A Study of Superconducting Transformer with Short-Circuit Current Limitation

The paper presents physico-mathematical models for analyzing transient processes in electrical networks having transformers with a high temperature superconducting winding. One of the main purposes of the study is the investigation of the short circuit current limitation process with the use of a transformer with a high temperature superconducting winding, that allows the combination of two series-connected elements, transformer and reactor, in one device. The efficiency of this method for short circuit current limitation is provided by the fact that the critical value of superconducting winding temperature is exceeded under short circuit current flowing, then it passes into the normal state with a high impedance winding, thus limiting a short circuit current. It is important to know the moment when superconducting material passes into the normal state with the loss of superconductivity. For this purpose, the program for calculating the quantity of heat under short circuit current flowing before its interruption was developed. If a 40 MVA transformer with a high temperature superconducting winding is considered, short circuit should be cleared after 100 ms without transformer disconnection. It is proposed to use a hybrid winding in addition to the main winding for short circuit current limitation. Conducted investigations showed that the return of a winding into the superconducting state depends primarily on the ratio between a short circuit current and a rated load current. This represents the criterion for returning or not returning into the superconducting state for transformer windings

Swarm algorithms in dynamic optimization problem of reactive power compensation units control

Optimization of a power supply system is one of the main directions in power engineering research. The reactive power compensation reduces active power losses in transmission lines. In general, researches devoted to allocation and control of the compensation units consider this issue as a static optimization problem. However, it is dynamic and stochastic optimization problem that requires a real-time solution. To solve the dynamic optimization NP-hard problem, it is advisable to use Swarm Intelligence. This research deals with the problem of the compensation units power control as a dynamic optimization problem, considering the possible stochastic failures of the compensation units. The Particle Swarm Optimization and the Bees Algorithm were applied to solve it to compare the effectiveness of these algorithms in the dynamic optimization of a power supply system

Modeling and Experimental Study of the Inrush Current of a High-Temperature Superconducting Transformer

Inrush current in high-temperature superconducting (HTS) transformers is a little-studied phenomenon. After connecting to the power grid, a current flow through the windings which exceeding the critical current value of the superconducting tape. It may cause significant overheating and thermal damage of winding. The purpose of the study is to develop a mathematical model for calculating inrush current pulses in a HTS transformer and its verification by physical experiments. To achieve the goal of the study, a mathematical model has been developed that accurately represents the electromagnetic and thermal transient processes after HTS transformer is turned on at idling or under load. The model considers the critical parameters of the HTS tapes, the process of heating and cooling of the windings, quench characteristics, and the electrical and magnetic parameters of the transformer. Good compliance of the experimental results and mathematical modeling with a deviation of 1.99 % allowed us to verify the model. The most important result is the creation of a mathematical model of the HTS transformer at the moment of connecting to power grid. This model represents the temperature changing of the windings during the loss of superconductivity. The developed model can be used in the analysis and modeling of inrush current in designed and operating HTS transformers for any power. The obtained results are significant for determine the optimal starting characteristics, geometric and electrical parameters of HTS transformers. The proposed methods for reducing the inrush current ensure safe and reliable operation of the HTS transformer when switched on at idling or under load

The Construction of Holonic Infrastructure of Intelligent Networks in the Smart Grid Concept with a Two-Way Flow of Energy

The paper deals with the intelligent network modes based on the Smart Grid concept with the function of two-way energy flow, both from the power system and from its sources of distributed generation. The expanded interpretation and the meaning of the intellectual network concept - Smart Grid - is proposed, based on its abbreviation, which determines the system criteria for its purpose. A new concept is introduced and new definition - Holonic Approach - Smart Grid concept. A new term has been introduced: - "Generating Consumer-Holon" (GC-Holon), which means the ability of an electric consumer to independently generate energy using renewable sources, store it, exchange energy with other similar GC-Holon and the main generating system. In connection with this, the concept of a generating consumer has been introduced. To construct an intelligent network, a holonic structure based on a set of holons (subsystems) is used. The holonic structure assumes subsystems of different nature, located at different levels of aggregation, interconnected in order to form a hierarchy of self-regulating holons, called Holarchy. According to A. Koestler, holons are simultaneously, both whole and partial. They are basically autonomous, which allows them to ensure their existence independently. The two-way energy flow for the holonic structure assumes the possibility of generation and storage of energy due to the internal structure of the electric consumer. The infrastructure of an intelligent network and its applications are considered. A mathematical model of bilateral electric power consumption by a generating consumer is proposed, taking into account tariffs and pricing. This allows you to flexibly regulate energy flow and align the load schedule, minimizing financial expenses for consumed energy

Study of Electromagnetic and Thermal Transients in a High-temperature Superconducting Transformer during a Short Circuit

Today, high-temperature superconducting (HTS) current limiters and transformers allow to limit the surge short circuit current during failure without negatively affecting on the power grid com-plex at the normal operation mode. However, the transition of a superconductor to a resistive state at the moment of current limitation can cause significant heat generation, which can destroy the transformer windings. The research goal is to provide optimal technical characteristics of the HTS transformer to achieve effective short circuit current limitation and prevent thermal breakdown of its windings. To achieve this goal, a mathematical model of a HTS transformer was developed. The presented method considers the material type and geometry of the superconducting tape, the critical parameters of the superconductor (current and temperature), the parameters of the cryogenic liquid, dependence of the resistance and heat capacity of the HTS tape layers on temperature. The simulation model was created in the Matlab/Simulink software. The most important result is the possibility of obtaining optimal elec-trical and thermal parameters of the HTS transformer windings during the short circuit current limitation, as well as ensuring the thermal stability of the superconducting tape at the quench moment. The obtained results are significant in the design and operation of HTS transformers. For efficient and safe operation in the current-limiting mode, it is necessary to take into account heat generation on the transformer windings. It is important for the superconductor returning to the superconducting state without causing significant overheating of the windings

Increase of the Integration Degree of Wind Power Plants into the Energy System Using Wind Forecasting and Power Consumption Predictor Models by Transmission System Operator

Wind power plants’ (WPPs) high penetration into the power system leads to various inconveniences in the work of system operators. This fact is associated with the unpredictable nature of wind speed and generated power, respectively. Due to these factors, such source of electricity must be connected to the power system to avoid detrimental effects on the stability and quality of electricity. The power generated by the WPPs is not regulated by the system operator. Accurate forecasting of wind speed and power, as well as power load can solve this problem, thereby making a significant contribution to improving the power supply systems reliability. The article presents a mathematical model for the wind speed prediction, which is based on autoregression and fuzzy logic derivation of Takagi-Sugeno. The new model of wavelet transform has been developed, which makes it possible to include unnecessary noise from the model, as well as to reveal the cycling of the processes and their trend. It has been proved, that the proposed combination of methods can be used simultaneously to predict the power consumption and the wind power plant potential power at any time interval, depending on the planning horizon. The proposed models support a new scientific concept for the predictive control system of wind power stations and increase their degree integration into the electric power system