Modifications of the DC Raytheon–Statz model for SiC MESFETs

In the paper the problem of modelling DC characteristics of SiC MESFETs is presented. Some modifications of the popular Raytheon–Statz model built‐in in SPICE are proposed. The original and the modified models are verified experimentally by comparison of the measured and simulated device characteristics. One of the two available today on the market SiC MESFETs–the transistor CRF24010 offered by Cree, Inc. is chosen for investigations. Copyright © 2008 John Wiley & Sons, Ltd.     

Estimation of Available Wave Energy in the Barents Sea

The purpose of this research is to estimate the energy potential of the Barents Sea based on numerical modeling of the wave energy over a long period of time from 1979 to 2010. Using the WaveWatchIII wave model, the wave energy flux in the open part and in the coastal zone of the Barents Sea has been calculated. The calculations are based on the data of the NCEP/CFSR reanalysis with spatial resolution of 0.3°. The calculations were performed on a unstructured grid, which has high spatial resolution at the shore (200–500 m). The long-term average annual significant wave height¹ varies from 1.5–2.0 m for the open part of the Barents Sea to 1.0–1.5 m in the coastal zone of Murmansk oblast. The long-term average annual wave energy flux varies from 15–20 kW/m for the open part of the Barents Sea to 5–10 kW/m in the coastal zone of Murmansk region. The probability of exceedance of wave energy of more than 1 kW/m is 80–90% for the open part of the sea and 70–75% at the northeastern coast of the Rybachy Peninsula. To the east and west of the peninsula, this figure decreases significantly. Near the village of Teriberka, the probability of exceedance of the wave energy is 65–70%. The probability of exceedance of energy of more than 5 kW/m is 50–60% in the open sea and it does not exceed 35% in the coastal zone. The average probability of exceedance of the wave energy is subject to seasonal fluctuations. Thus, in the coastal zone, the probability of exceedance of energy of 1 kW/m is approximately 90% in the winter months and it does not exceed 50% in summer. The obtained results can be applied to designing a wave power station in the Barents Sea.     

Comparison of several discretization methods of the Steklov–Poincaré operator

In this paper, we present three methods to discretize the Steklov–Poincaré operator. Two of these methods are already well known and commonly used and the third one is new. These methods are based either on the ballooning technique or on the integral theory or on the Calderon equations and we recall the principles of the discretization for each method. Then, we implement these discretization procedures in a code which treats the three‐dimensional magnetostatic problem with a mixed and hybrid finite element method. The exterior domain is treated with the Steklov–Poincaré operator discretized using the three procedures. A comparison in terms of precision, performance and ease of implementation is given. Copyright © 2006 John Wiley & Sons, Ltd.     

On the use of silicone liquids in power transformers

The insulation and basic physical characteristics of insulation liquids MIDEL 7131 (ester) and SOFEKSIL–TSZh (silicone liquid) are considered. It is shown that the SOFEKSIL–TSZh liquid is characterized by a higher flash point, which is important for providing the fire safety of high-voltage electrical equipment. Taking into account that contradictory data on the electrical strength of silicone liquids are contradictory, studies on the electric strength of the SOFEKSIL–TSZh liquid and transformer oil have been performed for sharply nonuniform fields at an impulse voltage of 1.2/50 μs for both polarities. It is shown that the electric strength of the SOFEKSIL–TSZh liquid is similar to the electric strength of GK transformer oil and MIDEL 7131 liquid. It is concluded that the SOFEKSIL–TSZh liquid can be used in power transformers in the case of increased requirements for fire safety.     

Modeling of a coil system considering frequency-dependent inductances and losses. Determination of the equivalent circuit impedances

A methodology for determining the equivalent circuit impedances of a system of magnetically coupled coils is presented in this paper. The structure of the equivalent circuit has been proposed in previous works [Mombello (2000) Electr Eng 84:3–10; 84:11–19]. Starting from of a series of impedance measurements on the coil system for an appropriate frequency range, the necessary information is acquired to begin a process of identification of the circuit parameters. The parameter identification procedure is detailed, and consists of two successive minimization processes. Fundamental requirementts for preserving the precision of the results, which are highly sensitive to small variations in the parameters, are given.     

Investigation of numerical time‐integrations of Maxwell's equations using the staggered grid spatial discretization

The Yee‐method is a simple and elegant way of solving the time‐dependent Maxwell's equations. On the other hand, this method has some inherent drawbacks too. The main one is that its stability requires a very strict upper bound for the possible time‐steps. This is why, during the last decade, the main goal was to construct such methods that are unconditionally stable. This means that the time‐step can be chosen based only on accuracy instead of stability considerations. In this paper we give a uniform treatment of methods that use the same spatial staggered grid approximation as the classical Yee‐method. Three other numerical methods are discussed: the Namiki–Zheng–Chen–Zhang alternating direction implicit method (NZCZ), the Kole–Figge‐de Raedt method (KFR) and a Krylov‐space method. All methods are discussed with non‐homogeneous material parameters. We show how the existing finite difference numerical methods are based on the approximation of a matrix exponential. With this formulation we prove the unconditional stability of the NZCZ method without any computer algebraic tool. Moreover, we accelerate the Krylov‐space method with a skew‐symmetric formulation of the semi‐discretized equations. Our main goal is to compare the methods from the point of view of the computational speed. This question is investigated in ID numerical tests. Copyright © 2005 John Wiley & Sons, Ltd.     

Moisture determination of the main insulation in a transformer by frequency‐domain spectroscopy

The presence of moisture in the oil–paper insulation in a transformer drastically accelerates the aging process of the insulation and reduces the service life of the transformer. To analyse the influence of moisture on the dielectric response of the oil–paper insulation and to precisely determine the moisture content of the transformer by frequency‐domain spectroscopy, the modified Cole–Cole model is introduced to fit the frequency versus dielectric responses of the oil–paper insulation samples with different moisture contents, and the influence of the variation in moisture content on the parameters in the modified Cole–Cole model is investigated. Results show that the modified Cole–Cole model parameters, including the α and β relaxation components as well as the DC and hopping conductivity components, can be used to effectively fit the frequency versus dielectric response curve of the oil–paper insulation. The characteristic parameters τ_α and τ_β in this model are found to be sensitive to changes in the moisture content. They can be used to quantitatively evaluate the moisture content in a transformer insulation system. A case study is presented to verify the effectiveness of the proposed technique in assessing the moisture content of onsite transformers. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Combustion of bark and wood waste in the fluidized bed boiler

In the Energy Development Strategy of Russia for the Period until 2035, special attention is paid to increased use of local fuel kinds—one of which is biofuel, in particular, bark and wood waste (BWW)— whose application at thermal power plants in Russia has been not developed due to the lack of appropriate technologies mastered by domestic energy mechanical engineering. The article describes the experience of BWW combustion in fluidized bed boilers installed on the energy objects of northern European countries. Based on this, reference points were defined (it is the section of boiler air-gas path where initially the approximate temperatures are set), making it possible to carry out a thermal design of a boiler and ensure its operation reliability. Permissible gas temperature at the furnace outlet at BWW combustion amounted to 950–1000°C. Exit gas temperature, depending on the implementation of special measures on protection of air heater from corrosion, amounted to 140–190°C. Recommended hot air temperature is within the range of 200–250°C. Recommendations for determining the boiler furnace dimensions are presented. Based on the presented reference temperatures in the main reference points, the thermal design of hot water boiler of KV-F-116-150 type with 116 MW capacity was carried out. The analysis of the results and comparison of designed boiler characteristics with operating energy boilers, in which a fuel is burned in a fluidized bed, were carried out. It is shown that, with increasing the boiler capacity, the ratio of its heating power Q to the crosssectional area of furnace chamber F rises. For power-generating boiler of thermal capacity of 100 MW, the ratio is within 1.8–2.2MW/m². The boiler efficiency exceeds 90% in the range of changes of exit gas temperature typical for such equipment.     

On the asymptotic behavior of the Durbin–Watson statistic for ARX processes in adaptive tracking

A wide literature is available on the asymptotic behavior of the Durbin–Watson statistic for autoregressive models. However, it is impossible to find results on the Durbin–Watson statistic for autoregressive models with adaptive control. Our purpose is to fill the gap by establishing the asymptotic behavior of the Durbin–Watson statistic for ARX models in adaptive tracking. On the one hand, we show the almost sure convergence as well as the asymptotic normality of the least squares estimators of the unknown parameters of the ARX models. On the other hand, we establish the almost sure convergence of the Durbin–Watson statistic and its asymptotic normality. Finally, we propose a bilateral statistical test for residual autocorrelation in adaptive tracking. Copyright © 2013 John Wiley & Sons, Ltd.     

Estimation of Efficiency of the Cooling Channel of the Nozzle Blade of Gas-Turbine Engines

The main direction of improvement of gas-turbine plants (GTP) and gas-turbine engines (GTE) is increasing the gas temperature at the turbine inlet. For the solution of this problem, promising systems of intensification of heat exchange in cooled turbine blades are developed. With this purpose, studies of the efficiency of the cooling channel of the nozzle blade in the basic modification and of the channel after constructive measures for improvement of the cooling system by the method of calorimetry in a liquid-metal thermostat were conducted. The combined system of heat-exchange intensification with the complicated scheme of branched channels is developed; it consists of a vortex matrix and three rows of inclined intermittent trip strips. The maximum value of hydraulic resistance ξ is observed at the first row of the trip strips, which is connected with the effect of dynamic impact of airflow on the channel walls, its turbulence, and rotation by 117° at the inlet to the channels formed by the trip strips. These factors explain the high value of hydraulic resistance equal to 3.7–3.4 for the first row of the trip strips. The obtained effect was also confirmed by the results of thermal tests, i.e., the unevenness of heat transfer on the back and on the trough of the blade is observed at the first row of the trip strips, which amounts 8–12%. This unevenness has a fading character; at the second row of the trip strips, it amounts to 3–7%, and it is almost absent at the third row. At the area of vortex matrix, the intensity of heat exchange on the blade back is higher as compared to the trough, which is explained by the different height of the matrix ribs on its opposite sides. The design changes in the nozzle blade of basic modification made it possible to increase the intensity of heat exchange by 20–50% in the area of the vortex matrix and by 15–30% on the section of inclined intermittent trip strips. As a result of research, new criteria dependences for the complicated systems of heat exchange intensification were obtained. The design of nozzle blades can be used when developing the promising high-temperature gas turbines.     

Calculating the caloric properties of dissociated steam at high temperatures

Lookup tables and the hs-diagram of the caloric parameters of dissociated steam are drawn up in the temperature and pressure ranges 1250–4000 K and 0.1–10 MPa for calculating the processes in thermal power installations that use dissociated steam as working fluid. Unlike the existing tables for thermophysical properties of dissociated steam, the enthalpy presented in the proposed tables has positive values in the entire range of the considered parameters. The enthalpy of mixture includes the entire energy spent in the chemical reaction of dissociation for breaking the bonds in steam molecules. The caloric parameters are determined from the reference temperature equal to 0°C adopted in the methods for calculating the parameters of nondissociated steam, due to which it becomes possible to carry out coordinated calculations of processes in thermal power installations. Supplements to the existing tables for calculating the above-mentioned caloric parameters are developed. Dissociated steam expansion processes are calculated for the conditions with and without recombination of dissociation products at the same values of initial parameters and final pressure. It has been determined that the change of enthalpy and the work done in the expansion process without recombination are smaller than they are in the process involving recombination of dissociation products. The error of the performed calculations of caloric parameters is less than 0.1%.     

Equations for calculating the properties of dissociated steam

The equations of state for dissociated steam have been developed in the temperature and pressure ranges of 1250–2300 K and 0.01–10.00 MPa for calculating thermodynamic processes in thermal power units operating on high-temperature steam. These equations are based on the property tables for dissociated steam derived at a reference temperature of 0 K. It is assumed that the initial substance is steam, the dissociation of which—in accordance with the most likely chemical reactions—results in formation of molecules of hydrogen, oxygen, steam, hydroxyl, and atoms of oxygen and hydrogen. Differential thermodynamic correlations, considering a change in the chemical potential and the composition of the mixture, during the steam dissociation are used. A reference temperature of 0.01°С used in the calculation of parameters of nondissociated steam has been adopted to predict processes in thermal power units without matching the reference temperatures and to account for transformation of dissociated steam into its usual form for which there is the international system of equations with the water triple point of 0.01°С taken as the reference. In the investigated region, the deviation of dissociated steam properties from those of nondissociated steam, which increases with decreasing the pressure or increasing the temperature, was determined. For a pressure of 0.02 MPa and a temperature of 2200 K, these deviations are 512 kJ/kg for the enthalpy, 0.2574 kJ/(kg K) for the entropy, and 3.431 kJ/(kg K) for the heat capacity at constant pressure. The maximum deviation of the dissociated steam properties calculated by the developed equations from the handbook values that these equations are based on does not exceed 0.03–0.05%.     

New theorems in the synthesis of passive multiplexers

Coupling networks that divide the frequency spectrum into separate frequency bands and also provide desired filtering are known as multiplexers. In this paper we present four new theorems concerning the synthesis-theoretic structure of lumped passive multiplexers constructed as lossless reciprocal n-ports. In particular we prove in Theorem 1 that any set of n – 1 admissible power gains, complementary or otherwise, can be realized by a series interconnection of n–1 appropriately chosen non-Foster positive-real functions. In Theorems 2–4 we establish various necessary and sufficient conditions for the realization of bounded-real gains s₂₁(p),…, s_n1(p) given both in magnitude and phase. These conditions reveal that the general problem is one of Nevalinna-Pick interpolation. Lastly, five worked examples are used to illustrate all facets of the theory.     

Efficient three‐dimensional parallel simulations of PHEMTs

An efficient 3D semiconductor device simulator is presented for a memory distributed multiprocessor environment using the drift–diffusion (D–D) approach for carrier transport. The current continuity equation and the Poisson equation, required to be solved iteratively in the D–D approach, are discretized using a finite element method (FEM) on an unstructured tetrahedral mesh. Parallel algorithms are employed to speed up the solution. The simulator has been applied to study a pseudomorphic high electron mobility transistor (PHEMT). We have carried out a careful calibration against experimental I–V characteristics of the 120 nm PHEMT achieving an excellent agreement. A simplification of the device buffer, which effectively reduces the mesh size, is investigated in order to speed up the simulations. The 3D device FEM simulator has achieved almost a linear parallel scalability for up to eight processors. Copyright © 2005 John Wiley & Sons, Ltd.     

An efficient algorithm for optimizing the electrical performance of HBTs

A physical model for AlGaAs/GaAs heterojunction bipolar transistor with different emitter and base structures is proposed. The recombination currents in various depletion regions of the device are derived and are used to calculate the collector current in the range of 300–600 K. The theoretical predictions of the model are compared with the numerical and experimental data available in the literature. The model is used to derive an efficient algorithm that optimizes the device structure for a given unity current gain frequency and collector current. Copyright © 2003 John Wiley & Sons, Ltd.     

Solar Heat Supply: World Statistics and Peculiarities of the Russian Experience

Summarized data on the number and types of solar collectors and solar plants in use in various countries of the world, as well as on the market development dynamics and specific thermal capacity of operating solar plants per 1000 people, are given. State demand stimulation activities for solar plants are presented for some countries. It is noted that the modern trend in the improvement of solar collectors is the price reduction for materials with the substitution of copper for aluminum in the absorber manufacturing and the reduction of the energy-output ratio using soldering, crimping, and adhesive joints instead of welding. The minimal cost of the generated heat energy is provided by centralized solar heat supply systems. The values of the area of solar plants in Russia (2017), their structure, the features of solar collectors, including Russian-made, are presented. It is indicated that constructions of solar collectors with the optimal cost-effectiveness ratio are in demand on the Russian market. The information on the state of development and use of solar heat plants in Russia is summarized. The main design decisions and operating features of large solar plants in Narimanov, Astrakhan oblast (4400 m²), and in Ust-Labinsk, Krasnodar krai (600 m²), have been considered. It is established that the prospects of the Russian market are determined by the solar radiation in regions as well as the costs of solar collectors and replaceable conventional energy carriers. With allowance for the existing trends and peculiarities of regional development, the prospective Russian solar power market is estimated at 1400000–1500000 m² (1100–1200 MW).     

Identifying the distribution difference between two populations of fuzzy data based on a nonparametric statistical method

Nonparametric statistical tests are a distribution‐free method without any assumption that data are drawn from a particular probability distribution. In this paper, to identify the distribution difference between two populations of fuzzy data, we derive a function that can describe continuous fuzzy data. In particular, the Kolmogorov–Smirnov two‐sample test is used for distinguishing two populations of fuzzy data. Empirical studies illustrate that the Kolmogorov–Smirnov two‐sample test enables us to judge whether two independent samples of continuous fuzzy data are derived from the same population. The results show that the proposed function is successful in distinguishing two populations of continuous fuzzy data and useful in various applications. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Optimal expansions of multivariable ARX processes on Laguerre bases via the Newton–Raphson method

In this article, an optimal linear MIMO system approximation by using discrete‐time MIMO autoregressive with exogenous input (ARX) model is proposed. Each polynomial function of the MIMO ARX model associated with the inputs and with the outputs is expanded on independent Laguerre orthonormal basis. The resulting model is entitled MIMO ARX–Laguerre model. The optimal approximation of which is ensured once the poles characterizing each Laguerre orthonormal basis are set to their optimal values. In this paper, a new method to estimate, from input/output measurements, the optimal Laguerre poles of the MIMO ARX–Laguerre model is proposed. The method consists in applying the Newton–Raphson's iterative technique in which the gradient and the Hessian are expressed analytically. The proposed algorithm is tested on a numerical example and on a benchmark system. Simulation results show the effectiveness of the proposed optimal modeling method. Copyright © 2015 John Wiley & Sons, Ltd.