Ferroresonance Elimination in 275kV Substation

Abstract This work studies the non-conventional ferroresonance oscillation in the 275kV substation. Voltage transformer (VT) which is used in this substation has a 100VA capacity and magnetization characteristic of it was modeled by single-value two-term polynomial with q=7. In this study, at first ferroresonance oscillation in VT has been introduced, then effect of Metal Oxide Varistor (MOV) on limiting these nonlinear overvoltages is investigated. It has been shown for some parameters values, MOV cannot control the ferroresonance. So, by connecting the neutral earth resistance (NR) to the system grounding, non-conventional oscillation has been controlled for all value of system parameters. Simulation results show that considering neutral earth resistance exhibit great controlling of ferroresonance overvoltages. It is also shows by using this resistance, system exhibit less sensitivity to the changing the parameters value of the power system

Ferroresonance Suppression in Power Transformers using Chaos Theory

a b s t r a c t The main goal of this paper is the determination of the effect of the metal oxide varistor (MOV) on various ferroresonance modes including fundamental resonance, subharmonic and chaos mode which are generated in electrical power systems. Chaos theory is used for analyzing this effect. Also, the bifurcation, phase plan diagram and time domain simulation are used for this purpose. The proposed power system contains a no-load or lightly loaded power transformer. The magnetization curve of the transformer core is modeled by a single-value two-term polynomial. The core loss is modeled based on the flux of the transformer. The MOV modeled as a nonlinear voltage dependent resistance. The suppression effect of MOV on chaotic ferroresonance in power transformer is studied in this paper. The simulation results confirm that connecting the MOV to the transformer has a considerable suppression effect on ferroresonance phenomena

Fast AC reactor-based fault current limiters application in distribution network

Almost all of the fault current limiters (FCLs) have a negligible voltage drop during normal operation mode of the power system and show considerable impedance during the fault period. In addition, the most of the FCLs employ a reactor to limit the fault current, which carrying a DC current and named DC reactor-based FCL (DRFCL) or carrying AC current named AC reactor-based FCL (ARFCL). Here, a novel ARFCL is introduced for radial distribution networks protection. Then, the ARFCL performance on the limitation of the fault current is compared with DRFCL in a simple radial distribution network. The MATLAB software is used to simulate both FCLs performance and their effect on the fault current. The laboratory prototype of the ARFCL is built and tested for the evaluation of the ARFCL performance during normal and fault operation modes. The simulation and experimental results show the superiority of ARFCL to control the fault current, fast, and set the point of common coupling voltage in an acceptable range

Stabilizing Ferroresonance Oscillations in Voltage Transformers Using Limiter Circuit

This paper employs the multiple scales method and chaos theory for analyzing chaotic behavior of the voltage transformer (VT) with linear core loss model. It is shown that ferroresonance phenomenon in VTs can be classified as chaotic dynamics, including a sequence of bifurcations such as period doubling  bifurcation  (PDB),  saddle  node  bifurcation  (SNB),  Hopf  Bifurcation  (HB)  and chaos. Bifurcation diagrams and phase plane diagrams are drawn using a continuation method for linear core loss model and lyapunov exponents are obtained using the multiple scales method. At first an overview of the subject in the literature is provided. Then, ferroresonance phenomenon is introduced and its various types in a VT are simulated. Finally the effects of ferroresonance suppression circuit on stabilizing these oscillations are studied. The proposed approach is implemented using MATLAB, and simulation results are presented. The results show connecting the ferroresonance suppression circuit to the system configuration, causes great controlling effect on ferroresonance overvoltage

Modeling and evaluation of technical, economical and environmental performance of molten carbonate fuel cell compared to micro turbine gas for the production of electricity and heat simultaneously

Given the increased consumption and energy costs, the reduction of fossil fuels and the growing concern for environmental issues and global warming, finding a way to convert energy with high efficiency and low environmental impact is essential. The purpose of this study is to model and evaluate the technical, economical and environmental aspects of the molten carbonate fuel cell compared to the conventional technology of micro turbine gas. According to the estimates made in various capacities, the fuel efficiency of the fuel cell was 23% higher than that of the micro turbine, which would reduce fuel consumption in the fuel cell. In terms of the environment, the amount of carbon dioxide produced in a fuel cell and micro turbine is 377 and 625 grams per kilowatt-hour, which represents 40% lower emissions in fuel cells. In the economic evaluation, various parameters such as carbon taxes, fuel prices and fuel cell stack costs are very influential. According to forecasts, with increasing carbon taxes in the coming years and lowering the cost of fuel cell technology, this technology can be exploited by conventional power generation technologies such as gas micro turbines

Circuit breakers in HVDC systems: state-of-the-art review and future trends

Abstract High voltage direct current (HVDC) systems are efficient solutions for the integration of large-scale renewable energy sources with the main power grids. The rapid development of the HVDC grid has resulted in a growing interest in DC circuit breakers (DCCBs). A fast and reliable circuit breaker is a necessary requirement in the development of large scale HVDC grids. This paper provides a comprehensive review and survey of the HVDC CBs and discusses potential research directions. Operational principles and the main features of various DCCBs are described and their merits and shortcomings are also highlighted