PMU-Based ROCOF Measurements: Uncertainty Limits and Metrological Significance in Power System Applications

In modern power systems, the Rate-of-Change-of-Frequency (ROCOF) may be largely employed in Wide Area Monitoring, Protection and Control (WAMPAC) applications. However, a standard approach towards ROCOF measurements is still missing. In this paper, we investigate the feasibility of Phasor Measurement Units (PMUs) deployment in ROCOF-based applications, with a specific focus on Under-Frequency Load-Shedding (UFLS). For this analysis, we select three state-of-the-art window-based synchrophasor estimation algorithms and compare different signal models, ROCOF estimation techniques and window lengths in datasets inspired by real-world acquisitions. In this sense, we are able to carry out a sensitivity analysis of the behavior of a PMU-based UFLS control scheme. Based on the proposed results, PMUs prove to be accurate ROCOF meters, as long as the harmonic and inter-harmonic distortion within the measurement pass-bandwidth is scarce. In the presence of transient events, the synchrophasor model looses its appropriateness as the signal energy spreads over the entire spectrum and cannot be approximated as a sequence of narrow-band components. Finally, we validate the actual feasibility of PMU-based UFLS in a real-time simulated scenario where we compare two different ROCOF estimation techniques with a frequency-based control scheme and we show their impact on the successful grid restoration.Comment: Manuscript IM-18-20133R. Accepted for publication on IEEE Transactions on Instrumentation and Measurement (acceptance date: 9 March 2019

Analytical techniques and instrumentation, a compilation

Procedures for conducting materials tests and structural analyses of aerospace components are presented as a part of the NASA technology utilization program. Some of the subjects discussed are as follows: (1) failures in cryogenic tank insulation, (2) friction characteristics of graphite and graphite-metal combinations, (3) evaluation of polymeric products in thermal-vacuum environment, (4) erosion of metals by multiple impacts with water, (5) mass loading effects on vibrated ring and shell structures, (6) nonlinear damping in structures, and (7) method for estimating reliability of randomly excited structures

Load shedding in network monitoring applications

Monitoring and mining real-time network data streams are crucial operations for managing and operating data networks. The information that network operators desire to extract from the network traffic is of different size, granularity and accuracy depending on the measurement task (e.g., relevant data for capacity planning and intrusion detection are very different). To satisfy these different demands, a new class of monitoring systems is emerging to handle multiple and arbitrary monitoring applications. Such systems must inevitably cope with the effects of continuous overload situations due to the large volumes, high data rates and bursty nature of the network traffic. These overload situations can severely compromise the accuracy and effectiveness of monitoring systems, when their results are most valuable to network operators. In this thesis, we propose a technique called load shedding as an effective and low-cost alternative to over-provisioning in network monitoring systems. It allows these systems to handle efficiently overload situations in the presence of multiple, arbitrary and competing monitoring applications. We present the design and evaluation of a predictive load shedding scheme that can shed excess load in front of extreme traffic conditions and maintain the accuracy of the monitoring applications within bounds defined by end users, while assuring a fair allocation of computing resources to non-cooperative applications. The main novelty of our scheme is that it considers monitoring applications as black boxes, with arbitrary (and highly variable) input traffic and processing cost. Without any explicit knowledge of the application internals, the proposed scheme extracts a set of features from the traffic streams to build an on-line prediction model of the resource requirements of each monitoring application, which is used to anticipate overload situations and control the overall resource usage by sampling the input packet streams. This way, the monitoring system preserves a high degree of flexibility, increasing the range of applications and network scenarios where it can be used. Since not all monitoring applications are robust against sampling, we then extend our load shedding scheme to support custom load shedding methods defined by end users, in order to provide a generic solution for arbitrary monitoring applications. Our scheme allows the monitoring system to safely delegate the task of shedding excess load to the applications and still guarantee fairness of service with non-cooperative users. We implemented our load shedding scheme in an existing network monitoring system and deployed it in a research ISP network. We present experimental evidence of the performance and robustness of our system with several concurrent monitoring applications during long-lived executions and using real-world traffic traces.Postprint (published version

Wide-area Situational Awareness Application Developments

This dissertation expands the topics from the wide-area situational awareness application development, system architecture design, to power system disturbance analysis. All the works are grounded on the wide-area Frequency Monitoring Network (FNET). The FNET system takes GPS-synchronized wide-area measurements in a low-cost, easily deployable manner at 120V single-phase power outlet. These synchronized observations enables the monitoring of bulk power systems, and provides critical information for understanding power system disturbances and system operations. Firstly, the work addresses the viability of angle measurement to serve different types of situational awareness applications, including the development of new angle-based event location estimation methods, the design of real-time system visualization framework using angle measurement. Secondly, a sound FNET power system event monitoring and automatic event reporting system framework is introduced, with NERC Frequency Response Initiative (FRI) tasks included to improve power system situational awareness capability. Lastly, the work covers different types of power system disturbance analysis, including the statistical analysis of frequency disturbances in NA power grid from 2008 to 2011; analysis of typical frequency response characteristics of the generation and load loss events in Europe power grid; analysis of some major disturbances in NA power grid from 2010 to 2011; and the inter-area oscillation modal analysis in the WECC system