Showing papers by "ABB Ltd published in 1989"

Implementation of a Lagrangian relaxation based unit commitment problem

Abstract: The unit commitment problem in a power system involves determining a start-up and shut-down schedule of units to be used to meet the forecasted demand, over a future short term (24-168 hour) period. In solving the unit commitment problem, generally two basic decisions are involved. The "unit commitment" decision involves determining which generating units are to be running during each hour of the planning horizon, considering system capacity requirements including reserve, and the constraints on the start up and shut down of units. The related "economic dispatch" decision involves the allocation of system demand and spinning reserve capacity among the operating units during each specific hour of operation. As these two decisions are interrelated, the unit commitment problem generally embraces both these decisions, and the objective is to obtain an overall least cost solution for operating the power system over the scheduling horizon. The unit commitment problem belongs to the class of complex combinatorial optimization problems. During the past decade a new approach named "Lagrangian Relaxation" has been evolving for generating efficient solutions for this class of problems. It derives its name from the well-known mathematical technique of using Lagrange multipliers for solving constrained optimization problems, but is really a decomposition technique for the solution of large scale mathematical programming problems. The Lagrangian relaxation methodology generates easy subproblems for deciding commitment and generation schedules for single units over the planning horizon, independent of the commitment of other units.

Collision broadening of two-dimensional excitons in a GaAs single quantum well

Abstract: The phase relaxation of two-dimensional (2D) heavy-hole excitons in a 12-nm GaAs single quantum well subjected to collisions with either free carriers or incoherent heavy-hole excitons is investigated by time-resolved degenerate four-wave mixing. The homogeneous linewidth corresponding to the phase coherence time reveals a collisional broadening due to exciton-exciton scattering and an 8 times stronger exciton-free carrier scattering. Both scattering processes are enhanced for 2D excitons as compared to 3D excitons.

The mechanism of leader breakdown in electronegative gases

Abstract: A survey is given of the present state of understanding of leader breakdown of electronegative gases in nonuniform field gaps and under fast-rising voltage waveforms. The basic physical processes involved are the formation of a pulsed streamer corona, the transformation of one of the streamers into a leader step, the temporal development of the leader channel, and the stepped propagation of the leader through the gap. The growth and structural characteristics of the corona are modeled and the results obtained are used to derive simple approximations for the spatial corona extension and the corona charge. Two leader inception mechanisms are discussed, namely, the stem and the precursor mechanisms. Inception criteria and characteristic time scales are derived for both of them in terms of the experimental parameters. A simplified model, which also predicts the random aspects of leader propagation through the gap, is presented. Some typical gas-insulation design problems are treated as examples. >

Prevention of transient voltage instabilities due to induction motor loads by static VAr compensators

Abstract: The application of static VAr compensators (SVC) to prevent transient voltage instability due to the presence of large induction loads at the terminals of long transmission lines is discussed. Eigenvalue analysis is used to identify the conditions for voltage instability. The analysis is supported by transient time simulations for the complete power system following large disturbances. It is found that SVC can obviate transient voltage instabilities and maintain the load voltage near its rated value. It is shown that replacing the SVC with mechanically switched capacitors may not provide stabilization owing to the time delays associated with voltage drop detection and breaker operation. >

Combustion chamber of a gas turbine and method of operating it

Abstract: In the combustion chamber of a gas turbine, an air distribution chamber (19) and a combustion space (7) are locationally separated from one another within the combustion chamber shell (1). A multiplicity of tubular elements (2) are located between the distibution chamber and the combustion space, in which elements a premixing and pre-evaporation of the fuel oil supplied via the premixing nozzles (15') and/or a premixing of the fuel gas supplied through the premixing nozzles (15") takes place with compressor air. Each tubular element (2) is provided with a flameholder (3) in the direction towards the combustion space (7). A diffusion nozzle (8) for fuel directed into the combustion space (7) is located within the flameholder. In operation on load, only a small part of the fuel supplied to each element (2) is burned by means of the diffusion nozzle (8), the major proportion, on the other hand, being burnt by means of the premixing nozzles (15' of 15").

Field-enhancing defects in polymeric insulators causing dielectric aging

Abstract: Defects that produce strong local field enhancement are discussed. They are especially harmful because they do not produce partial discharges detectable in usual factory control tests. Typical examples for such defects are electrode protrusions, floating conducting particles, and the tips of electrical trees. Charge injection from field enhancement tips is shown to be the first step in a series of pretreeing events. In model experiments using a needle/plate arrangement, a field threshold for injection is observed, separating a low-field regime of 'infinite' lifetime for the dielectric from a high-field regime where treeing will almost inevitably set in after some incubation time. This incubation time is shown to depend very sensitively on how much the applied voltage exceeds the value at which the critical field is reached locally. The value of this threshold field is in the range of megavolts per centimeter for pure or filled homogeneous insulators and about two orders of magnitude lower in compound insulators containing (bad) interfaces. >

Theoretical analysis of the current and energy flow to the anode in the diffuse vacuum arc

Abstract: The current energy flow to the anode in a diffuse vacuum arc is investigated using a simple multicathode-spot fluid description of the interelectrodic plasma. Decisive for the current constriction and the energy flow to the anode center is the space-charge sheath in front of the anode. This sheath not only determines the current-density distribution at the anode, but also may lead to a strong energy gain of the electrons before they reach the anode surface (in case the anode drop appears to be positive in the anode center). Numerical results are given and two possible scenarios for the transition from the diffuse to the anode-spot mode are discussed. >

Limiting-path model of the critical current in a textured YBa2Cu3O7- delta film.

Abstract: A limiting-path model for the determination of the critical current in a polycrystalline superconductor is presented which allows for the exact calculation of the critical current given the individual intergrain couplings. The model is used to determine the a-axis texturing dependence of the critical-current density in a c-axis--oriented polycrystalline ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ film. The critical-current density in untextured material is suppressed by a factor of \ensuremath{\simeq}(1/30 as compared to the single-crystal value and can be raised considerably only by strong a-axis texturing (to within 5\ifmmode^\circ\else\textdegree\fi{}). A nontrivial length dependence of the critical-current density is found for long polycrystalline wires.

Fiber-optic sensing of voltages by line integration of the electric field

Abstract: A fiber-optic sensor that is sensitive to the line integral of the electric field is presented. The sensor detects electric-potential differences by adding the scalar products of the local electric fields along the integration path times the path-segment vectors. This is achieved by exploiting symmetry properties of the converse piezoelectric effect. The sensor principle is experimentally demonstrated. Important performance parameters including integration accuracy, dynamic range, linearity, and bandwidth are examined.

Scale formation on the Ni-base superalloys IN 939 and IN 738 LC

Abstract: The scales formed on the superalloys IN 939 and IN 738 LC at 700, 900, and 1100°C in air have been investigated by optical, microprobe analysis and x-ray diffraction measurements. Both alloys form very similar scales. The main components are an outer TiO2 layer, an intermediate Cr2O3 layer with dissolved Ti, and an inner layer of (Ti, Nb, Ta)O2 with rutile structure. Beneath the scale an internal corrosion zone is formed that contained Al2O3 directly beneath the external scale and TiN further into the substrate.

Device for extending the performances of a radial compressor

Abstract: In a radial compressor the device for extending the performance at small throughputs by stabilizing the impeller flow in the inlet region comprises a recess (5) in the form of a groove which is oriented in the circumferential direction of the inlet duct (6) of the compressor, whereas in the flow direction it extends with a given axial width to the impeller (2). A stabilization ring (3) is integrated into said recess (5), being arranged in front of the impeller (2) and outside the principal flow (7) of the transported medium. A plurality of blades (4,4a), which are placed on the outer circumference of the stabilization ring (3), are in turn anchored to the inner contour of the recess (5).

Fault current limiter

Abstract: A current limiter according to the invention has two resistors, the first one consisting of a thin layer of a material which may become superconducting and the second one is a resistance layer applied on first resistor, the latter resistor layer being dimensioned such that its resistance becomes considerably lower than the resistance of the superconducting layer when it is not superconducting, however with a resistance of such a magnitude that, in the current circuit in question, it limits the current to a permissible value. For mechanical support of the resistors, an insulator is included in the current limiter, and the superconducting material is applied on insulator. The resistors and the insulator are arranged immersed into a cryotank.

Method and a device for fault location in the event of a fault on a power transmission line

Abstract: A device for determining the location of a fault at a fault position (F) on a power transmission line between two stations (P, Q), and in which the power transmission line has an unknown conduction impedance (Z PQ ), wherein, at one of the stations (P), capacitive voltage measuring transformers measure the phase voltage (U PM ) and the phase currents (I P ) or changes in the phase currents (ΔI P ) are measured on the occurrence of a fault. The phase voltage, phase currents or changes in the phase currents are low pass filtered; and the filtered phase voltage, phase currents or the change in the phase currents are converted from an analog to instantaneous digitized phase voltage, phase currents or changes in phase current values, respectively. The fault distance α and a value of an apparent fault resistance R F at the fault location are calculated, using linear regression, on the basis of the relationship: U.sub.PM =αZ.sub.PQ I.sub.P +R.sub.F I.sub.P +ΔU.sub.CVT ; where α represents a measure of the fault position, U F represents a voltage across the fault position and ΔU CVT represents a fault voltage introduced by said capacitive voltage measuring means. The fault distance is compared with an upper (α max ) and a lower (α min ) limit value and the apparent fault resistance is compared with an upper (R Fmax ) and a lower (R Fmin ) limit value. A tripping signal is generated when the fault position and the apparent fault resistance, respectively, are within the aforesaid limit values.

Metal Deposition with Incoherent Excimer Radiation

Abstract: VUV light-induced decomposition of palladium acetate films was performed by using a new incoherent excimer source. With pure xenon this excimer source emits radiation peaking at a wavelength of 172 nm. We investigated mainly the palladium deposition from spin-on palladium acetate films on aluminum oxide substrates. By using EMP we determined the palladium thickness as a function of UV intensity and exposure time. A remarkable temperature effect of the photolytic deposition process was observed also in a temperature range in which no thermal decomposition is possible. The exposure of spin-on palladium acetate films on ceramic substrates was also accomplished through metal contact masks. Patterned palladium films were reinforced by electroless copper and nickel plating processes [1]. The obtained structures had the same high edge quality as those produced by using excimer lasers [2].

Internal combustion engine with two-stage exhaust turbocharger and power output turbine

Abstract: In an internal combustion engine (1) with two-stage exhaust turbocharger (7 and 16; 9 and 11) and power output turbine (20), which can be coupled to the engine crankshaft (2) and driven by a portion of the engine exhaust gases, the outlet of the power output turbine (20) can be conductively connected by way of an exhaust gas recirculation line (28) to the inlet of the low pressure turbine (9) and the outlet of the high pressure compressor (16) can be connected to the high pressure exhaust line (5) upstream of the high pressure turbine (7) by way of a bypass line (36) in order to improve the partial load performance of the engine (1). The inflows of exhaust gas to the low pressure turbine (9) and of high pressure charge air to the high pressure turbine (7) by way of the exhaust gas lines (21, 28) and the bypass line (36) respectively are shut off or released by shut-off elements (22, 29, 37), which can be automatically controlled by known means as a function of the operating condition of the engine (1).

Uv Excimer Laser-Induced Deposition of Palladium from Palladium Acetate Films

Abstract: UV excimer laser-induced deposition of palladium from spin coated palladium acetate films in air is described. We have investigated mainly the deposition of palladium on aluminum oxide and quartz substrates and its dependence on the fluence and the number of excimer laser pulses. The decomposition mechanism was studied by measuring in situ the transmitted pulse energy during the exposure process. We have found that the excimer laser-induced decomposition of palladium acetate films is mainly pyrolytic and a simple model can be used to describe the decomposition process.

High voltage insulation system for electric machines

Abstract: In an insulating system for high-voltage machines, a three-layer insulating tape is proposed as turn-to-turn insulation which comprises a center mica layer (1) which is covered on both sides by plastic foils (2,3) having different thickness. Thermoplastic adhesive layers (4,5) on the outer surfaces of the foils (2,3) produce an intimate bonding of the turn-to-turn insulation to the conductor elements and to the main insulation. An insulation of such construction is distinguished by a high electrical life at increased temperature and a high surge withstand capability.

Method and apparatus for inspecting laminated iron core stacks for interlamination shorts

Abstract: In order to detect interlamination shorts (8 ) in the case of laminated core stacks, the core stack (1) is magnetized with an auxiliary winding The iron surface (15) is scanned with a measuring coil arrangement (5) comprising two electrically separated, mechanically interlinked coils (6, 7) The output signals from the coils are compared with each other in a downstream measuring instrument (9); in the case of an interlamination short, the fault current through the short-circuited laminations will induce in the coils different, phase-shifted voltages which make it possible to infer the position and size of the interlamination shorts

Method for preparing a ceramic suspension

Abstract: A method for preparing a ceramic suspension using alpha-Al2 O3 powder containing agglomerated powder particles includes dissolving ionic or polymeric reagents as additional dispersing agents in water or an organic solvent as a dispersion medium. Alpha-Al2 O3 powder is added thereto while being stirred. Ceramic molded articles may be produced from the suspension.

Method of cut position determination for printing machines

Abstract: A method of cut position determination for printing machines, wherein in order to ensure a synchronous running of the paper webs (P1-P4) to be folded and cut into newspapers (16) on a printing machine for rotary offset printing or rotary letter press printing, main and secondary registers (5, 7) are controlled in their position by means of servomotors (M1-M4) as a function of actuating signals (S M1 -S M4 ). Above each former-introduction guide roller (10), 4 photocells (11) are arranged equally spaced next to one another, which detect brightness signals (H A1 -H D4 ) from the printed surface of these paper webs at a scanning frequency of 20 khz. These brightness signals are subjected to a Fourier analysis in a microprocessor. The fundamental oscillation is evaluated, the fundamental oscillation with the greatest amplitude being selected from the 4 fundamental oscillations of each paper web. The phase position signal associated with the selected fundamental oscillation is used for calculation of one of the actuating signals (S M1 -S M4 ). Consequently, the cut position of the paper webs (P1-P4) can be determined without socalled register marks or register-keeping marks made on them.

Method and apparatus for monitoring the execution time of a computer program

Abstract: A method and apparatus are provided for observing the progress in time of an object program executed by a computer system. Information items relating to the flow of the object program are detected by an observation tool at an interface of the computer system being evaluated. Unambiguously identifiable observation points in the form of output commands are inserted at specifically selected points in a source program allocated to the object program. The observation points are stored in a table in a database in the observation tool. When the source program is executed, identification signals associated with the observation points are sent to the observation tool by the computer system. The observation tool calculates object program events which specify object program execution times for each object computer of the computer system. The calculated events are evaluated in the observation tool in the program language of the source program with reference to the observation points stored in table form.

Three-dimensional antiferromagnetic ordering in the light rare-earth high-T c superconductor NdBa2Cu3O6.86

Abstract: Powder neutron diffraction investigations performed in the temperature range from 20 mK to 300K prove that the magnetic Nd moments of the superconductor NdBa2Cu3O6.86 withTc=88 K order three-dimensionally (3D) antiferromagnetic belowTN=(551±10) mK. As in similar Gd and Dy compounds the corresponding wave vector isk=[1/2, 1/2, 1/2]. In approximate agreement with crystal field calculations the ordered magnetic moment of Nd amounts at saturation to (1.14±0.06) μB and at 25 mK the magnetic moments are oriented parallel [0,0,1]. The transition to the magnetically ordered state corresponds to the Landau type critical exponent β≈0.5, in contrast to the predominant 2D character of such heavy rare-earth systems. The crystal structure of NdBa2Cu3O6.86 is orthorhombic similar to the one of YBa2Cu3O7−x.

Filter equipment for power lines

Abstract: Filter equipment for power lines has a double-tuned shunt filter (F1) which has a series resonance circuit (C1, L1) connected in series with a parallel resonance circuit (C2, L2). The capacitor banks of the two resonance circuits are formed so as to have opposite signs on the temperature coefficent of the capacitor capacitance.

Ozone production in oxygen by means of F2-laser irradiation at λ=157.6 nm

Abstract: Ozone is generated in pure oxygen (p≦5 kPa), synthetic air (p≦7 kPa) and oxygen-argon mixtures (p≦3 kPa) by irradiation of these gases with the VUV light of a repetitively pulsed (f L≦15 Hz) F2-laser at λ=1576 nm with maximum about 4 mJ/pulse An absorption photometer measurement operating at 2537 nm (Hg line) determines the ozone concentration as a function of oxygen and/or additive gas pressure, the repetition frequency of the laser and the wall temperature of the reaction chamber The temporal development of the ozone concentration as a function of these parameters is calculated by means of rate equations for the species O(3 P), O2(X 3∑ g − ), O3(1 A 1), O(1 D), O2(a 1Δg), O2(b 1∑ g + ) and vibrationally excited O 3 * (1 A 1) and the photon distribution The maximum concentration of O3 in the sealed-off chamber reaches 16% in pure O2, 41% in air and 12% in a 1:5 O2-Ar mixture at 3 kPa The annihilation of O3 by the wall and temperature dependent volume processes (300 K≦T≦395 K) is studied and the experimental and theoretical results are compared

Method of identifying a user of a smart card

Abstract: A user (7) of a smart card (3) is considered to be identified if an identification code (PIN) of the user (7) agrees with an identification code (PIN) of the smart card (3). The smart card (3) is connected to a terminal (1). The smart card (3) generates at least one random number (Z), and informs the user (7) of it, using a display (4) on the card itself. The user keys in, via the terminal (1), a random code (K), which is the result of a combination of the user's identification code (PIN) and the at least one random number (Z). The combination is preferably addition or subtraction.

Crystal field in RBa2Cu3O7 (R rare earth) determined by neutron spectroscopy

Abstract: The crystal-field interaction of the high- T c superconductors RBa 2 Cu 3 O 7−δ (R  Nd, Dy, Ho) was determined by neutron spectroscopy. Here we summarize our results obtained for NdBa 2 Cu 3 O 7−δ . The observed energy spectra are strongly influenced by the oxygen vacancy concentration δ, and the quasielastic line width exhibits a sudden drop at T c .