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

Effect of water on electrical properties of Refined, Bleached, and Deodorized Palm Oil (RBDPO) as electrical insulating material

This paper describes the properties of refined, bleached, deodorized palm oil (RBDPO) as having the potential to be used as insulating liquid. There are several important properties such as electrical breakdown, dielectric dissipation factor, specific gravity, flash point, viscosity and pour point of RBDPO that was measured and compared to commercial mineral oil which is largely in current use as insulating liquid in power transformers. Experimental results of the electrical properties revealed that the average breakdown voltage of the RBDPO sample, without the addition of water at room temperature, is 13.368 kV. The result also revealed that due to effect of water, the breakdown voltage is lower than that of commercial mineral oil (Hyrax). However, the flash point and the pour point of RBDPO is very high compared to mineral oil thus giving it advantageous possibility to be used safely as insulating liquid. The results showed that RBDPO is greatly influenced by water, causing the breakdown voltage to decrease and the dissipation factor to increase; this is attributable to the high amounts of dissolved water

SIMULATION AND MITIGATION OF POWER QUALITY DISTURBANCES ON A DISTRIBUTION SYSTEM USING DVR

Voltage sag is the most important power quality problem faced by many industrial customers. Equipment such as process controllers, programmable logic controllers, adjustable speed drives, robotics, etc used in modern industrial plants are actually becoming more sensitive to voltage sags. Voltage sags are normally described by the magnitude variation and duration, and also characterized by unbalance, non-sinusoidal wave shape and phase angle shift. One of the most common mitigation solution is installing uninterrupted power supply (UPS). To meet the demand for more efficient mitigation solution, the Dynamic Voltage Restorer (DVR) will be deployed. When a fault occurs, either at the high voltage source end or at the consumer end, the DVR injects active and reactive power for the restoration of the voltage sags in the network. This thesis presents the power quality problems faced by the power distribution systems in general and then concentrates on analyzing an important and specific distribution system in particular. A dynamic voltage restorer (DVR) is connected on the 11KV of an utility feeder to Ipoh hospital, in reducing the voltage sags, that affect the operation of sensitive loads to the hospital. Case studies were conducted at four industrial sites (Hitachi plant and Nihoncanpack at Bemban, Filrex at Bercham and Ipoh Hospital) by monitoring and taking physical sag measurements for a period of one month. The real time measurements were carried out to identify the types power quality disturbances that exits in the various plants before providing the custom power device as a mitigation tool. The Ipoh Hospital is taken for a special case study since the hospital has to maintain high quality power supply to the medical equipments such as CT Scan, Magnetic Resonance Imaging (MRI), Magnetic Scanner, X-ray unit, and other life savingequipment. For simulation study, PSS/ADEPT and PSCAD/EMTDC software packages were used in modeling of the power distribution system. With the PSS/ADEPT simulation tool, the voltage severity is studied by introducing different types of faults. The PSCAD/EMTDC is a graphical user interface simulation tool to simulate sag waveforms for various types of faults. A DVR was modeled using the PSCAD/EMTDC software and simulated for voltage sag mitigation. The recorded waveform shows the DVR as a potential custom power solution provider. The DVR can improve the overall voltage regulation. The results obtained from the DVR show that the voltage sags are reduced by bringing the supply voltage level to 100%. The simulated results were verified for selected faults theoretically. v

Modeling and Analysis of Power Transformers under Ferroresonance Phenomenon

La Ferroresonancia és un dels fenòmens transitoris més destructius dels sistemes de potència. Associa inductàncies no lineals i capacitancias del sistema, iniciant-se de maneres diferents, el que fa molt difícil la seva caracterització. Per evitar les conseqüències de la ferrorresonancia cal entendre el fenomen, predir-i identificar-lo, per poder evitar-ho o eliminar-lo. No obstant això, el seu comportament complex no permet analitzar usant mètodes lineals. A causa de les no linealitats, la solució d'un circuit ferrorresonante s'obté generalment usant mètodes en el domini del temps; típicament, mètodes d'integració numèrica per ordinador, com ara el EMTP. Algunes eines per a l'enteniment, classificació i predicció de la ferrorresonancia es presenten en aquest estudi: mapes de Poincaré s'utilitzen per identificar el fenomen; Diagrames de Bifurcació s'utilitzen per detallar la ubicació dels canvis abruptes en estudis paramètric; Mapes 3D i 4D s'implementen per generalitzar el comportament complex del sistema. D'altra banda, els transformadors són sens dubte l'equip que requereix un modelatge més detallat. Els paràmetres utilitzats en el model han de ser adequats específicament per al tipus d'estudi a realitzar, d'una altra manera, les simulacions podrien no reproduir els casos correctament. En aquesta tesi, es presenten els detalls per modelar transformadors monofàsics i trifàsics. A més, es presenten noves tendències per representar fenòmens físics com el cicle d'histèresi.La Ferrorresonancia es uno de los fenómenos transitorios más destructivos de los sistemas de potencia. Asocia inductancias no lineales y capacitancias del sistema, iniciándose de maneras diferentes, lo que hace muy difícil su caracterización. Para evitar las consecuencias de la ferrorresonancia es necesario entender el fenómeno, predecirlo e identificarlo, para poder evitarlo o eliminarlo. Sin embargo, su comportamiento complejo no permite analizarlo usando métodos lineales. Debido a las no linealidades, la solución de un circuito ferrorresonante se obtiene generalmente usando métodos en el dominio del tiempo; típicamente, métodos de integración numérica por ordenador, tales como el EMTP. Algunas herramientas para el entendimiento, clasificación y predicción de la ferrorresonancia se presentan en este estudio: mapas de Poincaré se utilizan para identificar el fenómeno; Diagramas de Bifurcación se utilizan para detallar la ubicación de los cambios abruptos en estudios paramétrico; Mapas 3D y 4D se implementan para generalizar el comportamiento complejo del sistema. Por otro lado, los transformadores son sin duda el equipo que requiere un modelado más detallado. Los parámetros utilizados en el modelo deben ser adecuados específicamente para el tipo de estudio a realizar, de otra manera, las simulaciones podrían no reproducir los casos correctamente. En esta tesis, se presentan los detalles para modelar transformadores monofásicos y trifásicos. Además, se presentan nuevas tendencias para representar fenómenos físicos como el ciclo de histéresis.Ferroresonance is one of the most destructive transient phenomena in power systems. It involves the association of nonlinear magnetizing inductances and capacitances, and may be initiated in many different ways, making very difficult its characterization. To prevent the consequences of ferroresonance it is necessary to understand the phenomenon, predict and identify it, to finally avoid it or eliminate it. However, it cannot be analyzed or predicted by computation methods based on linear approximation. Because of nonlinearities, the solution of a ferroresonant circuit is usually obtained using time-domain methods; typically, a computer-based numerical integration method such as the EMTP. Tools for discerning, classifying and predicting ferroresonance are collected in this study: Poincaré maps are used to describe the time behavior of a system; Bifurcation Diagrams are utilized to detail the locations of all the abrupt changes in parametric study; 3D and 4D Maps can be implemented to generalize a complex system behavior. On the other hand, transformers are unquestionably the equipment demanding most detailed modeling. The parameters used in the model should be adequate specifically for the type of study to be performed, other way, the simulation may not reproduce the real cases. In this thesis, details are presented to modeling single- and three-phase transformers. In addition, new trends are presented to address important physical phenomenon such as hysteresis cycle

SIMULATION AND MITIGATION OF POWER QUALITY DISTURBANCES ON A DISTRIBUTION SYSTEM USING DVR

Voltage sag is the most important power quality problem faced by many industrial customers. Equipment such as process controllers, programmable logic controllers, adjustable speed drives, robotics, etc used in modern industrial plants are actually becoming more sensitive to voltage sags. Voltage sags are normally described by the magnitude variation and duration, and also characterized by unbalance, non-sinusoidal wave shape and phase angle shift. One of the most common mitigation solution is installing uninterrupted power supply (UPS). To meet the demand for more efficient mitigation solution, the Dynamic Voltage Restorer (DVR) will be deployed. When a fault occurs, either at the high voltage source end or at the consumer end, the DVR injects active and reactive power for the restoration of the voltage sags in the network. This thesis presents the power quality problems faced by the power distribution systems in general and then concentrates on analyzing an important and specific distribution system in particular. A dynamic voltage restorer (DVR) is connected on the 11KV of an utility feeder to Ipoh hospital, in reducing the voltage sags, that affect the operation of sensitive loads to the hospital. Case studies were conducted at four industrial sites (Hitachi plant and Nihoncanpack at Bemban, Filrex at Bercham and Ipoh Hospital) by monitoring and taking physical sag measurements for a period of one month. The real time measurements were carried out to identify the types power quality disturbances that exits in the various plants before providing the custom power device as a mitigation tool. The Ipoh Hospital is taken for a special case study since the hospital has to maintain high quality power supply to the medical equipments such as CT Scan, Magnetic Resonance Imaging (MRI), Magnetic Scanner, X-ray unit, and other life savingequipment. For simulation study, PSS/ADEPT and PSCAD/EMTDC software packages were used in modeling of the power distribution system. With the PSS/ADEPT simulation tool, the voltage severity is studied by introducing different types of faults. The PSCAD/EMTDC is a graphical user interface simulation tool to simulate sag waveforms for various types of faults. A DVR was modeled using the PSCAD/EMTDC software and simulated for voltage sag mitigation. The recorded waveform shows the DVR as a potential custom power solution provider. The DVR can improve the overall voltage regulation. The results obtained from the DVR show that the voltage sags are reduced by bringing the supply voltage level to 100%. The simulated results were verified for selected faults theoretically. v

Efficacy of Smart PV Inverter as a Strategic Mitigator of Network Harmonic Resonance and a Suppressor of Temporary Overvoltage Phenomenon in Distribution Systems

The research work explores the design of Smart PV inverters in terms of modelling and investigates the efficacy of a Smart PV inverter as a strategic mitigator of network harmonic resonance phenomenon and a suppressor of Temporary Overvoltage (TOV) in distribution systems. The new application and the control strategy of Smart PV inverters can also be extended to SmartPark-Plug in Electric Vehicles as the grid becomes smarter. As the grid is becoming smarter, more challenges are encountered with the integration of PV plants in distribution systems. Smart PV inverters nowadays are equipped with specialized controllers for exchanging reactive power with the grid based on the available capacity of the inverter, after the real power generation. Although present investigators are researching on several applications of Smart PV inverters, none of the research-work in real time and in documentation have addressed the benefits of employing Smart PV inverters to mitigate network resonances. U.S based standard IEEE 519 for power quality describes the network resonance as a major contributor that has an impact on the harmonic levels. This dissertation proposes a new application for the first time in utilizing a Smart PV inverter to act as a virtual detuner in mitigating network resonance. As a part of the Smart PV inverter design, the LCL filter plays a vital role on network harmonic resonance and further has a direct impact on the stability of the controller and rest of the distribution system. Temporary Overvoltage (TOV) phenomenon is more pronounced especially during unbalanced faults like single line to ground faults (SLGF) in the presence of PV. Such an abnormal incident can damage the customer loads. IEEE 142-“Effective grounding” technique is employed to design the grounding scheme for synchronous based generators. The utilities have been trying to make a PV system comply with IEEE 142 standard as well. Several utilities are still employing the same grounding schemes even now. The attempt has resulted in diminishing the efficacy of protection schemes. Further, millions of dollars and power has been wasted by the utilities. As a result, the concept of effective grounding for PV system has become a challenge when utilities try to mitigate TOV. With an intention of economical aspects in distribution systems planning, this dissertation also proposes a new application and a novel control scheme for utilizing Smart PV/Smart Park inverters to mitigate TOV in distribution systems for the first time. In other words, this novel application can serve as an effective and supporting schema towards ineffective grounding systems. PSCAD/EMTDC has been used throughout the course of research. The idea of Smart inverters serving as a virtual detuner in mitigating network harmonic resonance and as a TOV suppressor in distribution systems has been devised based on the basic principle of VAR injection and absorption with a new control strategy respectively. This research would further serve as a pioneering approach for researchers and planning engineers working in distribution systems

Applications and measurement techniques for a reliable and affordable innovative power quality analysis system

Viene preso in considerazione e analizzato il problema della valutazione e dellamisura della qualità dell’energia elettrica al fine di poter ottenere uno strumento che sia in grado di fornire informazioni affidabili e precise, ma senza comportare necessariamente un costo eccessivamente oneroso perchè ottenute con sistemi anche non tradizionali, e utili alla disamina dei problemi riscontrabili nel sistema elettrico favorendone l'individuazione delle cause e quindi la loro risoluzion

Multilevel Monte Carlo approach for estimating reliability of electric distribution systems

Most of the power outages experienced by the customers are due to the failures in the electric distribution systems. However, the ultimate goal of a distribution system is to meet customer electricity demand by maintaining a satisfactory level of reliability with less interruption frequency and duration as well as less outage costs. Quantitative evaluation of reliability is, therefore, a significant aspect of the decision-making process in planning and designing for future expansion of network or reinforcement. Simulation approach of reliability evaluation is generally based on sequential Monte Carlo (MC) method which can consider the random nature of system components. Use of MC method for obtaining accurate estimates of the reliability can be computationally costly particularly when dealing with rare events (i.e. when high accuracy is required). This thesis proposes a simple and effective methodology for accelerating MC simulation in distribution systems reliability evaluation. The proposed method is based on a novel Multilevel Monte Carlo (MLMC) simulation approach. MLMC approach is a variance reduction technique for MC simulation which can reduce the computational burden of the MC method dramatically while both sampling and discretisation errors are considered for converging to a controllable accuracy level. The idea of MLMC is to consider a hierarchy of computational meshes (levels) instead of using single time discretisation level in MC method. Most of the computational effort in MLMC method is transferred from the finest level to the coarsest one, leading to substantial computational saving. As the simulations are conducted using multiple approximations, therefore the less accurate estimate on the preceding coarse level can be sequentially corrected by averages of the differences of the estimations of two consecutive levels in the hierarchy. In this dissertation, we will find the answers to the following questions: can MLMC method be used for reliability evaluation? If so, how MLMC estimators for reliability evaluation are constructed? Finally, how much computational savings can we expect through MLMC method over MC method? MLMC approach is implemented through solving the stochastic differential equations of random variables related to the reliability indices. The differential equations are solved using different discretisation schemes. In this work, the performance of two different discretisation schemes, Euler-Maruyama and Milstein are investigated for this purpose. We use the benchmark Roy Billinton Test System as the test system. Based on the proposed MLMC method, a number of reliability studies of distribution systems have been carried out in this thesis including customer interruption frequency and duration based reliability assessment, cost/benefits estimation, reliability evaluation incorporating different time-varying factors such as weather-dependent failure rate and restoration time of components, time-varying load and cost models of supply points. The numerical results that demonstrate the computational performances of the proposed method are presented. The performances of the MLMC and MC methods are compared. The results prove that MLMC method is computationally efficient compared to those derived from standard MC method and it can retain an acceptable level of accuracy. The novel computational tool including examples presented in this thesis will help system planners and utility managers to provide useful information of reliability of distribution networks. With the help of such tool they can take necessary steps to speed up the decision-making process of reliability improvement.Thesis (Ph.D.) -- University of Adelaide, School of Electrical and Electronic Engineering, 201