Computer Simulation Of Voltage Unbalance Reduction In Power Supply Systems

The paper proposes а method for describing the process of reliable functioning of the enterprise’s power supply system by determining the permissible limit value of the current pulse for the satisfactory functioning of the power supply system. The main differences to the requirements of the electrical system of a modern enterprise are analyzed. Now mandatory requirements are equipment diagnostics, data transmission and, at a number of facilities, remote control, which can not be done without the use of high-performance microprocessor devices that set increased requirements for the operation of power supply systems. It is shown that the use of mechanical and semi-automatic devices to protect equipment is no longer enough, while modern systems have the ability not only to re-enable equipment, turn on backup power, but also adjust active and reactive powers using compensating devices, etc. It is shown how to find the slope of the straight line from the experimental probability and current impulse to determine the limiting value of the current. The operation of an information-measuring system that continuously monitors the behavior of the enterprise’s power supply system is shown. Recommendations are given on the application of the proposed method for protecting the enterprise’s electrical system. А structural-functional block diagram of an information-measuring system (IМS) for operational control with feedback of the quality of power supply of enterprises under conditions of random current consumption of its sections has been developed.

The parameters of complex power supply schemes of tram lines, which are required for simulation modeling, were studied: statistical characteristics of traction loads of feeders and voltage on the tires of traction substations. It was established that the distribution function of the feeder feeding the tram depot corresponds to the logarithmic normal law, the distribution function of the modules of the idle voltage deviation and the angles between the idle voltages of adjacent traction substations to the truncated normal law. It is proposed to modernize the information bases of electric traction network parameters with complex power schemes to increase the efficiency of modeling the modes of operation of sections of urban electric transport. A method of calculating instantaneous schemes has been developed, which allows to create algorithms that do not depend on the degree of complexity of the scheme. A method of simulation modeling of complex power supply systems of electric transport based on the synthesis of the matrix method of calculating instantaneous circuits and the method of statistical tests for modeling the organization of traffic of trams and trolleybuses is proposed. Algorithms and simulation models of traction power supply systems of urban electric transport have been developed, taking into account the modes of operation of power systems. A single simulation complex has been created that takes into account the traffic schedules of trams and trolleybuses, power flows in power supply systems, which makes it possible to obtain generalized dependences of power flows and energy losses, and to increase the accuracy of calculations of electrical parameters to 5–7%. Adequacy of the simulation model to the real process was verified by experimental data on a number of two-track, single-track sections of electric traction networks and complex power supply schemes of traction substations. The error in determining the integral indicators of costs and energy losses does not exceed 5%, and the rms currents – 3%. The use of simulation modeling in the design of traction power supply systems allows to improve the quality of electrical engineering calculations of complex power supply schemes and to propose energy-efficient power supply modes.

Forecasting the Risks of Stability Loss for Nonlinear Supply Energy Systems

The article is devoted to the development and testing of a methodology for analytical modeling of power supply systems that include multiple sources and multiple consumers of electricity, located at a distance from each other and connected by power transmission lines. The developed methodology will help designers assess the possibilities of distributing electricity among consumers while calculating the optimal voltages that need to be maintained at the nodes of the power sources, thereby achieving minimal voltage differences between the load nodes. The methodology is tested using a 10-node power supply system, in which the number of energy source nodes and load nodes is equal to 5. The modeling methodology is based on calculating the parameters of the power supply system using the node potential method, along with Ohm's and Kirchhoff's laws. The calculations utilize the method of complex amplitudes and are carried out according to a proposed iterative algorithm, the flowchart of which is presented in the article. The calculations are performed in the MathCAD environment using the mathematical framework of matrix computations. For this purpose, a conductance matrix and a node current matrix are constructed, and the node potential matrix is calculated in MathCAD. The paper demonstrates how to transit from a three-phase system to a single-phase system, with all calculations performed on a single-phase scheme. To obtain accurate results, formulas are derived for converting the parameters of the three-phase system into single-phase parameters, including the conversion of consumed load powers into complex impedances. The results of the modeling are presented in tabular form and as directed graphs, indicating the potentials of the nodes and the directions of active power flows. The results of modeling two variants of power supply systems are provided. The proposed methodology is recommended for assessing the parameters of power supply systems that include multiple sources of electricity and several load nodes. Keywords: power supply system, mathematical modeling, calculation methodology, node potentials, complex amplitudes.

The article is devoted to choosing ways to improve the technological reliability of regional electric network (REN) to ensure reliable power supply. At the operational stage, the task of increasing operational reliability is assigned to the enterprise asset management system of the territorial network organization (TNO), as a REN operator. Technological reliability is ensured by an operational dispatch control system, which uses the existing reserves in the network to support the technological process of electricity supply to electricity consumers in case of network equipment failures. The relevance of improving the technological and operational reliability of power supply system (PSS) requires the development and improvement of methods for analyzing and assessing the TNO's readiness to provide power transmission services. The indicators adopted in Russia reflect the level of technological reliability of PSS. However, these indicators do not reflect the technical condition of the equipment, or identify causal relationship between an equipment failure and an interruption of power supply. The research is aimed at identifying “bottlenecks” from the technological reliability standpoint and substantiating maintenance and repair, and technical re-equipment and reconstruction measures to improve operational reliability. A PSS model is proposed reflecting the technical condition of the network equipment, the operational readiness of automation systems, the availability of structural, functional and load redundancy in the REN. A method is suggested for calculating the PSS reliability indicators, where the developed indices reflect the degree of development of the network technical potential and the role of the aforesaid nodes in the PSS. The method makes it possible to identify the network parts, where it is necessary to introduce new technologies. In contrast to a well-known method, which is based on expert estimates of probabilities of different circuit-mode states of the network and on the calculation of normal and post-emergency modes, a less timeconsuming formalized procedure for analyzing and evaluating the network structural and functional reliability is proposed. The results obtained allow to increase the validity of the decisions made both at the operational stage and the design stage.

Modern motor vehicles are not equipped with devices that allow controlling efficiency of operation of power supply system, which leads to unexpected losses in operation. One of the solutions of the problem is continuous control of parameters of power supply system. However, their current values are not informative. On the basis of comparative analysis of power supply system parameters at normal and emergency operation the author suggests new principles of assessment of its efficiency. Results presented in the paper can get a practical development at realization of on-board device for monitoring power supply system for motor vehicles in real time.

Computer simulation is a method resorted to more and more frequently for the development of the prospective power supply systems, in particular the vessel power supply system. It provides valuable insights into the transient processes and indicators of electric power quality in the system without building its physical model, thus significantly improving the efficiency and quality of the physical model.Nowadays MathLab package with Simulink application is used with increasing frequency for simulation of such systems.The paper presents a model of the power supply system of small hydrographic vessel ‘Vaygach’ built in MatLab environment. The system vulnerabilities and their remedies have been identified. Changes in sinusoid before and after the non-linear load on the network have been demonstrated and solutions for improving the non-linear distortion factor are proposed. The model developed for the vessel power supply system can be used for building models of different vessels.

This paper analyzes the advantages of bilateral power supply systems for electrified railway. Firstly, the equilibrium current is analyzed under different external power supply conditions. A method of reducing the equilibrium current is proposed, and the voltage loss of the traction substation caused by this method is solved. Next, the electrical performances of traction power supply system are analyzed, including current distribution, impedance and voltage loss. Finally, the model of bilateral power supply system was built, and the theoretical analysis was simulated and verified by Matlab/Simulink.

Development of a technique of simulating railway electric power supply system modes equipped with devices for improving the electrical energy quality in networks powering stationary railway transport facilities. Two structural concepts were considered that provided unbalance reduction and voltage deviations on 0,4 kV buses of substations powering these facilities. The first one was based on the use of negative boosting transformers, and the second one - on the use of lines with an electrically grounded live wire. Two methods of connecting these transformers were considered: into insulated rail joints and into the return wire. The studies were carried out using the Fazonord software package ensuring complex simulation of the modes of railway power supply systems in phase coordinates. To determine the influence of negative boosting transformers and lines with the grounded live wire on the electrical energy quality indicators, an intersubstation zone of the traction network of a double-track 25 kV alternating current railway road with a length of 45 km is considered. The results obtained allowed drawing the following conclusions: when using negative boosting transformers that were connected to the rail break, the average value of the reverse sequence unbalance factor on the 0,4 kV buses of the facility substation was reduced by 2,5% in comparison with the absence of these devices; in the presence of transformers connected to the return wire, this indicator decreased by 19%. The use of line with the grounded live wire instead of a "two wires - rail" line allowed obtaining the electrical energy quality on the 0,4 kV buses. With that, the maximum of the reverse sequence unbalance factor was reduced by 40%. On the basis of computer simulation, it was shown that the use of negative boosting transformers with the return wire and 25kV lines with the grounded live wire makes it possible to improve the electrical energy quality in the systems of the electric power supply of stationary railway transport facilities.

China's high-speed railway adopts a single-phase AC power supply system. In order to balance the three-phase load on the grid side, the railway traction power supply system sets up a phase-separated area every 30km for commutation power supply. At present, most of the phase-separated areas of China's railways use automatic power-off and over-power phase mode. Before the train enters the neutral section, it will receive a signal to automatically disconnect the on-board circuit breaker to cut off the connection between the catenary and the train load. When the train passes through the articulated electrical phase separation, after on-site observation, the voltage drop between the pantograph and the catenary will break down the air when the pantograph slides on the neutral line and begins to gradually separate from the left branch catenary, resulting in repeatedly burning pantograph arcs. Since the on-board circuit breaker has been opened, the high-voltage cables on the train have no load current. The current through the arc in this process can only come from the stray capacitance of the neutral line, the voltage transformer on the high-voltage side of the train, the on-board cables to the car body and so on, this arc current will cause the overvoltage of the catenary. Combined with the Mayr arc model and the Cassie arc model, an improved Habedank arc correction model was built, and the distributed parameter line model of the traction power supply system and the pantograph-catenary multiple arcing model were jointly established. The influencing factors of split-phase overvoltage are derived from the multiple transient processes of the circuit caused by repeated arcing, and the variation law of split-phase overvoltage is obtained.

In the modern world, the efficient use of energy is an extremely important aspect of human activity. In particular, heat supply systems have significant economic, environmental and social importance for both heat consumers and heat supply organizations. The economic status of all participants in the heat supply process depends on the efficiency of the functioning of the heat supply-systems. The reliability of the functioning of systems depends on vital processes such as the work of hospitals and industrial enterprises. With such a close network communication, reliable and efficient operation of power supply systems is critical. In this article, ways to improve the efficiency of heat supply systems are considered. A mathematical model for improved planning of heat supply systems by connecting the optimal set of new heat consumers is presented. For each single customer, when there is an alternative option for connecting this consumer to the existing heat network, it is possible to choose the only optimal solution. This becomes possible due to the restrictions and the procedure for selecting variants from a subset of binary variables corresponding to alternatives. The procedure for finding the optimal number of consumers for connection to the existing heat network is presented, which is the rationale for increasing the number of existing consumers of the heat network. The testing was carried out and the results of the mathematical model by an example of test heat networks are presented. Directions of further study of increasing the efficiency of heat supply systems and integrating the presented mathematical model with modern software complexes are determined.

In the modern world, the efficient use of energy is an extremely important aspect of human activity. In particular, heat supply systems have significant economic, environmental and social importance for both heat consumers and heat supply organizations. The economic status of all participants in the heat supply process depends on the efficiency of the functioning of the heat supply systems. The reliability of the functioning of systems depends on vital processes such as the work of hospitals and industrial enterprises. With such a close network communication, reliable and efficient operation of power supply systems is critical. In this article, ways to improve the efficiency of heat supply systems are considered. A mathematical model for improved planning of heat supply systems by connecting the optimal set of new heat consumers is presented. For each single customer, when there is an alternative option for connecting this consumer to the existing heat network, it is possible to choose the only optimal solution. This becomes possible due to the restrictions and the procedure for selecting variants from a subset of binary variables corresponding to alternatives. The procedure for finding the optimal number of consumers for connection to the existing heat network is presented, which is the rationale for increasing the number of existing consumers of the heat network. The testing was carried out and the results of the mathematical model by an example of test heat networks are presented. Directions of further study of increasing the efficiency of heat supply systems and integrating the presented mathematical model with modern software complexes are determined.

Problematics. In the conditions of objectively existing aging of electric equipment, climatic conditions deterioration, hard work schedule of operation personnel at modern EES of NPS, there grows the problem of ensuring reliability and safety of functioning of the NPS in the emergencies in a power supply system. That requires carrying out the complex risk analysis of EES subsystems and NPS operation in the case of refusal of electrical equipment. Research objective . Development of mathematical support and software for assessment of circuits reliability and refusal risk of NPS MV external power supply system under conditions of internal MV power supply loss for providing the mode of shut-down cooling and cold start of the block. Implementing procedure. In the condition of essential incompleteness and uncertainty of statistical information on refusals of external network electric equipment, the hybrid fuzzy-stochastic models of certain electrical equipment failure for an assessment of refusal risk of NPP MV external power source method of electrical equipment failure function of distribution is attached. It is based on use of statistical data on refusals of main population of certain type and voltage class electric equipment as well as the expert estimates of refusal intensity of certain units of equipment. Results of research. The hybrid fuzzy-stochastic models of refusals of the main power and switching equipment of power supply systems and own needs of the NPS and fuzzy-stochastic models of refusal risk assessment of MV external power supply system are developed. The probability assessment of no-failure operation and fuzzy ranging on reliability is carried out for four versions of power supply circuits of the NPS HV distributing device; the refusal risk assessment of the external power supply system from remote power plants and substations is executed. Conclusions. In order to estimate schemes reliability and risk failure of electrical equipment and system of power supply MV from external supplies, fuzzy mathematical models were developed and failure risk estimation of four power supplies schemes for high-voltage NPS highways.

There is the risk of subsynchronous oscillations when wind-thermal-bundled power supply delivered through AC transmission line with series capacitance compensation and high voltage DC system. However, the current researches are all aimed at the subsynchronous oscillation of wind-thermal-bundled power supply or AC-DC hybrid transmission, without considering the subsynchronous oscillation of wind farms, thermal power plants, AC transmission system with series capacitance compensation and DC transmission system at the same time. The linearized model of wind-thermal power supply and extreme high voltage (EHV) AC-DC hybrid transmission system is built firstly in this paper and then subsynchronous oscillation mode of system is analyzed by factors related with characteristic values. This study uses characteristic values sensitivity make sure the main influencing factors of subsynchronous oscillation and then analyze the influence of AC-DC transmission power distribution, thermal power and wind power output allocation, wind power control parameters and DC transmission control parameters on subsynchronous oscillation. The correctness of theoretical analysis is verified by the simulation results.1

The power supply systems of the agro-industrial complex are full with electrical equipment that requires a supply voltage corresponding to GOST for normal operation. Operating modes caused by the nonlinear load have a negative impact on the operation of power electrical equipment, relay protections, automation elements and switching devices. Additional power losses associated with higher current harmonics appear during operation of all types of electric motors and in electrical installations in conditions of non-sinusoidal voltage. The technical parameters of the operation of electrical equipment, as well as the quantitative and qualitative properties of the products largely depend on the quality of electrical energy in the electrical supply systems of enterprises of the agro-industrial sector. The correct use of methods and means of improving the quality of electric energy will allow us to calculate more accurately the economic damage from non-sinusoidal and asymmetric operating modes. These conditions should be taken into account when designing and operating power supply systems. The need to determine the damage arises during the development and adjustment of standard documents on the quality of electricity when justifying the limit values of the quality indicators. (Research purpose) The research purpose is studying the influence of higher harmonics on the operating modes of electrical equipment in rural distribution networks. (Materials and methods) The article presents the main sources of voltage distortion, calculations on power losses in distribution grids of agricultural consumers. (Results and discussion) The article presents the results of measuring the non-sinusoidal voltage in the distribution grids of agricultural enterprises. The coefficients of the harmonic components in the voltage harmonics spectrum is higher than it should be. (Conclusions) The losses associated with the low quality of the supply voltage caused by electromagnetic and technological components.