Improving of the Probing Signal’s Spectral Content for Devices Nuclear Magnetic Logging

The method of nuclear magnetic logging (NML) allows to distinguish easily enough the intervals in which there are hydrocarbons and to forecast their extraction. Moreover, the principles of measuring using this method are simple enough, despite the difficulties of processes. There were described method of improving spectral composition of probing voltage NML device in this article. The disadvantage of the method is that the resonance area covers all reservoir fluids. Therefore, search for a way to reduce the frequency spectrum and extend the range of the device of nuclear magnetic resonance is a rather urgent task. In the article is stated that within conducting researches is necessary probing signals of large capacity. In this case, it is more appropriate to use switch mode of the power converters. The system of multilevel inverter is created on the base of these converters that allows to get probing signal simply enough. A three-level inverter that generates high-frequency pulses is considered. A virtual model of the converter is constructed together with smoothing and resonant filters, which generate the probing voltage in nuclear magnetic resonance (NMR) devices, using a modified Carr-Purcell-Meiboom-Gill sequence. The result is a wide range of voltages with side harmonics, which have the significant influence on the output signal relative to the base frequency which the NMR device is tuned. The analysis of the harmonic composition of this voltage is conducted. Calculations of intermodulation distortion coefficients for the first and two side harmonics are given. To reduce the influence of side harmonics in the output signal on the quality of measurement by NMR devices, it is proposed to implement additional generators with the phase difference between the side harmonic and the initial phase will be a half of period. The inductors used are transformers that have a ratio of primary and secondary windings of 1: 1 and the secondary winding has the same value of inductance as the replaced coil that was in the model without modifications. Anti-phase side harmonic generators are connected to the primary windings. In this way additionally implemented a galvanic isolation between the generator and the main signal. As a result of simulation of such a converter is obtained an alternative spectral composition of the output signal. After calculations and comparison of the obtained coefficients, it is shown that the proposed method really improves the spectral composition of the output signal. The disadvantages of using this method of spectrum improvement are considered as well. The relative voltage improvement in the case of a 30 ohms load is calculated. The simulation results of the proposed method show an improvement in the spectral composition of the probing voltage by ~ 2.68 times. With this method, it is possible to dampen unwanted side harmonics by adjusting the appropriate frequencies and initial phases so that the generator is always running in antiphase.

Rectifilter for electric arc plasma plant

This article presents the results of the development and research of a new type of AC-DC converter - a filter-rectifier (or rectifilter). The object of application of the proposed device is an industrial plant of electric arc plasma processing, the operation of which requires maintaining a constant value of the arc current and is accompanied by a high level of harmonic distortion and consumed reactive energy. From the point of view of the reactive power compensation and harmonic filtering strategy, the rectifilter can be attributed to active electric power filters and FACTS, however, from the position of the main function performed, it is a direct current source, an AC to DC converter, an active rectifier. This work describes in detail the principles of operation of the control system and the hardware architecture of the device. Mathematical modeling of the rectifilter and analysis of the graphs of the consumed alternating current, rectified current, analysis of the harmonic composition and power factor in comparison with the thyristor rectifier of an electric arc plasmatron were carried out.

Experimental study of the control of operating modes of a plate feeder based on the frequency-controlled electric drive

An experimental study of the control of the operating modes of the plate feeder based on a frequency-controlled electric drive in the mining industry has been carried out. The graphs of measurements of the electrical parameters of the electric drive supplied from the frequency converter of the plastic feeder, instantaneous values of harmonic composition of voltage and current up to 50 harmonics, as well as changes in current and voltage harmonics over a period of 30 minutes were obtained. Measurement of oscillograms of voltage and current of each phase in operating mode and the moment of turning off and turning on the electric motor of the plastic feeder. The issues of control of starting modes of the plate feeder from frequency-controlled electric drives are considered. It has been determined that frequency start-up with the linear control law for the frequency of the plate feeder as a function of time and technological parameters are the most acceptable condition for starting modes.

Experimental studies of the effect of a hybrid inverter on power quality

The integration of alternative energy sources and various technologies of distributed generation with power electronic converters in electrical networks leads to an increase in the diversity of the network, but at the same time to the tightening of the requirements of various standards, for exam-ple, a limited harmonic composition of the generated current, continuous operation of the device with voltage distortion, etc. Taking this fact into account, the paper presents the results of experi-mental studies of the effect of a hybrid inverter on power quality indicators at the point of common connection. A laboratory bench was developed. It consists of a three-phase hybrid inverter, a stor-age battery, a linear load in the form of an active resistance and a capacitor unit. The inverter has been connected to the power supply for parallel operation to supply the load in the form of active resistance. The modes of battery charging and power delivery to the network with two variations of the system resistance were investigated. The power output from the inverter varied from 500 W to 2 kW in the mode of generating electricity to the grid, and in the range from 50 to 300 W in the bat-tery charging mode. As a result of laboratory studies, the dependences of the total harmonic current distortion (THDI) were obtained for various operating modes of the inverter and system resistances. On the basis of the obtained results, an algorithm for the selection of methods and means to ensure electromagnetic compatibility during operation of the load and a hybrid inverter with energy storage was developed. It makes it possible to reduce the effect of hybrid inverters on the voltage distortion of the supply network.

Application of Multilevel Voltage Inverters in Distributed Series Compensation Devices

The operation principles of multilevel inverter circuits and methods for controlling them are considered. The operation of a multilevel circuit as part of a distributed transformer-based series compensation device is analyzed. The specific feature pertinent to the operation of a self-excited inverter within a distributed series compensation device is that it is loaded on the transformer connected in series into the power transmission line. In this case, the load is in fact a current transformer. Analytical expressions for calculating the circuit parameters are presented. The results of spectral modeling and simulation of the multilevel circuit in different modes of its operation are given. By using the spectral modeling, the currents and voltages of all power circuit components and their harmonic composition were estimated in the steady-state operation mode, and it has been shown that inductive injection is the heaviest mode of operation, because the inverter current reaches its maximum value in this mode. In using the multilevel circuit, additional requirements are posed to the control system, which, in addition to ensuring stable control of the output voltage, must also balance the voltages across the capacitors in the inverter arm. In selecting a storage capacitor and filter capacitor, it should be borne in mind that the maximum possible voltage across these components is determined not only by the necessary boost voltage, but also by the line current in the rectifier mode and can be significantly higher than the originally evaluated value. The obtained results can be used in designing distributed series compensation devices on the basis of an NPC inverter.

Morphometric properties of alternate bars and water discharge: a laboratory investigation

The formation of alternate bars in straightened river reaches represents a fundamental process of river morphodynamics that has received great attention in the last decades. It is well-established that migrating alternate bars arise from an autogenic instability mechanism occurring when the channel width-to-depth ratio is sufficiently large. While several empirical and theoretical relations are available for predicting how bar height and length depend on the key dimensionless parameters, there is a lack of direct, quantitative information about the dependence of bar properties on flow discharge. We performed a series of experiments in a long, mobile-bed flume with fixed and straight banks at different discharges. The self-formed bed topography was surveyed, different metrics were analyzed to obtain quantitative information about bar height and shape, and results were interpreted in the light of existing theoretical models. The analysis reveals that the shape of alternate bars highly depends on their formative discharge, with remarkable variations in the harmonic composition and a strong decreasing trend of the skewness of the bed elevation. Similarly, the height of alternate bars clearly decreases with the water discharge, in quantitative agreement with theoretical predictions. However, the disappearance of bars when discharge exceeds a critical threshold is not as sharp as expected due to the formation of so-called “diagonal bars”. This work provides basic information for modeling and interpreting short-term morphological variations during individual flood events and long-term trajectories due to alterations of the hydrological regime.