a frequency-modulated sensor, it is insensitive to light attenuation; the signal reaching the photodiode array need only contain enough information for decoding (10) Partiallyreflecting mirrors Coating Transmitter/receiver fiber Epoxy Air gap (fabry-perot cavity) Target fiber Fused joints Quartz tube Figure 3 Schematic of Fabry-Perot interferometer (9) This small, lightweight device has been field two applications at a power station: a spot we main steam line operating at 565◦ C (1049◦ F), thermowell inside a reheat steam line at 538◦ C Feasibility of on-line monitoring of strain in stru high temperatures was clearly demonstrated Measurements with Fiber Bragg Gratings A p more versatile sensor technology is emb wavelength-modulated fiber Bragg gratings (FB are created in low-cost, commercially available fib FBG reflects a characteristic wavelength that c the grating periodicity changes with temperatu strain Research sponsored by the power ind concluded that, in principle, FBGs can serve a transducer elements to measure temperature, strain, vibration, acoustical disturbances, elect magnetic field strengths, and the concentrations chemical species (11) A primary issue in developing FBGs for util high-temperature environments is their stabil sures to high temperatures and temperature cy demonstrated that FBGs are quite robust: FBG long-time cycling between ambient and 427◦ C without degradation Use temperature can be to 650◦ C (1202◦ F) only if very low loads (strain posed on the fiber (11) FBGs for measuring tem pressure, and strain are now in prototype develop though several approaches to chemical sensing w have been explored in laboratory studies, they a ready for prototyping Sensors for Combustion Processes Accurate an sensors for very high temperature environmen have multiple benefits for thermal plant: avoidan age to heat-transfer surfaces, combustion contr dividual burners (not possible at present), red noxious emissions, and structural health mon critical components, to name a few The chief developing smart systems based on fiber optics fo tion environments is the temperature constrain fibers Fiber function is limited by the temper tion in combustion gases and superheated water environments (9) One especially important challenge for hightemperature sensing is management of emissions from combustion In control systems for nitrogen oxides (NOx ), ammonia (NH3 ) or urea (NH2 –CO–NH2 ) is injected into combustion gas to react with NOx and produce molecular nitrogen and water Postcombustion NOx reduction must avoid significant NH3 in the exhaust, both to comply with emission regulations and to keep from fouling downstream components A feedback control system is needed, but no reliable, real-time NOx or NH3 sensors have been available An investigation is exploring measurement of nitric oxide (NO) levels on the basis of radiative emissions from single molecular transitions that are well separated from emission features associated with other constituents in the flow The system consists of feedback-stabilized, scanning Fabry-Perot interferometers linked with thermoelectrically cooled wavelength detectors A digital system controls cavity lengths for wavelength scanning One detector monitors NO upstream of the injection plane and a second monitors NH3 downstream Signals from both are fed into the injection system controller, which then determines in real time the quantity of NH3 or urea to be injected for optimal NO removal Tests of the prototype system are underway at a utility power station (9) pH Measurement Corrosion behavior of steam-plant materials is determined to a large extent by the pH and electrochemical potential of the circulating water Since the physicochemical properties of water are highly sensitive to temperature, there is strong incentive to develop on-line sensors for pH that can be used at system temperatures, rather than relying on analytical extrapolations from grab samples cooled to ambient, as is the current practice However, attempts to develop on-line sensors for pH at elevated temperatures must confront two problems: degradation of the sensor materials by hot water; and, in the high-purity water characteristic of cooling loops, interactions of the sensor with the water can affect the pH being measured A sensor was developed by incorporating a pH-sensitive organic dye (8-hydroxypyrene-1,3,6-trisulphonic acid) in a polyacrylamide polymer at the end of an optical fiber (Fig 4) By choosing a dye with two absorption peaks, the sensor indicates the pH as the ratio of the two peaks; long-term leaching of the dye does not compromise the O-ring HPTS polymer Nylon mesh Figure 4 Schematic of the fiber-optic pH sensor measurements pH determinations were made su over the course of a one-year immersion at 38◦ C and pH changes associated with addition of 1 ppm line were measured consistently (12) Water at higher temperatures exacerbates problems for fiber-optic reflectors A 250 nm th tilayer (titanium–platinum–gold) coating for sap found to be stable to 180◦ C (356◦ F) In conjunc an azo chromophore (dinitrophenyl-azo-naptho indicator, pH was measured reproducibly in th tory for 160 hours at 50◦ C (122◦ F), which was t ity limit of the cellulose acetate waveguide (13 case, azo-based indicators are stable only to abo (212◦ F) While none of the pH-sensing systems d far are acceptable for use in high-temperature w liminary experiments have shown that a copper cyanine chromophore is stable to at least 200◦ C It is expected that the next step, an incremental ment, will be a fiber-optic pH probe that is usable (302◦ F) Electricity Systems Environments Distributed Fiber-Optic Temperature Sensor (DF sulator temperature is a key factor in the safe an operation of motor and generator windings, tran circuit breakers, underground cables, and overhe mission lines Although temporary overload cond not normally cause thermal damage to conducto than normal temperatures do have a cumulative shortening insulation life On-line methods to lo measure “hot spots” have traditionally not been largely owing to the fact that most transducers trically based In other words, conventional se vices are usually incompatible with the enviro an electrical system Furthermore, local tempera surements (e.g., 0.1 m [4 in] long or less) need to throughout an electrical system that may be hu meters (feet) long Motors, Generators, and Circuit Breakers To address this challenge, the DFOTS system has been developed for detecting hot spots in low-temperature (≤150◦ C [302◦ F]), high-voltage environments It is based on optical time domain reflectometry (OTDR), which was devised by the telecommunications industry for fault location in fiberoptic telephone lines A light pulse transmitted by an optical fiber is gradually attenuated by absorption and Rayleigh scattering The scattered light returns in a direction opposite to that of the injected light pulse To make a DFOTS, the fiber must be modified along its length such that the local backscattering changes as a function of the local temperature change This was accomplished by coating the fiber with a UV-curable polymer that changes refractive index reversibly with temperature (14) A change in the local intensity of backscattered light serves as a sensitive indicator of temperature, and the elapsed time of the returned pulse indicates the location of the temperature change, as shown in Fig 5 The DFOTS system has monitored winding temperatures in rotor and stator windings of motors and generators in trials at power plants (15) and in switchgear (14) It is accurate to within 5◦ C (9◦ F) over the range 0 to 150◦ C (32 to 302◦ F) A 100 ps laser pulse is capable of resolving hot spots only 2 cm (0.8 in) long over a fiber length of 40 m (131 ft) In retrofit applications, the DFOTS fiber can be strung between windings bars and slot wedges; in new windings, the sensor can be incorporated in the high-voltage groundwall insulation in direct contact with the conductors In either application, impending generator problems could be diagnosed rapidly and major winding failures prevented Improved remaining-life assessments would also ensue from knowing real thermal histories of insulation Underground Cables A similar DFOTS has been devised for temperature monitoring of underground power cables The power transfer capability of a buried cable is strongly affected by thermal conditions along the length of the circuit: burial depth, ambient earth temperature, soil thermal resistivity, and the like Power transfer could be optimized if actual temperatures along the cable are known in real time When a sharply pulsed laser beam (1050 nm) is injected into a standard multimode fiber, very weak, thermally dependent, molecular vibrations produce reflections are housed in slots in the stator core At the en adjoining the active length of the machine, pairs tors are linked by end connections to form coils plete set of end connections at each end constitut winding End windings cannot be supported as s the conductors, which are in slots; if blocks and become loosened by the forces of starting and st system faults, the end windings can vibrate and sively damage insulation Undetected end-wind tion can lead to a forced outage in a relatively s Standard strain gauges (metal foil or wire) canno in the strong electromagnetic environment of an generator A fiber-optic sensor based on microbending ha veloped to measure strain in end windings duri tion (9) The sensor attaches directly to an end converts deflection to strain Output of the devic over the range ±1000 µm/m (1000 microstrain 100 Hz, with a resolution of ±5 µm/m Monitoring Transformers Substation transfor large, oil-filled devices and are among the most components in an electric-power network The co ure, or an outage to repair a unit, can exceed th cost of the transformer within five days if the placement power from a less-efficient station is a Deterioration of transformer oil results from temperature, aging, and electrical discharges th oil Oil has an effective lifetime of about on hours at 90◦ C (194◦ F) but only about 100 hours (356◦ F) Winding Temperatures In principle, temper transformer windings could be measured by DFO on Rayleigh or Raman backscattering However, i found that transformer oil penetrates the fiber j is absorbed by the polymer cladding of Rayle sensors, and all-silica Raman-based sensors h equate spatial resolution (about 5 m [16.4 ft] present stage of development Point monitoring ing temperatures in real time is the best tha done right now by measuring the temperature-d fluorescent decay time of a photoluminescent sen rial (manganese-activated magnesium fluoroge Pulses of blue light power the phosphors; flu returning in the all-silica fiber is detected a preted in terms of sensor temperature (17) D is a well-characterized, intensity-dependent pr RF and US signals: the RF detector responds first, followed by the US detector The time interval between them depends on the distance from the partial discharge to the integrated detectors Only a series of paired RF and US signals with the same time interval is accepted by the signalprocessing circuitry as an indicator of partial discharge (18) The US sensors are specially fabricated from lead zirconate titanate (PZT) ceramic-epoxy composites that are tailored to have resonant frequencies in the range 200 to 400 kHz, which is above core magnetostriction spectra and below the AM broadcasting band After suitable encapsulation, the PZT composite is mounted and integrated mechanically with the RF detector, a compact annular metal ring (18) This device is unaffected by contact with transformer oil and functions over the temperature range −10 to 120◦ C (14–248◦ F) Voltage and Current Measurements Knowledge about electric fields and currents in generators, transformers, and power lines is of obvious importance to the power industry, not only for understanding normal behavior of system elements but for identifying defective or malfunctioning apparatus Optical sensors for voltage have in the past been based on electro-optical crystal transducers (e.g., bismuth germanate) that exhibit linear birefringence in electric fields (Pockels effect), which can be detected by a suitably polarized light beam (19) Pockels effect sensors have not yet been miniaturized, a step that would be required for distributed sensing Another approach to measuring electric fields is through electrostatic forces, which arise from electron rearrangements in conductors subject to external electric fields Charges induced at conductor surfaces interact with the external field to produce weak electrostatic forces normal to the surface By constructing a variable-gap Fabry-Perot microsensor as a conductive Faraday cage with a flexible silicon diaphragm (Fig 6), these forces can be measured quite accurately (20) Dual-wavelength referencing makes the sensor system insensitive to bending and transmission losses in the fiber; electric field strength is thus related to change in the intensity ratio at two different wavelengths dc fields from 0 to 500 kV/m and ac fields for energizing voltages up to 80 kV were successfully measured This device is a microsensor suitable for emplacement at important locations throughout an electric-power system Almost all optical sensors for current rely on the Faraday effect, which is circular birefringence (i.e., a difference in refractive index for left and right circular Top view Silicon 300µ 400µ Anodically bonded surface Aluminum film Pyrex Section A−A′ Figure 6 Fabry-Perot microcavity for measuring elec (a) Top view and (b) cross section (20) polarization) that is proportional to the magneti sociated with current flow Commercial fiber-opti sensors (Square D Company) have been shown liable at utility switchyards: metering accuracy from 100 A to 1400 A and 0 to 40◦ C (32–104◦ F) ture range (21) As with Pockels-effect sensors, rotation transducers are still bulk optical device Chemical Sensing Ensuring compliance with mental regulations that govern stack-gas emissio streams, and process streams will require real situ, monitoring methods Currently, samples are stored, and transported from the field before they lyzed in the laboratory Thus, analyses are neith nor always reliable, since samples can change ch between collection and laboratory Fiber-optic sensing is one remedy for this problem An optical chemical sensor consists of a chemi sitive indicator and a physical transducer The ind teracts with the chemical species of interest (ana undergoes a reversible change in absorbance, refr dex, polarization, and the like, that is a function in the analyte The transducer converts this optic into usable information One embodiment of thi logy is a fiber-optic hydrocarbon sensor (FiberCh Portions of the conventional (low refractive index are replaced by thin metal coatings with the de lective affinity and refractive index Typical res common hydrocarbons are shown in Fig 7 Sen in the low ppb range and hydrocarbons can be Time (5 second intervals) Figure 7 General response of fiber-optic chemical sensor to hydrocarbons sensors After six months in actual service, the s mained functional, with no measurable drift or for recalibration SMART SENSOR-ACTUATORS and quantified in vapors, droplets, thin films on water, dissolved in water, or as water-hydrocarbon emulsions (22) Structural Integrity of Dams Dams for hydroelectric stations, whether concrete or rock filled, are very conservatively designed Nevertheless, seismic events or other unforeseen geologic instabilities can threaten structural integrity The consequences of failure are so severe that early warning of malfunction or collapse is vital Embedded fiber-optic sensors are a logical answer Feasibility of this approach was demonstrated by installation of over 6.4 km (4 miles) of multiplexed simple and multifunction fiber sensors in a 7.5 MW dam during the construction phase (23) Over 90% of the embedded fibers survived placement, casting, pouring, and curing of the concrete, as well as framework removal and installation of generating machinery Among the embedded fiber optics were sensors for simultaneous monitoring of water pressure and vibrations at structurally critical locations Baseline vibration signatures were determined by statistical interpretation of speckle patterns (24) During “shakedown” of the facility, comparison of baseline vibration spectra with dynamic output of sensors within the powerhouse structure identified a vibration spike that was attributed to an out-of-round main gear in the power train Replacement of the gear eliminated the troubling vibration Dams are a likely venue for a more complete smart system: self-repairing concrete Dry (25) has developed several variations on the theme of injecting hardenable liquids into concrete One that is completely autonomous involves embedding hollow glass fibers filled with adhesives in the concrete Overloads on the concrete create microcracks that break the fibers, release adhesives into the cracks, and result in concrete as tough or tougher than the original Fiber optics will still be needed to detect such occurrences and report their locations to a central authority Structural Behavior of Wind Turbine Blades Windmills are large composite structures, usually located at remote sites, and subject to strong dynamic loads In-service inspection involves dismounting the blades, a lengthy and Several classes of smart materials can functio bined sensor-actuators: piezoelectrics, electro magnetostrictives, and shape-memory alloys Eventually, smart materials in all of these categ find roles in utility systems Up to the present t ever, interest in applying smart sensor-actuators industry concerns has been mostly focused on S ing in part to the large reversible deformations forces obtainable with SMAs, and in part to the of SMAs to perform actuations (shape changes only by the thermal environment, that is, withou sion In this regard, incorporation of SMAs in u tems is a step toward autonomous responses, whi set high-cost maintenance labor to some degree of applications that have been tested in prototyp in Russia, Ukraine, and Scandinavia, follow Compression of Transformer Cores Electrical coupling in large transformers is im compressing the core layers During convention facture, the core is compressed between the yoke ening the bolts, and the entire assembly is then to alternate cycles of vacuum and kerosene spray (257◦ F) to remove air from between the core shee core layers, compact, the compressive forces de that when the assembly is taken out of the vacu ber, some air reenters the core stack and optimum is lost Somehow, the maximum compressive pre to be maintained during the heating cycles M yoke bolts out of SMA can, in principle, remedy lem, as depicted in Fig 8(a) Properly designed S axially prestrained, transform during heating i and maintain pressure as air is sucked out, as demonstrated in Russia (27) A difficulty with thi stems from the large bolt sizes (50–75 mm [1.9 diameter), which makes homogeneity and heat of the SMA problematic An alternative has bee in Sweden that involves conventional steel bolts ries of precompressed SMA studs between the core package, Fig 8(b) As temperature is rais Yoke Core Bolts Figure 8 Transformer core compression with SMA elements (27): (a) Yoke bolts; (b) studs vacuum chamber, the studs expand axially to maintain well-distributed pressure (27) Inducing Compressive Stresses in Pipes The basic idea is to apply circumferential compressive forces on critical regions of piping to counteract tensile stresses caused by welding and service loads One such arrangement consists of axially extended SMA wire wound on slotted sleeves The sleeves are slipped on the pipe, positioned over at-risk circumferential welds, and heated above the transformation temperature of the SMA wire (27) Since the operating temperature of the pipe is also above the SMA transformation temperature, stresscorrosion cracking is forestalled and propagation of preexisting cracks is inhibited by the resulting compressive stresses In addition, pipe ends are prevented from separating should a break occur This application, intended mainly for nuclear power plants, has been tested in Sweden Mitigation of Erosion Caused by Cavitation and Liquid Droplets Cavitation ensues when the local pressure in flow field falls below a critical value that is a of temperature, surface tension, vapor pressure ternal pressure Vapor-filled cavities or bubble the liquid at regions of low pressure and co they move into regions of higher pressure Bu lapse is associated with very intense local impu can be destructive to nearby solid surfaces M subject to cavitation erosion and closely relate droplet erosion include boiler feed pumps, valves lation pumps in pressurized-water reactors, hyd runners and guide vanes, and last-stage blades turbines An investigation conducted for EPRI showed th basis of their anomalous resistance to low-cycl near-equiatomic alloys of nickel and titanium ( very resistant to both cavitation and liquid-drople High resistance to fatigue and erosion is ascriba ability of NiTi, either as austenite or martensite, reversibly without accumulating much residual d the constituent crystallites Since building large entirely out of NiTi is impractical, thin plates of N explosively bonded to structural steel and the e sistance of the resultant clads was demonstrate indicated by Fig 9 40 35 Aerial power lines sag when they are warmed by high electrical loads, especially in combination with high ambient temperatures Performance is degraded when overhead lines sag to the extent that ground capacitance becomes excessive This is a difficult problem, given the many thousands of miles of transmission lines A solution that is being tested in Canada, Ukraine, Russia, and Japan has several embodiments (27,28); a typical one is to attach an SMA member electrically and mechanically in parallel with the overhead conductor At low temperatures, the martensitic SMA is easily extended in tension Upon heating, however, the SMA reverts to the strong austenitic phase and shortens, forming a loop in the overhead conductor and thereby maintaining acceptable ground clearance Mass loss, milligrams Sag Control of Overhead Conductors 304L 30 CA6−NM 25 FER−255 20 15 10 5 Niti/Steel 0 −5 0 5 10 15 20 25 30 35 Time, hours Figure 9 Comparison among cast austenitic steel wrought stainless steel (304L), duplex stainless steel ( and NiTi cladding on steel in vibratory cavitation Fuses and fuse protectors Thermomarkers Switches and valves Bolted electrical connections Thermal actuators for valves, clutches, dampers, and flues Steam pipe hangers Steam trap flush Plugs in pipe ends and tubesheets De-icing of transmission lines Bolt breakers cascade of latches unnecessary Similar to circuit breakers, SMA fuses are advantageous in that they can be reset Quick-acting fuses for lightning protection can blow when heavy line usage causes a temperature rise An SMA shunt, normally open, closes during heavy usage, thereby avoiding a premature blow SMA flags bend at a predetermined temperature and signal which phase has blown or which electrical joint is hot Typically, SMA spring operates against a bias spring: under normal conditions the bias spring is stronger than the SMA spring; heat causes the SMA spring to transform, overcoming the bias spring, and operating the switch or valve SMA washers in Belleville configuration under bolt heads maintain contact pressure when thermally activated by increased contact resistance Applied in transformer connectors, aluminum buses, and disconnects Linear motion devices rely on shape recovery of prestrained SMA elements They are initiated by externally controlled electrical heating of the SMA Typically, bias springs reset these devices to their default positions Traditionally, a three-spring device with complicated mechanical linkages provides constant support under thermal conditions Can be replaced by a single SMA rod or a stack of SMA Belleville washers When a trap fills with condensate, a bimetal-actuated mechanism opens the trap The linear motion of the actuator allows leakage before full opening or closing SMA Belleville washer is faster and nonlinear, so leakage does not occur Pre-strained SMA plugs are inserted cold, then heated to form leak-proof seals Externally energized SMA devices apply cyclic loads to overhead conductors to de-ice them Explosive bolts are used in safety mechanisms in nuclear power plants and petrochemical plants They can be accidentally discharged under electrical fault conditions Pre-strained SMA tubes can serve the same purpose by breaking notched bolts during shape recovery Other Applications of SMAs A variety of concepts involving SMAs have been suggested as solutions to power-industry problems Some that have been demonstrated under laboratory conditions or evaluated in engineering analyses are described briefly in Table 5 (31,33) (28,31) (27,31,33) (27,28) (32,34) (27) (33) (32) (28) (31) CHALLENGES AWAITING SMART MATERIALS SOLUTIONS The preceding two sections describe application sensors and smart sensor-actuators to power problems Besides their favorable impact on u erations, these applications are important ste tion by smart materials and systems are listed in Table 6, which is meant to be illustrative, not inclusive Each problem is identified in the first column and a subjective ranking of severity is provided in the second column The last column differentiates among innovations for which most of the constituents are at least in prototype (near-term), those that are only partially in prototype (midterm), those in early proof-of-concept stages (long-term), or intriguing concepts (vision) perhaps without solution by smart systems Five of these challenges, chosen because they represent the whole spectrum of power-industry needs and possible solutions with smart materials, are discussed briefly in the balance of this section Real-Time Condition Assessment of Equipment A topic of major concern for utilities is in-service deterioration of critical components (35) Detailed information about equipment condition is an essential part of lifemanagement programs for generating units; such information also provides early warning of structural impairment, and therefore it is crucial for avoidance of forced outages Obtaining that information is a serious challenge For example, it has been estimated that about one-half of all forced outages in steam-generating plants are caused by corrosion Whereas generalized corrosion is readily detected and measured, environmentally induced cracking (e.g., stress-corrosion cracking and corrosion fatigue) is hard to detect and respond to Damage caused by creep and creep-fatigue is even more difficult to assess Another aspect of condition assessment is remaininglife analysis Nowadays, many utilities opt to keep a component in service after the expiry of its “design life.” In order to do so without jeopardizing personnel safety or system reliability, the following quantities must be determined (36): the amount of damage currently in the component, the rate that damage is accumulating, and the degree of damage that will cause failure At least three factors inhibit those determinations First, the amount of damage or size of the largest defect (depending on the damage type) may be hard to measure; where to look and what might have been missed are subsets of this difficulty All traditional inspection technologies suffer from inaccessibility constraints, such as, detecting corrosion of reinforcing bars in concrete or finding creep-fatigue cracks inside steam-turbine rotors Second, actual material properties can be hard to measure, especially without destroying the component This is a principal reason for conservative base available, improved condition assessment, re life evaluations, self-diagnosis, and even self-repa be fertile ground for innovations based on smart and systems Control of Power-Plant Cycle Chemistry and Atmospheric Emissions The health of water-touched and steam-touche nents in fossil-fueled or nuclear-fueled power p pends critically on the purity of process fluids solved oxygen, chloride ions, and a host of other im must be controlled at parts-per-billion levels, w tremendous challenge, since a large steam genera lates millions of kilograms (pounds) of water and s hour Opportunities for impurity ingress, corrosio position are pervasive, as shown in Fig 10 for drum boiler cycle Rapid response to cycle-chem sets is crucial Penalties for exceeding well-establi its on contaminants are severe: boiler tube failu lized corrosion, cracked steam-turbine disks an and increased erosion of turbine components by o ticles spalled from steam-touched tubes and pipe these ills can cause forced outages of substantial Clear needs exist for smart systems to address lenge: distributed on-line chemical sensors capab tioning in high-temperature water and steam, in chemicals to counter pollutants or chemical im and processors to coordinate multifunctional sen actuators Similarly, there are sizable financial and env tal benefits from reducing pollutant releases to th phere Various configurations of sensors, proces actuators can be envisaged; an ideal system wou pable of analyzing fuel as it enters a combustor, the combustion conditions in real time to minimi tion of pollutant species, and selectively activatin devices that extract residual pollutants from the Such systems would also calculate the effects of op changes on equipment life and on overall unit per and efficiency Systems Issues in Resonance Control One particularly insidious form of vibration in rot chinery is that caused by subsynchronous resonan which results from a match between the natural cies of mechanical components in a generating mechanisms that frustrate conventional NDE methods Overdesign of structures to resist hypothetical “worst-case” loads 2 Integrity of civil structures, especially concrete dams 2 Vibration of rotating machinery, leading to lower efficiencies and premature failure 1 Efficiency of blades in steam turbines and wind turbines 2 Monitoring and controlling impurity levels in water and steam 2 Optimizing combustion and control of emissions 1 Noise abatement in power plants and substations 3 Protection of dams and nuclear plants during seismic events 2 on-line analysis to locate damage and warn of incipient failure, as appropriate Eventually, develop systems that release neutralizing chemicals at damage sites Detect onset of unusual loads and deploy auxiliary members that supplement load-bearing capability Determine state of cure and structural defects in fresh concrete; monitor loads and structural responses throughout life; actuate mitigation and repair strategies, e.g., “smart” concrete r Active vibration-control methods from aerospace practice to suppress vibration in individual machines r Systems issues, e.g., subsynchronous resonance, requires new technologies to detect onset and actuate adjustments to transmission system parameters “Smart wing,” “adaptive skins,” and/or individual helicopter-blade control technologies to change airfoil shapes as a function of operation regime Requires chemical sensors, stable in highpurity water/steam at high temperatures and pressures, to measure pH and dissolved species; processors for coordinating signals and decisionmaking; actuators for injecting appropriate reagents to maintain or restore proper cycle chemistry On-line analysis of fuel entering combustors (by x-ray fluorescence, neutron backscattering, etc.); high-temperature chemical sensors for combustion gases; real-time control of individual burners by integrating sensor signals and calculating combustion adjustments that balance heat rate minimization and stack-gas composition; actuate ammonia/urea injectors, as needed, to react with NOx r Main source of noise in power plants is ventilation of auxiliary motor drives; new suppression approach needed r Noise cancellation by secondary acoustic technology for transformer hum Flexible connections with smart dampers and selectively augment structures with smart tendons Long-term Near-term to m Near-term Long-term Long-term Mid- to long-te Long-term Long-term Near-term Vision buried hazardous-waste tanks Buckling of structural members loaded in compression Cavitation erosion in pumps and hydroturbines 4 3 from aerospace sector Smart sensors detect incipient buckling; lateral stabilization then provided by piezoelectric actuators r Concepts from “smart wing” and “adaptive skins” technologies to effect dynamic changes in surface profiles of hydraulic machinery, thus preventing cavity formation by altering flow patterns in real time r Implement erosion-resistant claddings with shape-memory alloys Long-term Long-term Near-term Power Delivery Deterioration of underground cable 1 Real temperatures of highvoltage transmission lines 2 Condition assessment of transformers, especially life expenditures associated with temperature excursions and partial discharges 1 Condition assessment of wood poles 3 Multipurpose fiber-optic sensors could probably be adapted to detect and discriminate among void formation, water treeing, and corrosion of neutrals, i.e., selfdiagnosis Approaches for self-repair are unknown, although aspects of “smart concrete” (release of chemicals) could apply Operating limits based on thermal capacity are determined by computer models incorporating air temperature, wind velocity, incident sunlight, etc Knowledge about actual thermal conditions could result in up to 15% higher loading The requisite fiber-optic technology already exists; embedding fiber optics in overhead conductors is the next step Temperature monitoring by distributed, all-silica fiber optics based on Raman backscattering if spatial resolution can be improved to ≤0.1 m (4 in); monitoring oil composition with chemical sensors that measure moisture and acidity; partial discharge monitoring with combined ultrasonic (piezoelectric) and radio-frequency sensors Although they degrade by reaction with their surroundings, there is no generally accepted method for evaluating wood poles in service Vibration signature analysis is a likely approach Long-term to v Near- to midter Mid- to long-ter Midterm include damping with vertical shape-memory alloy members between suspended conductors or with SMA springs in the tower supports Shielding against electromagnetic fields a ? Vision Problem size scale: 1 Extremely important, widespread throughout industry, costly for each occurrence, or a majority safety concern 2 Very important, either widespread or very costly per occurrence; may be a major safety concern 3 Modestly important 4 Troublesome, but either relatively infrequent or not very costly per occurrence resonant electrical frequencies of the interconnected transmission system When these frequencies match, there is the possibility for uncontrolled interchange of energy and reinforcement of mechanical and electrical perturbations Where SSR has occurred it has resulted in unit-years of downtime (38) The power-transfer capability of transmission lines is limited by either thermal characteristics or by electrical stability characteristics of the system The stable powertransfer limit of transmission lines is given by P= (Vl )(Vs ) sin δ , χ where Vl and Vs are the load-end and source respectively, δ is the phase angle difference be two voltages, and χ is the reactance of the line reactance (χ ) can be reduced by installing seriescapacitors, and the transfer capability of the tra line is thereby increased Unfortunately, installi connected capacitors for compensation can creat trical resonance circuit and thus establish cond SSR SSR is a phenomenon so catastrophic that that might lead to its occurrence must be avoid ance starts with computer simulations that eva chance of SSR for all likely combinations of tra circuits and rotating machinery If there is a p HP turbine Feed IP turbine Attemperation LP turbine Condenser Makeup Deaerator Boiler HP heaters Condensate polisher Impurity ingress Corrosion Feed Deposition Figure 10 Major unit components and locations of impurity ingress, corrosion, and deposition in drum cycles (37) sensors on all key mechanical and transmission line components to detect incipient SSR, an intelligent processor to analyze signals and coordinate responses, and appropriate actuation of switchable parallel filters and series capacitors Temperatures of High-Voltage Transmission Lines One of the primary constraints on the amount of power that can be pushed down a transmission line is thermal capacity Operating limits are set by computer models that incorporate factors such as air temperature, wind velocity, incident sunlight, and a derating factor to ensure safe operation It has been estimated that 5% to 15% higher loading would be possible if actual thermal conditions were known on a continuous basis instead of relying on traditional loading guidelines (40) Transmission capacity is insufficient in several areas of the United States Significant benefit would accrue if more power could be transmitted without building new lines The size of the benefits is estimated as follows: A typical high voltage (345–765 kV) transmission line has a capacity of 1000 MW A 5% decrease in power equates to 50 MW If the line is thermally limited 20% of the time, the amount of power lost is 50,000 kW × 8760 h/yr × 0.2 = 87.5 × 106 kWh/yr At a wholesale price of $0.02/kWh, the increased revenue that would eventuate from knowing the actual temperature of a line is $1,750,000 per year Temperature measurement in real time is the first element of a smart system for which fiber optics seems admirably suited (41) Huston and Fuhr (42) cite several additional opportunities for the application of fiber-optic systems to electric power transmission lines: detecting overheating, detecting galloping, flaw detection in lines, and control of circuit breakers along a broken transmission line where electromagnetic interference might make conventional control systems inoperable Deterioration of Underground Cable There are now about one million miles of underground distribution lines in the United States, and there is growing pressure to put more of the distribution system underground This presents serious challenges to utilities, related mostly to difficulty of access for detecting damage or for repairing it As a consequence, cables are often operated until they fail, an undesirable situation that is becoming intolerable with increasing demand for electricity Cable materials, underground conditions, and system age are all factors in maintaining reliable service Cable is Figure 11 Typical construction of distribution-lin typically composed of phase conductors embedde centric insulation (usually a polymer such as poly that is surrounded by return ground conductors tral, usually copper), as shown in Fig 11 The s of cable insulation to temperature was discusse knowledge of actual temperatures along a cable tributed fiber-optic sensor allowed power transfe the cable to be optimized Thermal conditions ar only threat to cable integrity, however Undergro ditions almost always involve the presence of prolonged exposure to which causes insulation br by void formation and “water treeing” or corros copper neutral Water treeing is the developmen semiconductive paths that are believed to ori particles or voids Tree growth proceeds by pa charges and ionization at these electrical stres trations When a tree extends between two cond different potentials, the conductivity of the tree increases rapidly and culminates in a catastrop (43) These problems are widespread, detection is and repair practices are unwieldy Repair gene sists of injecting pressurized silicone into the die an attempt to drive out water Routes to solution obvious, but the benefits of self-analysis, and esp self-repair, would be substantial for either the die the neutral BIBLIOGRAPHY 1 Electric Power Trends Arthur Anderson & Co and C Energy Research Associates, Cambridge MA, 1992 2 Statistical Yearbook of the Electric Utility 1989, Edison Electric Institute, Washington, DC, 1 3 J.C Brown, P Dahl, and J Sparkman Rura Sourcebook, National Rural Electric Cooperative A Washington, DC, 1990 4 R Sachdeva In T Grandke and W.H Ko, eds., Senso prehensive Survey, Vol 1: Fundamentals and Gener VCH Publishers, New York, 1989, pp 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Acta 375: 17 7? ?18 5 (19 98) 11 7 R.W Coughlin, M Aizawa, and M Charles, Biote eng 18 : 19 9–208 (19 76) 11 8 A.L Margolin, V.A Izumrudov, V.K Svedas, and A Biotechnol Bioeng 24: 237–240 (19 82) 11 9 Y.E Kirsh,... behavior in materials can be derived from thermodynamic S1 S2 S3 S4 S5 S6 d 11 d 21 d = 31 d 41 d 51 d 61 D1 d12 d22 d32 d42 d52 d62 d13 d23 d33 d43 d53 d63 T T T ? ?11 ? ?12 ? ?13 T T T D2 = ε 21 ε22 ε23