Long-distance Power Transmission Lines Research Articles

Enhancing of the power system resilience through the application of micro power systems (microgrid) with renewable distributed generation

The power sector plays a critical role in the functioning of the economy and the security of a country, being closely interconnected with other vital infrastructures, such as gas supply, water supply, transportation, and telecommunications. Ensuring a stable power supply is crucial for the uninterrupted operation of these systems. One way to enhance the resilience of the power system is by integrating local networks with distributed renewable generation into the overall energy infrastructure. The flexibility, stability, controllability, and self-healing capabilities of microgrids make them an effective solution for improving the resilience of the power system. The power grid is susceptible to disturbances and disruptions that can cause large-scale power outages for consumers. Statistical data indicates that approximately 90% of outages occur due to issues in the distribution system, thus research focuses on local microgrids with distributed renewable generation. This study analyzed the role of microgrids with renewable generation in enhancing the resilience of power systems. Additionally, functions of microgrids that contribute to enhancing power system resilience, such as service restoration, network formation strategies, control and stability, as well as preventive measures, were summarized. It was found that local microgrids have significant potential to enhance power system resilience through the implementation of various strategies, from emergency response planning to providing reliable energy supply for quick responses to military, environmental, and human-induced crises. The concept of local distributed energy generation, storage, and control can reduce reliance on long-distance power transmission lines, reduce network vulnerabilities, and simultaneously improve its resilience and reduce recovery time. It has been determined that the most necessary and promising approaches to enhance the resilience of the power system include developing appropriate regulatory frameworks, implementing automatic frequency and power control systems, ensuring resource adequacy (including the reservation of technical components), promoting distributed generation, integrating energy storage systems into the energy grid, and strengthening cyber security. Keywords: resilience, local power systems, MicroGrid, distributed generation, renewable energy sources.

Aperiodic steady-state stability criterion of electric power system with controlled series compensation on 200 kV line

Currently there is a need to synchronize operation of the electric power system in the remote areas and increase of existing lines transmission capacity. The construction of new power transmission lines involves high economic expenditures. Well-known papers consider the issues of application of controlled series compensation devices only for long-distance power transmission lines with voltage of 500 kV and higher to increase the transmission capacity and the level of stability. The aim of the study is to increase the stability and the limit of the transmitted power when controlled series compensation devices are installed on 220 kV lines. It is necessary to develop a criterion of aperiodic steady-state stability of an electric power system with a 220 kV-controlled power transmission line. Methods of mathematical modeling of electric power system, the theory of long-distance power transmission lines and electromechanical transients, and methods of analyzing electric power system stability were used. A.M. Lyapunov’s first approximation method was used to develop a simplified mathematical model. We applied the developed software as a simulation tool. An analysis was carried out to study the influence of series compensation devices regulation coefficients on the aperiodic steady-state stability of the electric power system and the transmission capacity of 220 kV power transmission lines. A change in the modulus of voltage drop at the power transmission and the angle characteristics under the influence of the regulation coefficients of the series compensation device was revealed. A criterion of aperiodic steady-state stability has been developed for systems of this kind with controlled series compensation. It differs from traditional ones by considering the changes in the voltage drop in the power transmission and it allows more accurate estimation of the proximity to the stability threshold. An assessment of aperiodic steady-state stability according to the formulated criterion for an electric power system with a controlled series compensation device on a 220 kV line was obtained. The values of the control coefficients of the series compensation device have been determined. No violation of the steady-state stability occurs under the given values. The results can be used to solve the issues of increasing the transmission capacity of transmission lines to improve the stability of the system.

An improved fault current limiting circuit for VSC-HVDC transmission system

In order to maximize the utility of renewable energy resources, long-distance power transmission lines are essentially required. To accomplish this purpose, the voltage-source-converter (VSC) based high voltage direct current (HVDC) transmission is considered an attractive option. However, due to DC-link capacitors and their discharge currents, the VSC-HVDC based transmission networks are more vulnerable to short circuit faults. The direct current circuit-breakers (DCCBs) are considered a reliable option to protect the transmission line against short circuit faults. The DCCBs with increased voltage rating and fault-current interruption capability are still considered a gigantic problem. The capacity issues of DCCBs can be alleviated using some external circuits to reduce the intensity of fault-current. This paper introduces an external fault-current limiting circuit (FCLC), which is non-superconducting in nature, and it consists of power electronics-based bidirectional switches, current limiting inductor, and power dissipating resistor. This circuit is placed in series with a DCCB, to escalate the response time in the advent of fault, to restrict the maximum value of fault-current, and to reduce the stresses on energy absorption components in DCCB. The circuit is activated only when fault-current limitation operation is required, thereby, the proposed FCLC has zero power-loss in the nonoperational state, and has no influence on the steady-state performance of the system. Furthermore, regarding FCLC, the detailed working principle, parametric analysis, and rigorous evaluation of performance are accomplished in this paper. The theoretical concepts are validated using a three-terminal VSC-HVDC model and equivalent circuit analysis, in PSCAD/EMTDC simulation-based environment. The results of FCLC are compared with other solutions in the literature. The comparison of results concludes that the proposed FCLC own better characteristics, in terms of control features, fault clearing time, and power losses.

Asian international grid connection and potentiality of DC superconducting power transmission

In 2011, a large scale earthquake and tsunami hit the northeastern coast of Japan, and nuclear plants were damaged to a large extent. Before the Tsunami, 54 nuclear plants were operated, however presently, only three nuclear plants are in operation. Therefore, Japan is suffering from high price of electricity and low supply reliability. In generation mix, nuclear plants generate only one percent and 87 percent of electricity is generated by fossil energy. This is not preferable for Japan from the viewpoints of energy security and stable electricity supply. Therefore, it is mandatory to increase sustainable energy and to decrease consumption of fossil fuel. International grid connection and the Global Energy Interconnection will be one of countermeasures against these problems existing in Japan. In this paper, international grid connection initiatives proposed in Asia are described and features and issues of electric power grids in Japan are discussed to implement the international grid connection. As the key technology for implementing the international grid connection, the present status of DC superconducting power transmission lines and power converters for long-distance power transmission lines are presented. In conclusion, conditions and legal frameworks for realizing the international grid connection are described.

Operative optimization of normal modes of non-uniformity electric networks with long-distance power transmissions

An improved mathematical model of the non-uniformity of the electrical system (ES) with the long-distance AC power transmission was presented. A method of forming the control actions for the control devices of such system, the implementation of which allows to ensure maximum power transmission efficiency was proposed. The features of the hardware and software implementation of local management of ES control devices, which provides the benefits of centralized management were given. Electrical systems are not optimal in terms of electricity consumption in its production, transportation and distribution. One of the main reasons for non-optimal states of the ES is their non-uniformity. Based on the above mathematical model of non-uniformity of electric networks taking into account the operation features of long-distance power transmission lines it was shown that for such networks because of the instability of the longitudinal and transverse parameters, their uniform state cannot be practically achieved. Thus, ensuring the optimality of their modes requires using appropriate automatic control systems. To solve the problem of determining the optimal control laws of ES coupling transformers taking into account the features of their impact on the process of electricity transmission and distribution in electric networks with long-distance power transmissions, a mathematical model of optimal electromotive forces of imbalance, as well as the method of determining the optimal transformation ratios of control devices taking into account the wave properties of long-distance PTL, as well as the effect of unbalanced ratios of transformation of coupling transformers and voltage regulation in ES power centers, were proposed. This improvement allows to make better decisions in the optimal control of power flows and voltage in the ES.

Numbers and Number Systems

Every intelligent person has a background which includes experiences with numbers. These experiences go back to preschool days. A person learns to count before he learns to read. His concept of number grows from a concept which includes only the counting numbers to one which includes fractions, decimals, irrationals, and perhaps negative numbers and complex numbers. These are the numbers of elementary mathematics. These are the numbers of science and of business. These are the numbers of a world equipped with electronic computers, long-distance power-transmission lines, dial telephones, guided missiles, and space satellites. Everyone takes numbers for granted. Everyone uses numbers as tools. Everyone has a number sense, an intuition about numbers and their relationships. But not everyone has spent time thinking about the nature of numbers. Our purpose in this paper is to focus primary attention upon numbers as objects of deliberate mature thought. We outline briefly the development of the number concept and the organization of numbers into number systems. We hope to stimulate the reader, to help him organize his past number experiences and perhaps help him to see something new and exciting about numbers. A system of numbers consists of a set or collection of numbers and one or more operations for combining the numbers of the system. The numbers of the system sometimes are called the elements of the system. The system of counting numbers consists of the elements 1, 2, 3, * ?, and the fundamental operations (addition, subtraction, multiplication, and division) for combining tnem. The symbol 1, 2, 3, .., suggests that there are an infinite number of elements; it also suggests that they have a natural order. This is the order in which they are used as counters, Following the natural number 1 is the natural number 2; 2 is sometimes called the successorofi. Then 2 is followed by 3, 3 is followed by 4, and so on; 9isfollowed by 10, 10 by 11, and so on; 1957 by 1958, and so on, ad infinitum. Although all of the natural numbers have never been written in symbols, they have been conceived, at least in a collective sense, as objects of thought. Natural numbers developed as a sequence of distinguishable grunts or marks which the prehistoric man employed to see if his prehistoric dog had brought in all of his prehistoric sheep. These are the natural numbers

A miniature A-C. transmission system: For the practical solution of network and transmission-system problems

The use of so-called “artificial lines” — i.e. miniature models of electric circuits — for experimental laboratory studies of transmission-line phenomena is well known. The miniature models are commonly made so as to represent, in true proportion, the electrical constants of a real line. Thus there are artificial telephone lines, artificial submarine cables, artificial long-distance power-transmission lines, etc. A miniature line is a true model of a real line to the extent that the miniature circuit has, for any desired degree of approximation, the same electrical behavior as the full-size circuit. Such laboratory models frequently permit — far more conveniently than the full-size circuit — the study of actual circuit phenomena in a practical and efficient manner. When their limitations are properly understood, miniature circuits may be of great value to transmission-line and operating engineers. Miniature electric circuits may for the present purpose be divided into two general classes: (1) Miniature circuits intended for the study of problems on long lines, such as lines having continuously distributed circuit constants. (2) Miniature circuits for the solution of problems involving complete system networks, inclusive of generating-station and substation apparatus. The following paper deals with a three-phase miniature a-c. system of the network type. The circuit includes synchronous machines, transformers, adjustable resistors, reactors, and condensers, for complete representation of generating stations, substations, lines and loads. The circuit connections are variable, so that any system having not more than the available number of circuit elements may be represented for the correct experimental solution of low-frequency problems. This miniature system has so far given about three years of service in the experimental analysis of transmission system behavior, for existing systems and for systems to be constructed. The problems solved have been within the realms of both the designing and the operating engineers, and have been applied to power systems in this country as well as abroad. One of the by-products of the miniature system is the confirmation and extension of the theory of transmission-line phenomena. Several prominent engineers have expressed the belief, and made the prediction, that after a few years of proper use of the miniature system, the theory and calculation of the present transmission problems will have been so well established that experimental solutions will no longer be necessary. In this paper are given (1) a brief discussion of some of the present problems calling for solutions by the miniature experimental method, (2) a full description of the miniature equipment, (3) an outline of the operating procedure in the solution of problems, and (4) an example illustrating the application of the miniature equipment.

A Miniature A-C. Transmission System For the Practical Solution of Network and Transmission-System Problems

The use of so-called “artificial lines” — i.e. miniature models of electric circuits — for experimental laboratory studies of transmission-line phenomena is well known. The miniature models are commonly made so as to represent, in true proportion, the electrical constants of a real line. Thus there are artificial telephone lines, artificial submarine cables, artificial long-distance power-transmission lines, etc. A miniature line is a true model of a real line to the extent that the miniature circuit has, for any desired degree of approximation, the same electrical behavior as the full-size circuit. Such laboratory models frequently permit — far more conveniently than the full-size circuit — the study of actual circuit phenomena in a practical and efficient manner. When their limitations are properly understood, miniature circuits may be of great value to transmission-line and operating engineers. Miniature electric circuits may for the present purpose be divided into two general classes: (1) Miniature circuits intended for the study of problems on long lines, such as lines having continuously distributed circuit constants. (2) Miniature circuits for the solution of problems involving complete system networks, inclusive of generating-station and substation apparatus. The following paper deals with a three-phase miniature a-c. system of the network type. The circuit includes synchronous machines, transformers, adjustable resistors, reactors, and condensers, for complete representation of generating stations, substations, lines and loads. The circuit connections are variable, so that any system having not more than the available number of circuit elements may be represented for the correct experimental solution of low-frequency problems. This miniature system has so far given about three years of service in the experimental analysis of transmission system behavior, for existing systems and for systems to be constructed. The problems solved have been within the realms of both the designing and the operating engineers, and have been applied to power systems in this country as well as abroad. One of the by-products of the miniature system is the confirmation and extension of the theory of transmission-line phenomena. Several prominent engineers have expressed the belief, and made the prediction, that after a few years of proper use of the miniature system, the theory and calculation of the present transmission problems will have been so well established that experimental solutions will no longer be necessary. In this paper are given (1) a brief discussion of some of the present problems calling for solutions by the miniature experimental method, (2) a full description of the miniature equipment, (3) an outline of the operating procedure in the solution of problems, and (4) an example illustrating the application of the miniature equipment.