A new lineup of general-purpose variable-frequency asynchronous motors developed by public corporation “NIPTIEM”

The basic results of the development of basic parts of a new lineup of asynchronous electric drives designed for operation within a variable-frequency electric drive are given. Their key differences from general-purpose commercial electric motors are shown.     

Application of wavelet analysis to the determination of partial discharge location in multiple-α transformer windings

The inner insulation system is a critical component of a power transformer. Its degradation may cause the device to fail while in service. If deterioration of the insulation system caused by Partial Discharge (PD) activity can be detected at an early stage, preventive maintenance measures can be taken. Due to the complex structure of power transformers, accurate locating of PD is not an easy task and is one of the main challenges in front of power utilities. Locating PD is more difficult in transformers with multiple-α windings. This problem comes to be vital in open access systems. A method for locating partial discharge within multiple-α windings is proposed, which is based on structural data of a transformer. A 66 kV/25 MVA transformer with fully interleaved winding and connected tap winding is used as test object. Wavelet transform is employed to process the partial discharge signals. Wavelet transform analysis method is a powerful tool for processing transients and non-stationary or time varying signals. Since the wavelet transform provides multi-scale analysis and time–frequency domain localization, it is particularly suitable to process the partial discharge signals. In order to improve the accuracy of the partial discharge location, a new technique for extracting Partial Discharge signals is introduced. Applying wavelet transform to a signal produces a wavelet detail coefficient distribution throughout the time-scale, which depends on the mother wavelet chosen. This technique is based on the capability of the chosen mother wavelet for generating coefficients with maximum values. The wavelet based de-noising method proposed in this paper can be successfully employed to extract PD pulse from the measured signal. It can provide enhanced information and further infer the original site of the PD pulse through capacitive ratio method. The method is described in details and the applications to determine the partial discharge location in multiple-α windings are explored.     

Optimization of gallium-doped ZnO thin films grown using Grey–Taguchi technique

In this paper, optimization of the process parameters considering multiple performance characteristics to prepare the transparent conducting gallium-doped zinc oxide thin films with radio frequency (RF) magnetron sputtering was investigated. Experiments based on the Grey–Taguchi technique were conducted to examine the effect of deposition parameters including RF power, process pressure, substrates temperature and process time, aiming to obtain highly transparent and conductive films. Comparing with the optimal parameter set selected from orthogonal array by Taguchi method, the optimal grey theory prediction design (GTPD) can receive an improvement of 5.75?% in electrical resistivity and 1.47?% in optical transmittance. Further refinements respectively to RF power and process pressure with fixing other parameters level in GTPD were explored. The results show the alteration on RF power and process pressure in the GTPD can receive over 31?% and 51?% of improvement in electrical resistivity, respectively, with keeping the visible range optical transmittance over?85?%.     

Use of mass loading to operate a thin film ultrasonic transducer in the 300 kHz–10 MHz frequency range

Thin film ultrasonic transducers have been designed which operate over an important frequency range, 300 kHz to 10 MHz. The transducers were made using piezoelectric aluminium nitride films a few microns thick. The films would have a fundamental thickness mode resonance at 1–3 GHz if fabricated as an unsupported film, however operation at much lower frequencies has been demonstrated when the transducers are fabricated on bulk substrates. This would enables them to be used in ultrasonic non-destructive testing in circumstances where the film can be deposited directly onto the object under test. We have found that the major factors influencing the below-resonance operation of the thin film transducers are the device impedance, the spectrum of the excitation pulse, and any mechanical (mass) loading applied to the back face of the transducer. Results are presented showing that the evolution of device impedance as a function of device area could be predicted using a PSpice model of the thin film transducer. The ability of the transducer to generate longitudinal mode pulses rather than shear wave pulses was found to depend on increasing the mechanical loading at the back face of the transducer. This mechanism for pulse generation was confirmed by Finite Element Modelling using PZFlex.     

Effect of sintering temperature on microstructure and piezoelectric properties of Pb-free BiFeO3–BaTiO3 ceramics in the composition range of large BiFeO3 concentrations

Lead-free (1-x)BiFeO₃–xBaTiO₃ [(1-x)BF-xBT] piezoelectric ceramics in the range of large BF concentrations were prepared by conventional oxide-mixed method at various sintering temperatures. The sintering temperatures have a significant effect on the microstructure of the ceramics, and the composition has a remarkable effect on optimal sintering temperature of the ceramics, which are closely related with piezoelectric properties. The grain size increased with increasing sintering temperature and the optimal sintering temperature increased with increasing BT content. The ceramics with x?=?0.275 sintered at 990 °C exhibit enhanced electrical properties of d ₃₃?=?136pC/N and k _p?=?0.312 due to the polarization rotation mechanisms at MPB and desired microstructure. These results show that the ceramic with x?=?0.275 is a promising lead-free high-temperature piezoelectric material.     

Determination of characteristics of erosion wear of grade 15Kh11MF steel with the Cr–CrC ion-plasma sprayed coating

Results of investigations of the influence of a Cr–CrC ion-plasma sprayed protective coating on characteristics and the intensity of erosion wear of grade 15Kh11MF steel at a gas–abrasive flow incidence angle of 30° and an experimental specimen (target) surface temperature of 550°С are presented. The Cr–CrC ion-plasma sprayed coating was formed in a Gefest vacuum installation by magnetron deposition. Investigations of the formed coating were carried out using a research and experimental facility complex that provided the study of the composition and structure of the coating, measurement of its thickness, roughness, microhardness, and determination of its relative resistance at the combined action of the gas–abrasive flow and high temperatures. The Cr–CrC coating with a thickness of 6.5 ± 0.3 μm has a finegrained structure with grains with dimensions of 20–40 nm and contains layers of chromium and chromium carbide. The main coating element is chromium. Its content in carbide layers is 89.4–91.9% at a carbon content of 6.8–9.5%. The coating microhardness is H_0.05 = 1350 ± 50 HV. The maximum wear of the 15Kh11MF steel target is observed at the angle of the gas–abrasive flow incidence that is close to 30° (30 7°). With this incidence angle and a target surface temperature of 550°С, the Cr–CrC coating extends the term to the surface failure and the appearance of a clear abrasive trace no less than four times. The coating failure has a local character, i.e., the target surface forms islands with the coating, between which the intensive wear of the base material occurs.     

Design Criteria for the Optimization of Series Inductors in AC?DC Thyristor Converters

An analysis is made of the functions of the series inductances in the ac-dc thyristor converting units, and the results of a theoretical study of their rating criteria are summarized. Such work was made as part of the recent redesign of ac-dc converters.     

Optimization of optical absorption coefficient in double modified Pöschl–Teller quantum wells

In this work, the intersubband optical absorption coefficient in double quantum wells (QWs) represented by a modified Pöschl–Teller confining potential is optimized. This potential is well suited for such purposes as it can easily become asymmetrical by a correct choice of its parameters set. By using the particle swarm optimization algorithm and numerical solution of the Schrödinger equation, accompanied with the perturbation theory, we found the optimal structure that the optical absorption coefficient is maximum. Applying this algorithm to double modified Pöschl–Teller QWs structure shows that the total optical absorption coefficient for this structure is \(1.22\times 10^6\, \hbox {m}^{-1}\) . Then, the refractive index changes is investigated by using the density matrix method.     

Short term load forecasting using wavelet transform combined with Holt–Winters and weighted nearest neighbor models

Short term load forecasting (STLF) is an integral part of power system operations as it is essential for ensuring supply of electrical energy with minimum expenses. This paper proposes a hybrid method based on wavelet transform, Triple Exponential Smoothing (TES) model and weighted nearest neighbor (WNN) model for STLF. The original demand series is decomposed, thresholded and reconstructed into deterministic and fluctuation series using Haar wavelet filters. The deterministic series that reflects the slow dynamics of load data is modeled using TES model while the fluctuation series that reflects the faster dynamics is fitted by WNN model. The forecasts of two subseries are composed to obtain the 24 h ahead load forecast. The performance of the proposed model is evaluated by applying it to forecast the day ahead load in the electricity markets of California and Spain. The results obtained demonstrate the forecast accuracy of the proposed technique.     

On the local approximation of the electron–photon interaction self-energy

We investigate the impact of the so-called local, i.e., diagonal, approximation for the electron–photon scattering self-energy, within the nonequilibrium Green’s function formalism. We report on three different systems to show that the local approximation may dramatically degrade expected selection rules, but that this degradation has minor impacts on the physical properties of realistic systems in which other scattering processes are assumed.     

Computational–Experimental Verification of Technologies of Utilization of the Concentrate Formed in the Reverse-Osmosis Water Demineralization Cycle

Technologies for utilizing the wastewater of the reverse-osmosis plants (ROPs) to prepare the make-up water for power-generating plants of combined heat and power plants and nuclear power plants are proposed and substantiated using mathematical models and full-scale experiments. The ROPs use natural feedwater with a wide range of quality characteristics. For the first time, variants of the treatment of the concentrate formed in the ROP cycle have been proposed for the reuse of the latter by acidifying it in H-type cation- exchange filters charged with a weakly acidic cation-exchange resin. By admixing part of the filtrate processed in the H-type cation-exchange filters to the feedwater, the latter is acidified thus reducing the probability of formation of carbonaceous sediments and water consumption. The rest of the filtrate subjected to a conversion process is used as a constituent of the make-up feedwater of the heating system or potable water, which eliminates the discharge of the reverse-osmosis plant wastewater into the environment. Another feature of the proposed technology is that the H-type cation-exchange filters are integrated into a regenerant solution reuse circuit (RSRC). As a result, the consumption rate of sulfuric acid for regeneration equals the stoichiometric rate and the regeneration yields gypsum used to produce a binding agent for construction. The kinetics of separation of gypsum from the spent regenerant solutions with different chemical compositions was studied experimentally as applied to the RSRC conditions. The procedure of operating filters charged with the Lewatit CNP-LF cation-exchange resin was trialed under production conditions. It was established that the height of the filtering cation-exchange resin layer should be 1.0–1.5 m and the concentration of the regenerant solution should not exceed 0.8% at a rate of 10–15 m/h. The basic components of the technological scheme were trialed under production conditions on a water treatment plant in service.     

Application of Hybrid Differential Evolution–Grey Wolf Optimization Algorithm for Automatic Generation Control of a Multi-Source Interconnected Power System Using Optimal Fuzzy–PID Controller

This paper deals with an optimal hybrid fuzzy-Proportional Integral Derivative (fuzzy-PID) controller optimized by hybrid differential evolution–Grey Wolf optimization algorithm for automatic generation control of an interconnected multi-source power system. Here a two area system is considered; each area is provided with three types of sources namely a thermal unit with reheat turbine, a hydro unit and a gas unit. The dynamic performance of the system is analyzed under two cases: with AC tie-line and with AC-DC tie-line. The efficiency and effectiveness of the proposed controller is substantiated equally in the two cases. The sturdiness of the system is proved by varying the values of the system parameters. The supremacy of the recommended work is additionally ascertained by comparison with the recently published results like differential evolution optimized PID Controller and hybrid Local Unimodal Sampling-Teaching Learning based Optimization (LUS-TLBO) optimized fuzzy-PID controller. The dynamic performance of the system is observed in terms of settling time, peak overshoot and peak undershoot. Finally the analysis is extended by applying the proposed control technique in two different models namely (i) A three area unequal thermal system considering proper generation rate constraints (GRC) and (ii) A three area hydro-thermal system with mechanical hydro governor. These test results reveal the adaptability of the proposed method in multi-area interconnected power system.     

Assessment of myocardial viability with MR—the Cologne perspective

4. Conclusion Despite the evaluation of different parameters of myocardial viability by PET, TEE and MRI, their positive and negative predictive accuracies are fairly comparable. Therefore, the choice of the method to date mainly depends on expertise and available resources. An accepted reference standard to assess the diagnostic accuracy of imaging techniques is the post-revascularization recovery of regional LV function. In this respect, dobutamine-MRI proved to be a reliable and clinically feasible approach in a head to head comparison with FDG-PET and dobutamine-TEE. However, there is still limited information with respect to the potential benefit of revascularization procedures in the clinically important subset of patients with viable myocardium, markedly reduced LV function and congestive heart failure. In this patient population, the advantageous features of MRI including high spatial and temporal resolution, three-dimensional capability with unlimited field of view and the capability to measure perfusion may increase the clinical impact of MRI compared to established imaging techniques. Moreover, improvement of global LV ejection fraction, alleviation of symptoms and survival are fundamental clinical end points to additionally evaluate the predictive value of MR-studies for clinical decision making in patients with left ventricular dysfunction and persisting viable myocardial tissue.     

Current and voltage based bit errors and their combined mitigation for the Kirchhoff-law–Johnson-noise secure key exchange

We classify and analyze bit errors in the current measurement mode of the Kirchhoff-law–Johnson-noise (KLJN) key distribution. The error probability decays exponentially with increasing bit exchange period and fixed bandwidth, which is similar to the error probability decay in the voltage measurement mode. We also analyze the combination of voltage and current modes for error removal. In this combination method, the error probability is still an exponential function that decays with the duration of the bit exchange period, but it has superior fidelity to the former schemes.     

Coupled circuit–field formulation for analysis of parallel operation of converters with interphase transformer

This paper deals with the coupled circuit–field analysis of an interphase transformer (IPT) required for two three-pulse controlled converters operating in parallel for the typical low voltage high current electrolysis application. Two-dimensional nonlinear transient finite element (FE) model of the IPT is coupled with external power electronic circuit comprised of switching thyristors. Output current is maintained constant at 6000 A by implementing current feedback control system. The resulting system of transient nonlinear equations is solved by backward Euler and Newton–Raphson methods, and analyzed under balanced, unbalanced and short circuit conditions. The results obtained from short circuit condition are verified with experimental results and design values, making them helpful for design purpose.