Matching Items (253)
Description
Electric power systems are facing great challenges from environmental regulations, changes in demand due to new technologies like electric vehicle, as well as the integration of various renewable energy sources. These factors taken together require the development of new tools to help make policy and investment decisions for the future power grid. The requirements of a network equivalent to be used in such planning tools are very different from those assumed in the development of traditional equivalencing procedures. This dissertation is focused on the development, implementation and verification of two network equivalencing approaches on large power systems, such as the Eastern Interconnection. Traditional Ward-type equivalences are a class of equivalencing approaches but this class has some significant drawbacks. It is well known that Ward-type equivalents "smear" the injections of external generators over a large number of boundary buses. For newer long-term investment applications that take into account such things as greenhouse gas (GHG) regulations and generator availability, it is computationally impractical to model fractions of generators located at many buses. A modified-Ward equivalent is proposed to address this limitation such that the external generators are moved wholesale to some internal buses based on electrical distance. This proposed equivalencing procedure is designed so that the retained-line power flows in the equivalent match those in the unreduced (full) model exactly. During the reduction process, accommodations for special system elements are addressed, including static VAr compensators (SVCs), high voltage dc (HVDC) transmission lines, and phase angle regulators. Another network equivalencing approach based on the dc power flow assumptions and the power transfer distribution factors (PTDFs) is proposed. This method, rather than eliminate buses via Gauss-reduction, aggregates buses on a zonal basis. The bus aggregation approach proposed here is superior to the existing bus aggregation methods in that a) under the base case, the equivalent-system inter-zonal power flows exactly match those calculated using the full-network-model b) as the operating conditions change, errors in line flows are reduced using the proposed bus clustering algorithm c) this method is computationally more efficient than other bus aggregation methods proposed heretofore. A critical step in achieving accuracy with a bus aggregation approach is selecting which buses to cluster together and how many clusters are needed. Clustering in this context refers to the process of partitioning a network into subsets of buses. An efficient network clustering method is proposed based on the PTDFs and the data mining techniques. This method is applied to the EI topology using the "Saguaro" supercomputer at ASU, a resource with sufficient memory and computational capability for handling this 60,000-bus and 80,000-branch system. The network equivalents generated by the proposed approaches are verified and tested for different operating conditions and promising results have been observed.
ContributorsShi, Di (Author) / Tylavsky, Daniel J (Thesis advisor) / Vittal, Vijay (Committee member) / Hedman, Kory (Committee member) / Ayyanar, Raja (Committee member) / Arizona State University (Publisher)
Created2012
Description
In electric power systems, phasor measurement units (PMUs) are capable of providing synchronized voltage and current phasor measurements which are superior to conventional measurements collected by the supervisory control and data acquisition (SCADA) system in terms of resolution and accuracy. These measurements are known as synchrophasor measurements. Considerable research work has been done on the applications of PMU measurements based on the as-sumption that a high level of accuracy is obtained in the field. The study in this dissertation is conducted to address the basic issue concerning the accuracy of actual PMU measurements in the field. Synchronization is one of the important features of PMU measurements. However, the study presented in this dissertation reveals that the problem of faulty synchronization between measurements with the same time stamps from different PMUs exists. A Kalman filter model is proposed to analyze and calcu-late the time skew error caused by faulty synchronization. In order to achieve a high level of accuracy of PMU measurements, inno-vative methods are proposed to detect and identify system state changes or bad data which are reflected by changes in the measurements. This procedure is ap-plied as a key step in adaptive Kalman filtering of PMU measurements to over-come the insensitivity of a conventional Kalman filter. Calibration of PMU measurements is implemented in specific PMU instal-lation scenarios using transmission line (TL) parameters from operation planning data. The voltage and current correction factors calculated from the calibration procedure indicate the possible errors in PMU measurements. Correction factors can be applied in on-line calibration of PMU measurements. A study is conducted to address an important issue when integrating PMU measurements into state estimation. The reporting rate of PMU measurements is much higher than that of the measurements collected by the SCADA. The ques-tion of how to buffer PMU measurements is raised. The impact of PMU meas-urement buffer length on state estimation is discussed. A method based on hy-pothesis testing is proposed to determine the optimal buffer length of PMU meas-urements considering the two conflicting features of PMU measurements, i. e. un-certainty and variability. Results are presented for actual PMU synchrophasor measurements.
ContributorsZhang, Qing (Author) / Heydt, Gerald (Thesis advisor) / Vittal, Vijay (Thesis advisor) / Ayyanar, Raja (Committee member) / Si, Jennie (Committee member) / Arizona State University (Publisher)
Created2012
Description
This thesis presents a new technique to develop an air-conditioner (A/C) compressor single phase induction motor model for use in an electro-magnetic transient program (EMTP) simulation tool. The method developed also has the capability to represent multiple units of the component in a specific three-phase distribution feeder and investigate the phenomenon of fault-induced delayed voltage recovery (FIDVR) and the cause of motor stalling. The system of differential equations representing the single phase induction motor model is developed and formulated. Implicit backward Euler method is applied to numerically integrate the stator currents that are to be drawn from the electric network. The angular position dependency of the rotor shaft is retained in the inductance matrix associated with the model to accurately capture the dynamics of the motor loads. The equivalent circuit of the new model is interfaced with the electric network in the EMTP. The dynamic response of the motor when subjected to faults at different points on voltage waveform has been studied using the EMTP simulator. The mechanism and the impacts of motor stalling need to be explored with multiple units of the detailed model connected to a realistic three-phase distribution system. The model developed can be utilized to assess and improve the product design of compressor motors by air-conditioner manufacturers. Another critical application of the model would be to examine the impacts of asymmetric transmission faults on distribution systems to investigate and develop mitigation measures for the FIDVR problem.
ContributorsLiu, Yuan (Author) / Vittal, Vijay (Thesis advisor) / Undrill, John (Committee member) / Ayyanar, Raja (Committee member) / Arizona State University (Publisher)
Created2012
Description
This research work illustrates the use of software packages based on the concept of nu-merical analysis technique to evaluate the electric field and voltage distribution along composite insulators for system voltages ranging from 138 kV up to 1200 kV ac. A part of the calculations was made using the 3D software package, COULOMB 8.0, based on the concept of Boundary Element Method (BEM). The electric field was calculated under dry and wet conditions. Compo-site insulators experience more electrical stress when compared to porcelain and are also more prone to damage caused by corona activity. The work presented here investigates the effect of corona rings of specific dimensions and bundled conductors on the electric field along composite insulators. Inappropriate placement or dimensions of corona rings could enhance the electric field instead of mitigating it. Corona ring optimization for a 1000 kV composite insulator was per-formed by changing parameters of the ring, such as the diameter of the ring, thickness of the ring tube and the projection of the ring from the high voltage energized end fitting. Grading rings were designed for Ultra High Voltage (UHV) systems that use two units of composite insulators in pa-rallel. The insulation distance, which bears 50% of the total applied voltage, is raised by 61% with the grading ring installed, when compared to the distance without the grading ring. In other words, the electric field and voltage distribution was found to be more linear with the application of grad-ing rings. The second part of this project was carried out using the EPRI designed software EPIC. This is based on the concept of Charge Simulation method (CSM). Comparisons were made be-tween electric field magnitude along composite insulators used for suspension and dead end configuration for system voltages ranging from 138 kV to 500 kV. It was found that the dead end composite insulators experience significantly higher electrical stress when compared to their suspension counterpart. It was also concluded that this difference gets more prominent as the system voltage increases. A comparison made between electric field distribution along composite insulators used in single and double dead end structures suggested that the electric stress experienced by the single dead end composite insulators is relatively higher when compared to double dead end composite insulators.
ContributorsDoshi, Tanushri (Author) / Gorur, Ravi S (Thesis advisor) / Vittal, Vijay (Committee member) / Farmer, Richard (Committee member) / Arizona State University (Publisher)
Created2010
Description
Composite insulators on overhead lines are frequently subjected to corona discharges due to increased electric field intensities under various conditions. These discharges can cause localized heating on the surface and affect the hydrophobicity of the insulator. A study has been undertaken to quantify and evaluate the thermal degradation that composite insulation is subjected to from corona discharges. This has been conducted primarily at the power frequency (60 Hz) and at the low frequency range (37 kHz). Point to plane corona discharge experiments have been performed in the laboratory at both the frequencies and varying levels of thermal degradation has been observed. The amplitude and the frequency of current spikes have been recorded at different voltage levels. A temperature model based on the amplitude and the frequency of current data has been formulated to calculate the maximum temperature attained due to these discharges. Visual thermal degradation has been found to set in at a low frequency range while there is no visual degradation observed at power frequency even when exposed to discharges for relatively much longer periods of time. However, microscopic experiments have been conducted which revealed degradation on the surface at 60 Hz. It has also been found that temperatures in excess of 300 Celsius have been obtained at 37 kHz. This corroborates the thermo gravimetric analysis data that proves thermal degradation in silicone rubber samples at temperatures greater than 300 Celsius. Using the above model, the maximum temperature rise can be evaluated due to discharges occurring on high voltage insulation. This model has also been used to calculate the temperature rise on medium voltage distribution equipment such as composite bushings and stand-off plugs. The samples were subjected to standard partial discharge tests and the corresponding discharge magnitudes have been recorded. The samples passed the tests and the corresponding temperatures plotted have been found to be within thermal limits of the respective insulation used on the samples. The experimental results concur with the theoretical model. A knowledge of the maximum temperatures attained due to these discharges can help in design of insulation with better thermal properties.
ContributorsSangaraju Venkateshwara, Pradeep Varma (Author) / Gorur, Ravi S (Thesis advisor) / Farmer, Richard (Committee member) / Vittal, Vijay (Committee member) / Arizona State University (Publisher)
Created2010
Description
After a power system blackout, system restoration is the most important task for the operators. Most power systems rely on an off&ndashline; restoration plan and the experience of operators to select scenarios for the black start path. Using an off&ndashline; designed restoration plan based on past experience may not be the most reliable approach under changing network configurations and loading levels. Hence, an objective restoration path selection procedure, including the option to check constraints, may be more responsive in providing directed guidance to the operators to identify the optimal transmission path to deliver power to other power plants or to pick up load as needed. After the system is subjected to a blackout, parallel restoration is an efficient way to speed up the restoration process. For a large scale power system, this system sectionalizing problem is quite complicated when considering black&ndashstart; constraints, generation/load balance constraints and voltage constraints. This dissertation presents an ordered binary decision diagram (OBDD) &ndashbased; system sectionalizing method, by which the splitting points can be quickly found. The simulation results on the IEEE 39 and 118&ndashbus; system show that the method can successfully split the system into subsystems satisfying black&ndashstart; constraints, generation/load balance constraints and voltage constraints. A power transfer distribution factor (PTDF)&ndashbased; approach will be described in this dissertation to check constraints while restoring the system. Two types of restoration performance indices are utilized considering all possible restoration paths, which are then ranked according to their expected performance characteristics as reflected by the restoration performance index. PTDFs and weighting factors are used to determine the ordered list of restoration paths, which can enable the load to be picked up by lightly loaded lines or relieve stress on heavily loaded lines. A transmission path agent can then be formulated by performing the automatic path selection under different system operating conditions. The proposed restoration strategy is tested on the IEEE&ndash39; bus system and on the Western region of the Entergy system. The testing results reveal that the proposed strategy can be used in real time.
ContributorsWang, Chong (Author) / Vittal, Vijay (Thesis advisor) / Tylavsky, Daniel (Committee member) / Heydt, Gerald (Committee member) / Farmer, Richard (Committee member) / Arizona State University (Publisher)
Created2010
Description
An advantage of doubly fed induction generators (DFIGs) as compared to conventional fixed speed wind turbine generators is higher efficiency. This higher efficiency is achieved due to the ability of the DFIG to operate near its optimal turbine efficiency over a wider range of wind speeds through variable speed operation. This is achieved through the application of a back-to-back converter that tightly controls the rotor current and allows for asynchronous operation. In doing so, however, the power electronic converter effectively decouples the inertia of the turbine from the system. Hence, with the increase in penetration of DFIG based wind farms, the effective inertia of the system will be reduced. With this assertion, the present study is aimed at identifying the systematic approach to pinpoint the impact of increased penetration of DFIGs on a large realistic system. The techniques proposed in this work are tested on a large test system representing the Midwestern portion of the U.S. Interconnection. The electromechanical modes that are both detrimentally and beneficially affected by the change in inertia are identified. The combination of small-signal stability analysis coupled with the large disturbance analysis of exciting the mode identified is found to provide a detailed picture of the impact on the system. The work is extended to develop suitable control strategies to mitigate the impact of significant DFIG penetration on a large power system. Supplementary control is developed for the DFIG power converters such that the effective inertia contributed by these wind generators to the system is increased. Results obtained on the large realistic power system indicate that the frequency nadir following a large power impact is effectively improved with the proposed control strategy. The proposed control is also validated against sudden wind speed changes in the form of wind gusts and wind ramps. The beneficial impact in terms of damping power system oscillations is observed, which is validated by eigenvalue analysis. Another control mechanism is developed aiming at designing the power system stabilizer (PSS) for a DFIG similar to the PSS of synchronous machines. Although both the supplementary control strategies serve the purpose of improving the damping of the mode with detrimental impact, better damping performance is observed when the DFIG is equipped with both the controllers.
ContributorsGautam, Durga (Author) / Vittal, Vijay (Thesis advisor) / Heydt, Gerald (Committee member) / Ayyanar, Raja (Committee member) / Farmer, Richard (Committee member) / Si, Jennie (Committee member) / Arizona State University (Publisher)
Created2010
Description
Market acceptability of distributed energy resource (DER) technologies and the gradual and consistent increase in their depth of penetration have generated significant interest over the past few years. In particular, in Arizona and several other states there has been a substantial in-crease in distributed photovoltaic (PV) generation interfaced to the power distribution systems, and is expected to continue to grow at a significant rate. This has made integration, control and optimal operation of DER units a main area of focus in the design and operation of distribution systems. Grid-connected, distributed PV covers a wide range of power levels ranging from small, single phase residential roof-top systems to large three-phase, multi-megawatt systems. The focus of this work is on analyzing large, three-phase systems, with the power distribution system of the Arizona State University (ASU) Tempe campus used as the test bed for analysis and simulation. The Tempe campus of ASU has presently 4.5 MW of installed PV capacity, with another 4.5 MW expected to be added by 2011, which will represent about 22% of PV penetration. The PV systems are interfaced to the grid invariably by a power electronic inverter. Many of the important characteristics of the PV generation are influenced by the design and performance of the inverter, and hence suitable models of the inverter are needed to analyze PV systems. Several models of distributed generation (DG), including switching and average models, suitable for different study objectives, and different control modes of the inverter have been described in this thesis. A critical function of the inverters is to quickly detect and eliminate unintentional islands during grid failure. In this thesis, many active anti-islanding techniques with voltage and frequency positive feedback have been studied. Effectiveness of these techniques in terms of the tripping times specified in IEEE Std. 1547 for interconnecting distributed resources with electric power systems has been analyzed. The impact of distributed PV on the voltage profile of a distribution system has been ana-lyzed with ASU system as the test bed using power systems analysis tools namely PowerWorld and CYMDIST. The present inverters complying with IEEE 1547 do not regulate the system vol-tage. However, the future inverters especially at higher power levels are expected to perform sev-eral grid support functions including voltage regulation and reactive power support. Hence, the impact of inverters with the reactive power support capabilities is also analyzed. Various test sce-narios corresponding to different grid conditions are simulated and it is shown that distributed PV improves the voltage profile of the system. The improvements are more significant when the PV generators are capable of reactive power support. Detailed short circuit analyses are also per-formed on the system, and the impact of distributed PV on the fault current magnitude, with and without reactive power injection, have been studied.
ContributorsNarayanan, Anand (Author) / Ayyanar, Raja (Thesis advisor) / Vittal, Vijay (Committee member) / Heydt, Gerald T (Committee member) / Arizona State University (Publisher)
Created2010
Description
The impact of increasing penetration of converter control-based generators (CCBGs) in a large-scale power system is assessed through a model based small signal stability analysis. Three test bed cases for the years 2010, 2020, and 2022 of the Western Electricity Coordinating Council (WECC) in the United States are used for the analysis. Increasing penetration of wind-based Type 3 and wind-based Type 4 and PV Solar CCBGs is used in the tests. The participation and interaction of CCBGs and synchronous generators in traditional electromechanical interarea modes is analyzed. Two new types of modes dominated by CCBGs are identified. The characteristics of these new modes are described and compared to electromechanical modes in the frequency domain. An examination of the mechanism of the interaction between the CCBG control states and the synchronous generator control states is presented and validated through dynamic simulations. Actual system and forecast load data are used throughout.
ContributorsQuintero, Jaime (Author) / Vittal, Vijay (Author) / Heydt, Gerald (Author) / Zhang, Hui (Author) / Ira A. Fulton Schools of Engineering (Contributor) / School of Electrical, Computer and Energy Engineering (Contributor)
Created2014-09-01
Description
The Java-Bali power system is the biggest power system in Indonesia. On September 5th, 2018 at 11:26 AM, a region in the East Java-Bali subsystem suffered a blackout due to a single line to ground fault that disrupted the stability of the interconnected system and caused cascaded tripping.
This thesis presents the results of an evaluation of the dynamic performance of the East Java-Bali subsystem. It involves the static and dynamic simulations of the sequence of events that led to the East Java Bali subsystem blackout, especially the impact of the loss of a set of 500 kV transmission lines, which in reality was suspected to be the main cause.
The basic calculations related to power system state and familiarization with PSS/E (a commercial power system analysis software package) are first demonstrated. A simple 3-bus system test is taken as an example. The steady state characteristics of the active and reactive power injection, voltage and phase angle are calculated manually and compared to the PSS/E simulation results. As for the dynamic characteristics, short circuit current, electrical and mechanical power, rotor angle, and fault clearing time are determined by observing the plots of the simulation results. Based on understanding of the PSS/E modeling and simulation, the configuration, generation, and loading of the simplified East Java-Bali subsystem is evaluated. The generators (including the excitation system and governor) and transmission lines parameters are updated, as the reference model for the study. The model is validated by the actual data (active power flow) before the fault. Single line to ground fault and loss of generation disturbances were simulated to observe the stability of the system.
The analysis of the blackout is conducted through the simulation results based on all relevant documentation (such as fault report and sequence of events). With respect to the sequence of events (a single line to ground fault on the 500kV transmission lines, overload on 150kV transmission lines and tripping of power plants), several simulations of the East Java-Bali subsystem operations provided in the official blackout report are evaluated. Finally, the undervoltage load shedding strategy is evaluated and proposed as a solution to mitigate the blackout in the East Java-Bali subsystem.
The simulations reveal some interesting results regarding the operational characteristics of the East Java-Bali subsystem before the disturbances and during the cascaded tripping.
This thesis presents the results of an evaluation of the dynamic performance of the East Java-Bali subsystem. It involves the static and dynamic simulations of the sequence of events that led to the East Java Bali subsystem blackout, especially the impact of the loss of a set of 500 kV transmission lines, which in reality was suspected to be the main cause.
The basic calculations related to power system state and familiarization with PSS/E (a commercial power system analysis software package) are first demonstrated. A simple 3-bus system test is taken as an example. The steady state characteristics of the active and reactive power injection, voltage and phase angle are calculated manually and compared to the PSS/E simulation results. As for the dynamic characteristics, short circuit current, electrical and mechanical power, rotor angle, and fault clearing time are determined by observing the plots of the simulation results. Based on understanding of the PSS/E modeling and simulation, the configuration, generation, and loading of the simplified East Java-Bali subsystem is evaluated. The generators (including the excitation system and governor) and transmission lines parameters are updated, as the reference model for the study. The model is validated by the actual data (active power flow) before the fault. Single line to ground fault and loss of generation disturbances were simulated to observe the stability of the system.
The analysis of the blackout is conducted through the simulation results based on all relevant documentation (such as fault report and sequence of events). With respect to the sequence of events (a single line to ground fault on the 500kV transmission lines, overload on 150kV transmission lines and tripping of power plants), several simulations of the East Java-Bali subsystem operations provided in the official blackout report are evaluated. Finally, the undervoltage load shedding strategy is evaluated and proposed as a solution to mitigate the blackout in the East Java-Bali subsystem.
The simulations reveal some interesting results regarding the operational characteristics of the East Java-Bali subsystem before the disturbances and during the cascaded tripping.
ContributorsRoekman, Taufan Marviansha (Author) / Vittal, Vijay (Thesis director) / Pal, Anamitra (Committee member) / Electrical Engineering Program (Contributor, Contributor) / Barrett, The Honors College (Contributor)
Created2019-12