Showing papers by "Ivanovo State Power University published in 2019"

Development and study of a dynamic model of single-phase amorphous steel core transformer

Abstract: The use of amorphous ferromagnetic alloys in transformer construction allows reducing no-load losses by 4 times or more. At the same time, the magnetization curve of amorphous steel has a shape that is close to a rectangle, which significantly distorts the shape of the no-load current curve. This is accompanied by inrush current increases when a saturated transformer is turned on. However, there are no publications devoted to this issue in the periodicals. The purpose of this work is to develop a dynamic model and study the dynamics of an amorphous steel core single-phase transformer (TAS) operating at an arbitrary external load. The calculation of the electrical circuit was made by a one-step method based on a modified 2nd-order Rosenbrock formula, and the circuit parameters were calculated by the finite element method. We have developed dynamic models of the single-phase transformer based on the use of controlled current sources and EMF and implemented in the MatLab Simulink SimPowerSystem. These models allowed us to take into account the effect produced by the practically rectangular shape of the magnetization curve of the amorphous steel used to make the core on the operation of a saturated transformer. It has been established that the inrush current occurring when a saturated TAS is switched on can exceed the rated current tenfold. A significant distortion of the current curve has been detected in the first periods even when the transformer operates at nominal load. The developed models can be used to study the operation of a transformer at an arbitrary load. These models can be developed further. It has been found that a significant effect on the transformer operation is produced by the shape of the amorphous steel magnetization curve.

Influence of design parameters and operating conditions on performance indicators of magnetic fluid seals of electric motor shafts

Abstract: Magnetic fluid seals (MFS) are beginning to be used to seal rotating shafts in electric motors operating in conditions of high humidity, dust and pollution. Friction torque and heating are the most important operational indicators of MFS depending on the design parameters and operation conditions: rotation frequency, operation time, temperature and clearance (taking into account roughness and waviness). An urgent task is to study the influence of design parameters and operating conditions on the performance indicators of MFS of such electric motor shafts. The modeling of rough surfaces was performed using orthogonal transformations of roughness matrix vectors and a visual representation. The contact area of the magnetic fluid with rough surfaces was determined by mathematical modeling. The experimental studies were performed on a test bench. Wear sleeves and poles made of various steels with different roughness parameters were used. Models of MFS clearances formed by surfaces with different roughness have been obtained. The contact areas of the magnetic fluid with the surfaces of MFS at different roughness values have been determined. Nonlinear dependences and variation limits of the friction torque and MFS temperature on the surface roughness of the poles and sleeves, rotation frequencies of the electric motor, and the external temperature have been obtained. Clearance models allow determining the roughness of MFS surfaces. The developed experimental unit allows carrying out studies on the effect of changes of design parameters and operating conditions on the performance indicators of MFS. At a 5,21 time higher rotation frequency (from 556 to 2897 rpm), the MFS temperature can increase by up to 2 times, the friction torque – by up to 2,2 times. If the temperature rises by 50 оC, the friction torque can drop by up to 3 times. With an increase in the surface roughness from 0,357 to 7,21 μm, the temperature of the MFS can rise by 20 %, and the friction torque by 55 %.

Experimental determination of partial discharges in a model of a digital instrument transformer by differential method

Abstract: Power facilities are now implementing the concept of smart grid and its essential elements – high-voltage digital current and voltage transformers. However, the implementation of digital technologies is slowed down by the lack of operation experience and reliability indicators. One of the main causes of high-voltage equipment failures is insulation damage. The most informative parameters determined by insulation evaluation are partial discharge characteristics. There are rated values of these characteristics for rotating electrical machines and power transformers measured by external equipment. But the existing method of partial discharge analysis cannot be applied to digital current and voltage transformers as there are no criteria for tripping of the innovative equipment with comprehensive insulation. All this urges us to study the possibility to determine experimentally the characteristics of partial discharges in the insulation of digital current and voltage transformers by using embedded inductive sensors in order to develop a method for condition monitoring of digital current and voltage transformers and improving of their reliability. In this work, we have used a model of digital current and voltage transformers, a high-voltage test unit, a digital multi-input oscciloscope and inductive sensors. The experiment includes: detecting partial discharges in the model of digital current and voltage transformers by the external bridge connection, recording the voltage at which partial discharges occur in the simulated fault area, measuring the corresponding value of the apparent charge of the partial discharge, detecting partial discharges in the model of digital current and voltage transformers by a differential method with the help of embedded inductive sensors. The characteristics of partial discharges in the simulated fault area have been experimentally determined on a model of digital current and voltage transformers. The pulse voltage on the embedded inductive sensor corresponding to the apparent charge of 80 pC was equal to 600 mV at the test voltage of 2,7 kV. Embedded inductive sensors allow implementing the method of insulation condition monitoring for digital current and voltage transformers in accordance with the partial discharge characteristics both at the stages of production and operation extending the potential of the electronic (microprocessor) module and increasing the reliability of digital current and voltage transformers.

Method of condition monitoring of rotor windings of the medium voltage induction motors of power plant auxiliaries in start-up modes

Abstract: A promising method of monitoring rotor winding condition of induction electric motors ensuring higher reliability of their operation is spectral analysis of the external magnetic field signal. Modern methods of external magnetic field analysis use only the spectrum of this signal in the steady-state operation mode, which does not allow effective monitoring on a number of medium voltage electric motors of power plant auxiliaries operating with long start-ups (for example, machines with variable load, with a double squirrel cage, etc.). It is possible to evaluate the rotor winding condition of such machines in start-up modes, which means that an important task is to study the frequency-time spectra of the external magnetic field of the above-mentioned electric motors and to develop a method for monitoring the state of their rotor windings in the startup mode. In the study, the authors used two-dimensional models of two different types of motors representing drives of the mechanisms of draft systems at power stations. Both models are developed in the ANSYS software package. The calculation of the external magnetic field was carried out using the finite element method. The modelling was done for cases with or without defects. Signal processing was per-formed using the Fourier window transform method in the MatLab software package. Frequency-time spectra of the external magnetic field were built in the start-up mode on models of the investigated induction motors with the following defects: with dynamic eccentricity, with one broken bar of the rotor winding and without the indicated defects. The research results allowed us to develop a method for monitoring the rotor winding state of medium voltage electric motors of power plant auxiliaries operating with long start-ups. The method is based on detecting lower side frequencies of the fictitious rotor winding harmonics in the frequency-time spectrum during the startup. Their specific feature is «reflection» in the spectrum from the time axis. The developed method of monitoring rotor winding condition of the above-mentioned induction electric motors allows increasing the reliability of their operation by timely detection of faults in the rotor windings.

Methods of monitoring water conditions of the circulatory cooling system of a combined heat and power plant

Abstract: A common method of preventing scale formation on the internal surfaces of the condenser and heat ex-changers at thermal power plants with circulatory cooling systems (CCS) is correctional treatment with an addition of sulfuric acid for acidifying make-up water and reducing its alkalinity and the alkalinity of recycled water and dosing of oxyethylidenediphosphonic acid (OEDFK) for preventing scale deposit formation. The existing method of correction treatment does not provide the necessary degree of heat exchange equipment protection from scale formation. With this method of cleaning, it is impossible to completely remove deposits from the surface of the tubes to «pure» metal; the concentration of sulfates in the purge water often exceeds the permissible level. Improving the efficiency of water conditions requires developing a calculation method and creating a pilot plant for monitoring scale formation and corrosion through estimation of water chemistry directly in industrial conditions, which is the goal of this work. The circulating water corrosivity was studied on a stand that simulates the operation of circulatory cooling systems. The coil simulating water movement inside heat exchangers contained carbon steel and brass corrosion rate witness plates. A quantitative assessment of the biological contamination of the circulating water of the cooling system of the CCPP ПГУ-450 MW was carried out using total bacterial count (TBC) express tests. To estimate the probability of carbonate salt deposition in heat exchange equipment, we have proposed a method of calculating the existing values of the stabilization factor (calcium transport). The proposed method has been used to estimate the state of water chemistry of the circulatory cooling system of CHP PGU-450 MW. Calculations confirmed by the data of chemical analyzes of water and deposits have shown increased deposit mass values on the control samples (stabilization factor less than 85 %), including biological ones (the total bacterial count exceeded the permissible value by over 104 CFU / ml). The circulating water corrosivity also increased, and the corrosion rate of steel st. 20 exceeded the standard values (0,1 mm / year). The developed technique can be effectively used for analyzing the state of both the existing water conditions of circulatory cooling systems, and any other (alternative) water chemistry directly in industrial conditions of operation of a certain CCPP.

Development of the furnace design for solid waste utilization and evaluation of its operation efficiency

Abstract: Practical implementation of the process of thermal utilization of waste, including municipal waste, and processing efficiency largely depend on the plant design and operation modes. In their works, P. Basu, Safin R.G., Shantarin V.D. and others propose designs of plants for processing carbon-containing waste. The main disadvantage of such plants is the use of only one waste type (wood, biomass or plastic). Such plants operate at low humidity of the raw material, which lowers the quality of the produced gas. All this makes it an urgent task to develop a new plant design for disposing of waste of various compositions in a wide humidity range and to evaluate its performance efficiency. To evaluate the efficiency of the furnace for thermal waste utilization, we used the material and heat balance method that allows determining the plant efficiency and selecting the operation mode with the maximum efficiency value. This paper proposes a design of a two-chamber thermal reactor for waste utilization based on the combined method of drying and oxidative pyrolysis. The plant design allows you to organize the process of oxidative pyrolysis of raw materials in the reactor and to separate the flow of pyrolysis gas to the consumer from that for their own needs. The paper describes the algorithm of material and thermal calculation for drying and pyrolysis zones. It also presents an analysis of the thermal reactor with a capacity of 500 kg/h in different modes of oxidative pyrolysis depending on the moisture content of the feedstock. The developed plant design allows utilizing solid waste at its relative humidity from 4 to 50 % and reaching efficiency from 0,6 to 0,9 by changing the amount of oxygen fed inton the system from 1 to 10 %.

Influence of gas flow oscillation on the efficiency of particulate solids treatment in a circulating fluidized bed

Abstract: Apparatuses with fluidized bed are widely used in the solid fuel energetic, chemical and other industries. In particular, fluidized bed furnaces play the increasing role for thermo-chemical treatment and burning the solid fuels including bio-fuels. The use of pulsating gas flows is one of the possible ways to intensify the process of gas-particle interaction. However, the efficiency of the way is not always obvious, and new approaches are needed for preliminary estimation of its advantages. The method of mathematical modeling is used to solve the above problem. The model is based on the set of differential equations of a single particle motion in the upstream gas flow with variable with time velocity, and with variable with time particle properties due to this or that thermo-physical or chemical process of gas-particle interaction. The study of influence of the process parameters on its efficiency is done by numerical methods. The model of the effect of oscillations in the gas flow on the efficiency of particle processing in a circulating fluidized bed has been developed. The necessary time for enough particle treatment is compared for different amplitude and frequency of gas flow oscillation. The most considerable gain in time is being reached for the strong dependence of the reaction rate constant on the velocity of flow around the particle. In this case the optimum frequency of oscillations exists that give the maximum gain in time. The growth of the amplitude leads to the monotonic increase of the gain in time, or gives the optimum amplitude. Transition to the pulsating gas flow in a circulating fluidized bed reactor leads to considerable gain in time of particle treatment only in the case of strong dependence of the reaction rate constant on the velocity of flow around the particle. In this case the optimum frequency and amplitude of oscillation exist that gives the maximum gain in time.

Impact of distribution of impurity particles on electric strength of transformer oil

Abstract: To extend the service life and ensure the operability of oil-filled transformer equipment, the attention is paid to the development of methods for monitoring the state of oil-barrier insulation. When monitoring the technical condition of transformer oil, the class of liquid purity is determined depending on the rated voltage of the equipment. However, the influence of the parameters of mechanical impurities on the breakdown voltage is not taken into account, thereby lowering the requirements for the quality of oil barrier insulation. This makes it relevant to study the influence of the size distribution of impurity particles on the electric strength of the internal insulation of power transformers and determine the parameters of particles of mechanical impurities to justify the underestimation of the quality indicators of transformer oil in operation. Methods of mathematical statistics were employed using the Gnedenko-Weibull distribution based on the standard values of liquid purity classes. To determine the maximum and minimum voltages, the standard values of the average breakdown voltages and the results of operational tests of transformer oil in a standard spark gap were used. The relation between the particle size of mechanical impurities and the breakdown voltage of transformer oil has been established. The particle size distribution of impurities has been obtained for 12 and 13 classes of liquid purity for power transformers with a voltage of 110–750 kV. The particle size range that defines the maximum and minimum breakdown voltages has been determined, and the values of limit concentrations of mechanical particles have been established. The obtained parameters of impurity particles which determine the maximum and minimum breakdown voltages of the operating oils can be used to evaluate the technical condition when diagnosing the internal insulation of power transformers in order to increase their operational reliability, as well as to adjust the regulatory requirements for the quality of operational transformer oil according to the content of mechanical impurities.

Design of power substation placement with GIS tracing tools

Abstract: Analytical methods that are currently used to determine transformer substation placement in the process of planning the development of low-voltage distribution networks are based on calculating the lengths of future power lines by Euclidean distance, or methods for comparing several alternative placement options taking into account the routes of power lines. Assumptions made in this case lead to the fact that for the selected location of the substation, the total cost of the power lines connected to it may exceed the possible minimum. The use of modern GIS technologies allows simulating the routes of laying power lines on the map bypassing the existing obstacles or finding the cheapest routes for crossing them. These opportunities can be used to improve the quality of designing urban distribution networks through minimizing the construction cost of new power lines. However, the methods of organizing the solution to such a design problem have not yet found practical applications. The aim of the work is to develop a practical method of designing the placement of power substations in the GIS environment and its verification using real data. The paper uses methods of spatial modeling in the GIS environment, including methods of overlay, finding optimal paths on graphs and power grid inventory, as well as discrete optimization methods. A method of computer-aided design of transformer substation placement in urban distribution low-voltage networks is proposed and implemented as a GIS software module, which allows finding the optimal options of the placement cost at the stages of network scheme selection. The paper presents the results of the method analysis based on studying the design of the power grid scheme of Ivanovo city quarters as an example. The results confirm the possibility of using GIS to improve the quality of decisions on the choice of placement of low voltage distribution substations when designing urban electrical networks and can be used in the electrical networks CAD.

Method of winch drive permanent magnet inverted motor design

Abstract: Designing a permanent magnet synchronous motor (PMSM) of a winch drive needs to take into account the features of this machine. The engine has an inverted design with limited dimensions, is powered by a fre-quency converter, runs at the nominal power frequency and nominal load without using the damping winding and frequency start, and provides the required range of rope winding speeds. There is no specialized engi-neering design methodology for the winch drive PMSM. It is required to make changes and additions to the existing methods of designing synchronous machines when solving the problem of designing a winch drive PMSM. Design and validation calculations were performed in the Mathcad environment based on the tech-nique of designing machines with V.A. Balagurov’s permanent magnets and methods of designing general-purpose industrial synchronous machines with electromagnetic excitation. Field models of PMSM were used for modelling electromechanical processes and thermal status. The developed technique of designing the winch drive permanent magnet inverted motor is different from the known methods and due to this allows accounting for the design features of PMSM in the calculation of the size of the machine, the magnets, the stator core, the choice of electromagnetic loads, the design of the stator winding, the choice of the cooling system and the steel grade of the stator core. The specific requirements of the technical specification are taken into account when calculating the number of poles and the frequency of the supply voltage. A design project of the inverted PMSM of the winch drive has been developed. And the paper presents the design and verification calculations results. The reliability of the results was checked by field modeling of electromechanical processes and the thermal state of the PMSM. The study has solved the problem of no specialized engineering design techniques of the winch drive PMSM. The technique can be used by electromechanical engineers in solving the problem of designing winch drive PMSM as it allows making a design project of the PMSM corresponding to the requirements of the technical specifications and operation feature.

Development and study of the fault location function for the information system based on digital transformers

Abstract: The existing methods of fault location (FL) on power lines are often unable to provide the required accuracy and are unstable to the influence of metering-distorting factors. The main source of errors of the FL devices is the primary current and voltage transducers. Using innovative current and voltage sensors (including Rogowski coils for physical measurement of the primary current derivative) as part of digital measuring transformers allows significant improvements in the accuracy of measuring electrical values during short-circuits. The aim of the work was to develop an enhanced accuracy FL function as part of an information system (IS) that takes into account the characteristics of non-traditional primary converters and, in general, digital current and voltage transformers. The methods of the electrical circuit theory, mathematical simulation and physical-mathematical modeling are used. The computer experiments are carried out in the modern modeling systems Matlab + Simulink and RSCAD, and the physical and mathematical modeling – in the real-time modeling complex RTDS. For modeling power transmission lines, the specific parameters were assumed to be known and unchanged. The developed FL function differs from its analogs as it uses information signals from digital current and voltage transformers, is characterized by operation stability under the influence of some metering-distorting factors (presence of transient resistance, changes in electrical load, breakdown phase, presence of capacitance of phases to earth, etc.) and an error not exceeding 8 % (at large distances and in the presence of transitional resistance in short-circuit locations) or 3 % (in the absence of metering-distorting factors). A prototype of the IS with the FL function has been designed and experimentally tested. The developed FL function allows increasing the accuracy of short-circuit location determination and reducing the time of finding the fault. Fault location IS data can be used by the operating personnel of electrical networks. The reliability of the obtained results is determined by the methods of the classical electrical circuit theory and the theory of electromagnetic transients in electrical power systems, and by the convergence of the results obtained in the study of the function accuracy in different modeling complexes.

A laboratory study of environment and voltage effects on the thermal state of resistive voltage divider

Abstract: There are currently no thermal self-diagnostics systems of instrument transformers operating in real time, as opposed to power ones, and thermal inspections are often carried out according to a maintenance schedule, which affects the reliability of electrical equipment. Therefore, an important task is to create such systems for digital instrument combined current and voltage transformers based on resistive dividers, which determine temperature values at several points, including the most heated element. The aim of this study is to obtain experimental data on the thermal state of a resistive divider exposed to environmental factors and voltage for developing a self-diagnostics system. The results are obtained by physical simulation of thermal conditions of the transformer and its elements in high- and low-voltage climatic chambers. The effects of the following factors of critical importance have been simulated: electric voltage, insolation, temperature and speed of the ambient air. Data processing was performed using the methods of probability theory and mathematical statistics. The time needed for the thermodynamic system to move to a steady heat exchange mode, and also the temperatures on the lower resistors and on the surface of the voltage transformer insulation cover have been determined. It has been established that thermal conditions are more significantly affected by the simulated voltage than by insolation. The study has shown that even in the most severe emergency operating modes, heating in the lower resistor does not exceed the critical value. It has been found that the thermal state of the transformer is significantly influenced by the simulated factors including directional insolation, which is not taken into account in the existing methods of calculating the thermal state of the instrument electrical equipment. The reliability of the obtained results is ensured by the fact that the simulation took into account significant factors. The results of the experiment will be used to develop a thermal self-diagnostics system for the digital transformer, which will improve the reliability of operation of such instrument equipment by allowing the personnel’s to give a rapid response to real-time information about the transformer thermal state.

Magnetic spring effect on the force characteristics of the electromechanical magnetic liquid damper

Abstract: The effect of a magnetic spring is observed in electromechanical devices with limited pole sizes. Simultane-ous changing of the system magnetic conductivity after a relative displacement of the poles causes mag-netic tension forces. These forces in electromechanical magnetic fluid dampers have their own specific characteristics which have not been studied before. All this requires studying the effect of a magnetic spring on the damper power characteristics, estimating the effect of the properties of a magnetorheological suspension on the magnetic spring strength, nature of its change and combination of the action of magnetic forces and viscosity resistance to the piston movement. To do that, it is important to analyze the effect of a magnetic spring in statics, at a slow movement of the piston and its dynamic oscillations. The studies were based on the theory of natural experiment and methods of processing experimental results. We have obtained and analyzed dependences of the resistance force of the electromechanical magnetic fluid damper for different vibration frequencies and magnetic inductions. The effect of magnetic spring forces on the damper power characteristic has been investigated. It has been found how the damper resistance force is affected by the magnetic and hydrodynamic components. The use of a damper with alternating elements with high and low magnetic conductivities makes it possible to change the strength characteristic of electromechanical magnetic fluid dampers. The proportion of the force controlled by the magnetic field reaches 75 % of the total effort. The use of the magnetic spring effect allows increasing the damping efficiency at small amplitudes and vibration frequencies. Increasing the magnetic properties of a magnetorheological suspension enhances the effect of a magnetic spring if the piston is non-magnetic, and weakens it if it is a magnetic one. When the magnetic induction rises, the effect of the magnetic spring increases. By changing the initial piston position, it is possible to obtain an asymmetrical power characteristic, for example, without using valves and spools, to increase the rebound force and to reduce the compressive force. If there are no moving parts, the damper reliability increases.

Improving the accuracy and time of calculating steady-state modes of increased frequency electrical systems

Abstract: The authors of modern Russian and foreign works suggest using the method of frequency analysis with Fourier transforms for modeling alternating current systems with a non-sinusoidal supply voltage. By applying the above-mentioned method to calculating steady-state modes of increased frequency power electrical systems (IFPES), we have found that there are significant differences between the calculated and experimental results, and the model calculation time is long. These problems can be solved by obtaining generalized formula expressions for the internal resistance value of IGBT transistors and the amplitudes of the acting EMF (voltage) in the IFPES applying Fourier decomposition. The generalized expressions for determining the internal resistance of IGBT transistors were obtained by analyzing physical processes of charge diffusion. The amplitude of the acting EMF (voltage) was determined by numerical integration. Simplified analytical expressions suitable for determining the frequency dependence of the resistance of IGBT transistors in the open state in electrical devices have been obtained. The IFPES calculation rate model has been optimized by frequency analysis. The obtained generalized analytical expressions allow making more accurate calculations of the transistor internal resistance value (with a difference of 70 % compared to the previously used value). By optimizing the calculation method we were able to reduce the model calculation from 8 hours to 3 minutes with Nk = 3000 harmonics. The modernized method can be used not only for calculating the IFPES but also for analyzing any electrical circuits with power electronics components exposed to non-periodic and non-sinusoidal currents and voltages.