Ferroresonance in the High Voltage Powerline Industry

Ferroresonance is an issue often overlooked in the high voltage powerline industry. Ferroresonance is a complex nonlinear electrical phenomenon that can cause dielectric and thermal problems to transformers. It is a very complex topic that is not completely understood and requires a large amount of work in order to comprehend. It can cause injury to Lineman that work around it and damage equipment. The proper training and a safety device could make the industry safer and save money. Through interviews and research I have studied the need for a safety device that applies load to a transformer during installation in order to eliminate the risk of Ferroresonance. I have also developed a prototype that can be used to apply 20 amps of load at 120V to the secondary side of a transformer. A product like this could be very valuable to have in the industry

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 simulation studies of transmission systems

The onset of a ferroresonance phenomenon in power systems is commonly caused by the reconfiguration of a circuit into the one consisting of capacitances in series and interacting with transformers. The reconfiguration can be due to switching operations of de-energisation or the occurrence of a fault. Sustained ferroresonance without immediate mitigation measures can cause the transformers to stay in a state of saturation leading to excessive flux migrating to transformer tanks via internal accessories. The symptom of such an event can be unwanted humming noises being generated but the real threatening implication is the possible overheating which can result in premature ageing and failures.The main objective of this thesis is to determine the accurate models for transformers, transmission lines, circuit breakers and cables under transient studies, particularly for ferroresonance. The modeling accuracy is validated on a particular 400/275 kV transmission system by comparing the field test recorded voltage and current waveforms with the simulation results obtained using the models. In addition, a second case study involving another 400/275 kV transmission system with two transformers is performed to investigate the likelihood of the occurrence of sustained fundamental frequency ferroresonance mode and a possible quenching mechanism using the 13 kV tertiary connected reactor. A sensitivity study on transmission line lengths was also carriedout to determine the probability function of occurrence of various ferroresonance modes. To reproduce the sustained fundamental and the subharmonic ferroresonance modes, the simulation studies revealed that three main power system components which are involved in ferroresonance, i.e. the circuit breaker, the transmission line and the transformer, can be modeled using time-controlled switch, the PI, Bergeron or Marti line model, and the BCTRAN+ or HYBRID transformer model. Any combination of the above component models can be employed to accurately simulate the ferroresonance system circuit. Simulation studies also revealed that the key circuit parameter to initiate transformer ferroresonance in a transmission system is the circuit-to-circuit capacitance of a double-circuit overhead line. The extensive simulation studies also suggested that the ferroresonance phenomena are far more complex and sensitive to the minor changes of system parameters and circuit breaker operations. Adding with the non-linearity of transformer core characteristics, repeatability is not always guaranteed for simulation and experimental studies. All simulation studies are carried out using an electromagnetic transient program, called ATPDraw.EThOS - Electronic Theses Online ServiceBrunei GovernmentGBUnited Kingdo

Comparative Analysis of Numerically Computed Chaos Diagrams in Duffing Oscillator

Abstract This study utilised optimum fractal disk dimension algorithms to characterize the evolved strange attractor (Poincare section) when adaptive time steps Runge-Kutta fourth and fifth order algorithms are employed to compute simultaneously multiple trajectories of a harmonically excited Duffing oscillator from very close initial conditions. The challenges of insufficient literature that explore chaos diagrams as visual aids in dynamics characterization strongly motivate this study. The object of this study is to enable visual comparison of the chaos diagrams in the excitation amplitude versus frequency plane. The chaos diagrams obtained at two different damp coefficient levels conforms generally in trend to literature results[1] and qualitatively the same for all algorithms. The chances of chaotic behaviour are higher for combined higher excitation frequencies and amplitudes in addition to smaller damp coefficient. Fourth and fifth order Runge-Kutta algorithms indicates respectively 62.3% and 53.3% probability of chaotic behaviour at 0.168 damp coefficient and respectively 77.9% and 78.9% at 0.0168 damp coefficient. The chaos diagrams obtained by fourth order algorithms is accepted to be more reliable than its fifth order counterpart, its utility as tool for searching possible regions of parameter space where chaotic behaviour/motion exist may require additional dynamic behaviour tests

Prognostic Approaches Using Transient Monitoring Methods

The utilization of steady state monitoring techniques has become an established means of providing diagnostic and prognostic information regarding both systems and equipment. However, steady state data is not the only, or in some cases, even the best source of information regarding the health and state of a system. Transient data has largely been overlooked as a source of system information due to the additional complexity in analyzing these types of signals. The development for algorithms and techniques to quickly, and intuitively develop generic quantification of deviations a transient signal towards the goal of prognostic predictions has until now, largely been overlooked. By quantifying and trending these shifts, an accurate measure of system heath can be established and utilized by prognostic algorithms. In fact, for some systems the elevated stress levels during transients can provide better, more clear indications of system health than those derived from steady state monitoring. This research is based on the hypothesis that equipment health signals for some failure modes are stronger during transient conditions than during steady-state because transient conditions (e.g. start-up) place greater stress on the equipment for these failure modes. From this it follows that these signals related to the system or equipment health would display more prominent indications of abnormality if one were to know the proper means to identify them. This project seeks to develop methods and conceptual models to monitor transient signals for equipment health. The purpose of this research is to assess if monitoring of transient signals could provide alternate or better indicators of incipient equipment failure prior to steady state signals. The project is focused on identifying methods, both traditional and novel, suitable to implement and test transient model monitoring in both an useful and intuitive way. By means of these techniques, it is shown that the addition information gathered during transient portions of life can be used to either to augment existing steady-state information, or in cases where such information is unavailable, be used as a primary means of developing prognostic models

Modelling and analysis of electric arc loads using harmonic domain techniques

Abstract It has been reported that as much as 12% of global electricity production goes into producing artificial light using arc discharge lamps and that global annual production of these lamps may be as much as 1.2 billion units. In the liquid steel production industry, one metric tone of steel demands, on average, 400 kW-hr and in the year 2007, the crude steel output reached 1,343.5 million metric tons. In both instances, engineered electric arcs are present and represent major loads in electrical power systems which require the utmost attention. They observe a highly non-linear behaviour with the capacity to export harmonic distortion and flicker into the power system. Electric arc furnace installations, in particular, are well-known to be sources of dynamic disturbances affecting neighbouring loads. Arc discharge lamps, on aggregate, may exhibit the same perturbing effect. Over the years, the non-linear nature of these loads and their ubiquitous nature have caught the interest of researchers in all corners of the world and from different backgrounds, including this author. The research work reported in this thesis advances current knowledge in the modelling and simulation of electric arcs with particular reference to arc discharge lamps with electromagnetic ballasts and electric arc furnaces with particular reference to operational unbalances and the impact in the installation of ancillary power electronics equipment. In these two quite distinct applications, linked by the presence of engineered electric arcs, the fundamental modelling item is a non-linear differential equation which encapsulates the physic of the electric arc by applying power balance principles. The non-linear differential equation uses the arc conductance as state variable and adapts well to model a wide range of characteristics for which a set of experimental coefficients are available. A fact of perhaps equal relevance is that the non-linear differential equation is amenable to algebraic representations using operational matrices and suitable for carrying out periodic steady-state solutions of electric circuits and systems. The modelling and numerical solution takes place in the harmonic space where all harmonics and cross-couplings between harmonics are explicitly represented. Good application examples are the harmonic domain solution of arc discharge lamps with electromagnetic ballasts and the harmonic domain solution of electric arc furnaces with ancillary power electronics equipment. Building on the experience gained with the representation of the arc discharge lamps with electromagnetic ballasts, the research turns to the representation of the electric arc furnace installation with provisions for reactive power compensation using power electronic control and harmonic filters. This is a three-phase application which comprises several nodes, giving rise a large-scale model of a non-linear system which is solved in the direct frequency domain using a blend of the Newton-Raphson method and the Gauss-Seidel method, achieving robust iterative solution to a very tight tolerance. Both algorithms are implemented in MATLAB code and the raw simulation results which are the harmonic complex conjugated vectors of nodal voltages are used to assess in a rather comprehensive manner the harmonic interactions involved in both kinds of applications

Modelling load balance type static var compensator control system response

As power system interconnection becomes more prevalent, there has been an increase in use of thyristor controlled shunt connected compensation devices for dynamic power system compensation and power transmission capacity increase. A Static Var Compensator (SVC) functions as a variable reactance capable of operating in both the inductive and capacitive region as required on a cycle by cycle basis to provide compensation at the point of connection to the power system. Voltage regulation is the operational objective of most SVCs. Therefore, transient response of SVC control systems impacts overall power system performance and inappropriate settings may lead to voltage instability. SVCs are also commonly used to convert single phase load into balanced three phase load, thereby reducing negative phase sequence voltages and currents within the power transmission system. As most load balancing SVCs are consistently operated to their capacity, removal from service to apply and test control system setting changes impacts system regulation and stability. Therefore, model development of a load balancing type SVC control system to predict response to setting changes may provide an alternative to lengthy outages of SVC plant. This paper examines the theoretical basis of thyristor controlled shunt compensation, establishing conditions for voltage support and unbalanced load compensation. Load balancing type SVC control system model development and validation is documented