An experimental Pressure Sensitive Paint (PSP) study of the unsteady pressure fields downstream of and on an oscillating hemispherical turret at subsonic freestream Mach numbers between 0.3 and 0.6 ...and Reynolds numbers of about 2 million is presented. The oscillating turret consisted of a hemispheric shell, mounted on an aluminum rectangular plate and is designed to oscillate in the spanwise direction at a single frequency, which lies within the frequency range of the dominant wake motion. The resonant-based aero-elastic response of the turret to the flow resulted in intermittent turret oscillations. Pressure fluctuations in the wake were found to be less energetic for the oscillating turret and the size of the recirculating region was increased, compared to the stationary turret. POD-based modal analysis of the pressure fields revealed that the wake dynamics is characterized by global anti-symmetric and symmetric shedding and showed that the oscillating turret primarily suppressed the global anti-symmetric shedding. The analysis of the unsteady forces acting on the turret demonstrated that the oscillating turret reduces the spanwise component of the unsteady force, while keeping other force components mostly unchanged. Intermittent nature of the spanwise force, which is responsible for the intermittent motion of the oscillating turret, was observed and discussed.
The paper considers the classification of steel cylindrical tanks failure from the action of seismic loads. Features of static calculation of tanks were revealed. Physical and mechanical properties ...of the material and geometric parameters of the vertical tank were determined. A full-size finite element model of a filled vertical steel tank has been developed. The calculation of the filled vertical steel tank was performed. The values of frequencies and periods of natural oscillations were obtained. Finite element method that was implemented in LIRA-multifunctional software package allows to design and calculate the structures for various purposes.
•Ability to trace the source of both forced and natural oscillations.•PMU application providing actionable information for operations.•Efficiency confirmed by multiple simulated and actual ...events.•Estimation of generator’s damping contribution into specific mode.
The modification of an energy-based approach called the dissipating energy flow (DEF) method is proposed, which uses data from phasor measurement units (PMUs) to trace the source of poorly damped natural and forced oscillations in power systems. The original energy-based approach (Chen et al., 2013) assumes the ability to determine steady-state values of variables measured by PMU during the transient process and that prevents the reliable use of the original method with actual PMU data. PMU data processing, proposed in the DEF method, is a key step in converting the energy-based method into a robust and automated tool for use with actual PMU data. The effectiveness of the proposed DEF method is demonstrated by testing multiple simulated cases of sustained oscillations, including both poorly damped natural and forced oscillations and more than 30 actual events in ISO New England (ISO-NE) and two events in Western Electricity Coordination Council (WECC) systems. The study also demonstrates the potential for using the DEF method to estimate the contribution of any generator to the damping of a specific oscillation mode.
This paper discusses a recent event in the western American power system when a forced oscillation was observed at a frequency that was close to a well-known 0.38-Hz inter-area electromechanical mode ...frequency of the western system. The event motivates a systematic investigation in this paper on the possibility of resonant interactions between forced oscillations and electromechanical inter-area oscillatory modes in power systems. When the natural oscillatory mode of a power system is poorly damped, and the forced oscillation occurs at a frequency close to system mode frequency at critical locations for the mode, resonance is observed in simulation test cases of the paper. It is shown that the MW oscillations on tie-lines can be as high as 477 MW from a 10-MW forced oscillation in Kundur test system because of resonance. This paper discusses the underlying system conditions and effects as related to resonance in power systems caused by forced oscillations and discusses ways to detect such scenarios using synchrophasors. Simulated data from Kundur two-area test power system as well as measurement data from western American power system are used to study the effect of forced oscillations in power systems.
Sustained oscillations persist without decay, impacting system stability and performance. Sustained oscillations in distribution systems exhibit unique mechanisms compared to those in transmission ...systems, yet research in this area of distribution systems is lacking. In distribution systems, these oscillations degrade power quality, jeopardizing stability and causing relay malfunctions and supply discontinuity. Understanding their mechanisms in modern distribution systems is crucial for their detection, classification, and localization. This paper provides a comprehensive review of sustained oscillations in modern distribution systems. Additionally, it discusses key methodologies for detecting and classifying sustained oscillations in transmission systems. Finally, it applies transmission system methodologies to real cases in Ontario's distribution system, shedding light on challenges and future directions.
This paper proposes a data-driven algorithm for locating the source of forced oscillations and suggests a physical interpretation for the method. By leveraging the sparsity of forced oscillations ...along with the low-rank nature of synchrophasor data, the problem of source localization under resonance conditions is cast as computing the sparse and low-rank components using Robust Principal Component Analysis (RPCA), which can be efficiently solved by the exact Augmented Lagrange Multiplier method. Based on this problem formulation, an efficient and practically implementable algorithm is proposed to pinpoint the forced oscillation source during real-time operation. Furthermore, theoretical insights are provided for the efficacy of the proposed approach, by use of physical model-based analysis, specifically by highlighting the low-rank nature of the resonance component matrix. Without the availability of system topology information, the proposed method can achieve high localization accuracy in synthetic cases based on benchmark systems and real-world forced oscillations in the power grid of Texas.
The article describes the experience of a successful online implementation of the Dissipating Energy Flow method for locating the source of oscillations in the Oscillation Source Locating (OSL) ...application. The OSL is a key component of the online oscillation management at ISO New England and in operation since September 2017. The article includes analysis of 1000+ actual oscillatory events processed by the OSL demonstrating the efficiency of the process in locating the source of oscillations.
Sudden occurrence of a large forced oscillation (FO) is a challenging problem for power system operators, especially when the forced oscillation is resonating with a natural system mode. Among the ...methods for oscillation source location, the energy flow method has shown promise for detecting the source of a natural oscillation as well as a forced oscillation. In this paper, we analyze the performance of the energy flow method in depth by evaluating the expressions of incremental energy in one period of the forced oscillation and by looking at a wide range of forced oscillation frequencies. We show that the energy flow based method can misidentify sources of forced oscillations. That is, the method may not be able to locate the true forced oscillation source as well as identify a non-source device to be the source. Examples are shown for systems with different damping levels of system modes and for different load composition types.
We present a new methodology to identify if forced oscillation (FO) sources are located in excitation systems or turbine governors. In this context, we propose to harness the information that dynamic ...state estimation (DSE) provides to be able to apply a dissipating energy flow (DEF) method. Measurements from phasor measurement units (PMUs) are used to estimate the internal states of different generators connected to the same bus. Using these estimations, we compute energy functions for the mechanical control loop and for the excitation control loop to determine where the FO was originated. Simulated signals from the IEEE-NASPI Oscillation Source Location (OSL) Contest are used to show that our proposal provides an online systematic methodology for identification and location of power systems forced oscillations, even when current measurements of the generator causing the FO are missing.
•To introduce a new procedure capable of identifying forced oscillations.•The control loop where the forced oscillation was originated can be identified.•Useful for scenarios with a limited number of phasor current measurements.•The forced oscillations can be detected and identified in tens of seconds.•To provide a robustness analysis for the entire identification procedure.
Accurately locating Forced Oscillations (FOs) source(s) in a large-scale power system is a challenging task, and an important aspect of power system operation. In this paper, a complementary use of ...Deep Learning (DL)-based and Dissipating Energy Flow (DEF)-based methods are proposed to localize forced oscillation source(s) using data from Phasor Measurement Units (PMUs), by tracing the forced oscillations source(s) on the branch level in the power system network. The robustness, effectiveness and speed of the proposed approach is demonstrated in a WECC 240-bus test system, with high renewable integration in the system. Several simulated cases were tested, including non-gaussian noise, partially observable system, and operational topology variations in the system which correspond to real-world challenges. Timely localization of forced oscillation at an early stage provides the opportunity for taking remedial reaction. The results show that without the information of system operational topology, the proposed method can achieve high localization accuracy in only 0.33 s.
•A Deep-Learning based approach for forced oscillations is proposed.•It has reliable and robust performance in the presence of topology variation.•It significantly restricts the required information.•It is able to reliably detect multiple oscillation sources simultaneously.
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