Elements Of Electric Power Systems Research Articles

Research of the distribution symmetrical components in an electrical system with a diesel generator at an unsymmetrical load

Purpose. Investigation symmetrical components of current and voltage in microgrid elements with an autonomous synchronous generator of limited power, which works in parallel with a network transformer under the condition of non-metric load. Methodology. During the research, visual programming methods were used in the Simulink/Matlab package, methods of electrical engineering theory in terms of determining symmetrical component currents and voltages in observation branches, methods of synthesizing schemes for replacing elements of electric power systems for symmetrical component currents, methods of data processing and construction diagrams using specialized software tools.. Findings. As a result the analysis known studies, it was established that under the condition of researching low-power generating systems in conditions of asymmetry, insufficient attention is paid to the nature of the asymmetric load. Using the well-known structure of a microgrid, which includes a synchronous generator, a machine load, and an external network transformer, its model was built, in which, by introducing asymmetric loads of various types, a series of experiments was implemented with the registration of voltages and currents of forward, reverse, and zero sequences in the branches of the network. The analysis of the results obtained during the research established that the positive sequence voltage in the case of a change in the active load does not change its level, under the same circumstances, in the case of an active-capacitive and active-inductive load, the voltage change has the opposite character. In the case of increasing asymmetry of an active-inductive nature, the positive sequence voltage decreases, and in the case of an active-capacitive one, it increases. The specified changes in some cases exceed 3%. Positive sequence currents in the case of active load imbalance differ slightly. In the case of a positive sequence current of the transformer, its continuous growth is observed, which in the case of active-capacitive and active-inductive loads exceeds the active one by an average of 1.5 times. Negative sequence currents in the studied model, which are formed by an asymmetrical load, are completely closed to the transformer, causing zero-sequence voltages, and the nature asymmetrical load significantly affects the value of these currents, a 61% increase was noted. Originality. It was established that in a microgrid, which includes a synchronous generator, a machine load, a symmetrical active load of comparable power to the generator, an external network transformer, in addition to the fact of asymmetry caused by an asymmetrical load, the character of an asymmetrical load (active, active-inductive or active-capacitive). Practical value. In the case of using in microgrids devices that provide an increase in the quality of electrical energy, for example, symmetrical devices, it is necessary, in addition to the asymmetry factor, to take into account the natural load that causes the latter.

The Tools and Parameters to Consider in the Design of Power Transformer Cooling Systems

Transformers are the most important elements of electric power systems. Many conditions must be met for power transformers to work properly. One of them is a low operating temperature. This condition will be met if the transformer cooling system is properly designed. One of the components of a cooling system is insulating liquid. The heat transfer coefficient α of liquid determines its ability to cool the transformer. The higher its value, the more effectively the liquid transfers heat to the environment. This article describes the influence of the position of the heat source, which is usually in the windings of the transformer, on the coefficient α value of the insulating liquid. The vertical and horizontal positions of the heat source were analyzed. The coefficient α was analyzed at different points of the heat source. The tests were carried out for mineral oil and various esters. Heat transfer coefficient measurements were carried out for various surface heat loads of the heat source. It has been proven that, in the case of a horizontal heat source, the coefficient α has a value several dozen percent higher than in the case of a vertical source. It has been proven that the coefficient α has different values in different places of the heat source. Regardless of the location, the highest value of the coefficient α occurred in the lower part of the heat source.

Fault detection in a power transformer based on reverberation time

The power transformer is one of the vital elements of electric power systems. The reliability of power transformer operation is directly related to its condition. Detection of winding deformations is possible by means of sweep frequency response analysis. Interpretation of SFRA results is usually performed by visualization of images generated using specialized devices and comparison of transfer functions obtained from successive tests. This diagnostic method is known as a fingerprint and its disadvantage is the subjectivity and relying on engineer’s experience. This paper presents an experimental approach for detection of internal transformer short-circuit faults. Existing mathematical indicators based on frequency response analysis are often unable to unambiguously indicate the degree of fault and their determination requires high-cost measurement and signal processing equipment. A new indicator based on the reverberation time, commonly employed in acoustics, is proposed instead. The proposed parameter is based on time-domain calculation and enables reliable detection of transformer inter-turn short circuits and accurate estimation of their degree. A significant advantage of the proposed approach is its low dependence on the frequency range of the measured signal, which allows employment of low-cost measuring and signal processing devices.

Technical and economic optimization of fuel facilities – energy complex using elements of fuzzy logic and artificial neural networks

This article discusses the possibilities of optimizing the fuel and energy complex by improving the accuracy of the forecast of the state in both the operational and medium-term periods: from an hour to several years. The model used to implement the mentioned energy efficiency improvement is based on the use of fuzzy neural networks together with the function of minimizing power losses in the elements of electric power systems. The Mamdani modification is used, which takes into account the database of previous periods of the system state, represented as static load characteristics. The organization of this approach allows you to take into account weakly formalized factors, thereby improving the quality of forecasting and dispatching management. At the same time, it is possible to use models for a wide class of objects, which is achieved due to its scalability. The estimation of forecasting accuracy of the proposed approach exceeds similar indicators of currently used statistical methods and regression implementations. These factors are direct economic drivers of reducing production costs.

Estimation of the short circuit accident probability at the overhead electric transmission lines

The object of research is the probabilistic characteristics of the occurrence of a short circuit (SC) on overhead electric transmission lines (ETL) of voltage classes 110 kV and higher, the failure of which can lead to the development of an accident in the electric power system (EPS). The probabilistic characteristics of the SC occurrence on ETL depend on a large number of factors: the length and route of transmission of power lines, voltage class, weather conditions, and the qualifications of the staff in which charge, management and maintenance the power lines are located. The most problematic issues in assessing the SC occurrence on overhead power lines is the allocation of damage from a SC with general damage statistics, the quantitative consideration of such features of the functioning of overhead ETLs, such as meteorological conditions, the staff qualification level and the technical condition of a single piece of equipment.In the course of the study, a fuzzy-statistical approach is developed to assess the SC occurrence on an overhead power line taking into account its individual characteristics of work, such as the staff qualification level, meteorological conditions of operation and the technical condition of the power line. To determine the unconditional probability of SC occurrence on an overhead ETL, statistical data on SC on lines of the corresponding voltage class are used. The technical condition of the power lines and meteorological conditions of operation are quantified by fuzzy models, the staff qualification level is determined at standard intervals of the Harrington scale. Conditional probabilities of the state of functioning of power lines are determined using a simplified fuzzy conclusion, which makes it possible to quantify the conditional probability in the absence of clear analytical relationships between the signs of the conditions of power lines.The results obtained by the developed approach are recommended to be used in the goals of risk-oriented management of the EPS to increase the reliability of operation by reducing the risk of developing a system accident when a SC occurs in the EPS elements. Also, restrictions on the application of the developed approach to the problems of assessing the probability of equipment failure and the organization of risk-based management are identified.

A Simulation Method of Steady-State and Quasi-Steady-State Modes of Electric Power Systems

An algorithmic implementation of a method of calculation of the modes of electric power systems with arbitrary structure is considered based on nodal-voltage equations, which is distinguished by the absence of reduction of the elements of electric power systems to each ratio transformation step. The interaction of electrically connected elements is arranged by the electrical parameters of the mode (of currents and voltages). The calculations of the modes of electric power systems are based on the solution of equations formulated based on the method of nodal-voltage equations. Based on analysis, the model was selected in the form of complex nodal-voltage equations as the balance of currents when setting a load by constant conductivity using topological matrices. As a result of proposed approach, the currents and the voltages of the branches are expressed through the components along the longitudinal d and the transverse q axes, the transition to instantaneous values of currents and voltages is carried out using a coordinate transformer by Gorev’s formulas. The representation in the d and q axes makes it possible to use directly the catalogued data of equipment when simulating synchronous machines. The method can also be used when tuning the excitation control systems of generators to check the correspondence of the excitation voltages of the system to the nodal voltages. It is proposed to develop the model of electric power system to the level of simulation of transient processes in structural elements at which the equations in the Park–Gorev coordinates are predominantly used.

Use of an analytical method for calculating reliability of elements of electric power systems based on probabilistic models

Today, we no longer have to prove the need for numerical evaluation of reliability of in-plant power supply systems. There have been established generally accepted reliability indices in the form of frequency of various accidents and mathematical expectation of undersupply of electricity to consumers, or decrease of power generation by plants. Factors are revealed factors that must be considered at analysis of reliability of power supply systems: availability of repair of switching circuits and duration of repair of the main equipment and switching equipment, failures of switching devices and devices of relay protection and automatics, routine switching, seasonal variations in damage to overhead lines and outdoor equipment. Here, one should take into account a possible lack of reliable initial information about the reliability of elements at the consideration of a specific installation. The paper formulates models of the analytical method of calculation of reliability parameters of elements of power supply systems in the Matlab software. Reliability models are considered for power units, which involve restoration and prevention activities. Three states of a system are considered: operable state; emergency downtime and recovery, scheduled downtime for preventive maintenance or repair subject to intensities of emergency and planned outages, intensities, recovery and completion of scheduled maintenance and repair. It is shown that, at present, targeted screening and quantification of contributions to unreliability of power supply systems by failures of elements of the system, its states and modes, as well as effectiveness of various measures, allow to identify weak links of the power supply systems and to work out specific ways for improvement in the process of human-machine synthesis of the power supply system. This approach to design involves searching for new circuit solutions, and changes in the structure of the circuit and layout solutions of its equipment mitigation of weaknesses, elimination of excessive equipment, or, on the contrary, using more reliable equipment, as well as its modernization.

PRINCIPLES OF IMPLEMENTATION OF BLOCKING OF CURRENT PROTECTION OF ELECTRICAL POWER UNITS WITH TRANSFORMERS

Principles of implementation of current protection of elements of electric power systems with power transformers are considered. In some cases, in facilities with power transformers there could be an inrush of a magnetizing current that can cause a false positive current protection. The special measures of blocking of current protection ought to be taken to avoid this. The methods of implementation of blocking digital current protection when magnetizing current inrush takes place are described. The main way of blocking protection from magnetizing current inrush is tuning-out by harmonics content. The presence of lower harmonics content serves as a criterion of permitting operation of the protection and the higher harmonics content, on the contrary, indicates the appearance of magnetizing current inrush and is used to block the protection action. The operation condition of blocking of digital protection from magnetizing current inrush is presented. A realization of digital part of implementation of current protection blocking is described and the functional scheme of the latter is considered. The scheme contains conditioners of orthogonal components of signals of the first and second harmonics as well as the filters of positive and reverse sequences and blocks of determination of amplitudes. The blocks compute current amplitudes of first harmonic of positive sequence and the negative sequence current of the second harmonic with the use of the orthogonal components. By these values the characteristic quantity of blocking is calculated, which is compared with the activation setpoint. The improvement of performance of the principles of blocking current protection of electric transformers with current magnetizing inrush has been suggested by incorporating the digital part the block of the maximum value formation that determines the maximum amplitude of the first harmonic of the total current into the functional block scheme.

Software and Hardware Complex for Setting of Automatic Excitation Regulators of Turbogenerators

The motivation of the presented research is based on the needs for development of new methods and tools for research setting problem of automatic excitation regulators of turbogenerators. Simulation tools must meet the requirements of reproduction processes reliability in all elements of electric power system. The developed block diagram of the adequate mathematical model of automatic excitation regulator is presented. The simulation results of electric power system scheme confirm the adequacy of the reproduction processes of functioning of automatic excitation regulator and a generator.

Magnetic Field Measurement from 132 kV and 275 kV Overhead Transmission Lines Within Residential Area

Overhead transmission line (OTL) has been around for so many years as one of the most important elements of electric power systems. Conductors, as being a part of the medium to transfer electricity through the OTL, produces electromagnetic field to its surrounding that have been a public concern for ages. OTL were meant to be built as far away from a population. Though from time to time, the OTL rights-of-way (ROW) were violated due to lack of space and rapid urbanization. This paper addresses the challenges faced during magnetic field level measurement within a residential area that was still under construction. EMDEX II Meter, Linear Data Acquisition System (LINDA) Wheel and Gauss Meter were used during the magnetic field measurements. Maximum magnetic field level data collected from measurement were presented.

A method for development of software packages for mathematical simulation of electric power systems

Methods for development of program simulator complexes for mathematical simulation of power systems based on graph theory and structural simulation principles are developed and discussed. The form of equations to describe the dynamic interaction model for the structural elements of electric power systems is suggested and proven. The proposed form provides a model-independent and universal mathematical description. Simulator complexes that are based on the developed technique are discussed. Their characteristics and purpose are discussed. Simulator complexes provide additional possibilities beyond actual simulation, including the possibility of making rapid changes in the structural topology of the system by the user, automatic calculation of parameters for multivariate tasks, accounting protection algorithms, development of simplified models for a variety of settings of automatic control systems, and automatic tuning and optimization of control algorithms.

Classification of lightning stroke on transmission line using multi-resolution analysis and machine learning

One of most important elements of Electric Power Systems (EPS) is the transmission line (TL), which is permanently under adverse conditions especially lightning strokes. At the moment, those phenomena have been the root cause of short circuits and the most important cause of mal-operation of transmission line protection relays. Thus, this paper develops the classification of lightning transient signals with and without fault. Multi-resolution analysis (MRA) is used to analyze those signals considering five mother wavelets and different decomposition levels of three phase voltages. In this manner, Spectral Energy and Machine Learning as Artificial Neural Network, K-Nearest Neighbors and Support Vector Machine are employed to classify those signals. On the other hand, the developed work in this paper analyzes most important parameters of lightning strokes, which are essentials in producing conditions with and without fault. Results show that the methodology presents an acceptable performance.

Stochastic generation-expansion planning and diversification of energy transmission paths

The paper addresses a stochastic generation-expansion planning model in the interdependent operation of an electric power system (EPS) and a natural gas system (NGS). The objective of the proposed optimization model is to provide consumers with a reliable electric energy supply by proper generation-expansion planning and diversification of energy transmission paths with minimal investment and operating costs. The proposed method takes into account constraints in the EPS and NGS. The Monte Carlo simulation method is applied to consider random outages of EPS and NGS elements and inaccuracies in the long-term electric load forecasting. A scenario reduction technique is used for reducing the computational burden of a large number of planning scenarios. The EPS and NGS are presented by a direct current (DC) model and a transportation model. The optimization problem is decoupled into a master problem and a subproblem using the Benders decomposition to cope with large-scale problems. The master problem deals with the optimization of investment in new generation units and energy transmission paths. The subproblem comprises a two-level optimization with a decomposed EPS reliability check as the master problem of the subproblem, and a NGS reliability check as the final subproblem. The case studies illustrate the applications of the proposed stochastic method in a coordinated generation-expansion planning problem when considering uncertainties.

Simulation of transient processes on overvoltage in electric transmission lines using ATP-EMTP

In this paper, the mathematical modeling and simulation of electromagnetic transient processes is considered, which is of vital importance for examining the overvoltage phenomenon of power transmission systems. In the mathematical models of the AC power transmission systems that contain a power source, the power transformer, transmission line, and power autotransformer block are presented. The mathematical model of each system component is obtained based on the branch voltages, flux linkages, and branch voltages of the magnetic circuits individually. As for the simulation, an alternative transient program (ATP) environment is used to model the electric power system's elements. One of the power system's overvoltages occurs because of the fault and switching events. The usage of reactors at the sending and receiving ends of the line limits the overvoltages. The ATP has a powerful tool to simulate the transient events: specifically, the fault transients in the time domain. In order to test the simulation model's performance, the overvoltage measurements from a field test of a 500 kV electric transmission system is used. The simulation shows that the obtained results give satisfactory solutions to investigate the power system's overvoltage events. Selected results of the evaluation are presented.

Modeling of the interaction of structural elements of electric-power systems

A form of equations to describe the dynamic interaction model for the structural elements of electric-power systems is suggested and proven. The proposed form provides a model-independent and universal mathematical description.

Joint operation of the superconducting fault current limiter and magnetic energy storage system in an electric power network

An opportunity of using superconductors as active elements of electric power systems designed to control the electric power distribution, to enhance the systems operating modes and to limit fault currents, was very attractive for investigators for a long time. In this paper, is considered an opportunity to enhance the electric power systems with the aid of superconducting magnetic energy storage systems (SMES) and superconducting fault current limiters (SFCL) operating together. It has been shown that the joint operation of both these superconducting devices allows additional varying of their parameters, what in turn gives a further opportunity to reduce their mass and dimensions and consequently the costs. There had been also shown an additional advantage of the SMES and SFCL joint operation consisting in that they ensure a more effective protection for a power system, preventing its uncontrolled load-off and subsequent acceleration up to the inaccessible rotation speed.

Designing a New Post Insulator Using 3-D Electric-Field Analysis

Insulators are very important elements of electric power systems. This paper introduces an analysis of electrical conditions in the area between the conductor and the insulator's upperfitting. The designing of new a composite post insulator is presented with the upperfitting made of insulating material. Previous composite post insulators have had upperfittings made of conducting material metal. 3D analysis of electric-field strength in the insulator and its surroundings are also given. The computation was carried out by using the OPERA Vector Fields program tool. The results of this analysis are presented for both-new and old versions of a composite post insulator. 3D analysis shows that the new version has up to five times lower magnitudes of electric-field strength.