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Schoene J.,Enernex Corporation | Uman M.A.,University of Florida | Rakov V.A.,University of Florida
Journal of Geophysical Research: Atmospheres

We examined data on 117 return strokes in 31 rocket-and-wire-triggered lightning flashes acquired during experiments conducted from 1999 through 2004 at the International Center for Lightning Research and Testing at Camp Blanding, Florida, in order to compare the peak currents of the lightning return strokes with the corresponding charges transferred during various time intervals within 1 ms after return stroke initiation. We find that the determination coefficient (R2) for lightning return stroke peak current versus the corresponding charge transfer decreases with increasing the duration of the charge transfer starting from return stroke onset. For example, R2 = 0.91 for a charge transfer duration of 50 s after return stroke onset, R 2 = 0.83 for a charge transfer duration of 400 s, and R2 = 0.77 for a charge transfer duration of 1 ms. Our results support the view that (1) the charge deposited on the lower portion of the leader channel determines the current peak and that (2) the charge transferred at later times is increasingly unrelated to both the current peak and the charge deposited on the lower channel section. Additionally, we find that the relation between triggered-lightning peak current and charge transfer to 50 s in Florida is essentially the same as that for subsequent strokes in natural lightning in Switzerland, further confirming the view that triggered-lightning strokes are very similar to subsequent strokes in natural lightning. Copyright 2010 by the American Geophysical Union. Source

Gao W.,University of Denver | Ning J.,Enernex Corporation
IEEE Transactions on Smart Grid

This paper proposes a wavelet-based method to obtain the characteristics of frequency and voltage derivatives for disturbance analysis. Frequency and voltage derivatives are important indicators to reflect the degree of disturbances and manifest power system dynamics. However, current computational methods for the indicators have noticeable drawbacks with respect to the accuracy. Wavelet transform-based multiresolution analysis (WT-based MRA) is introduced to obtain the characteristics of the indicators by computed maximum wavelet coefficients (WCs). Results from numerical experiments show a superior performance of WT-based MRA over the existing methods. Generation loss and load change as two major types of disturbances are studied to verify the proposed method. The disturbances are simulated in PSS/E for IEEE New England 39-bus system. The relationship of maximum WCs and power variation is discussed. Maximum WCs can provide enough information to distinguish the location of generation loss and estimate the load power variation. © 2010 IEEE. Source

Ning J.,Enernex Corporation | Wang J.,Argonne National Laboratory | Gao W.,University of Denver | Liu C.,Argonne National Laboratory
IEEE Transactions on Smart Grid

This paper proposes a wavelet-based data compression approach for the smart grid (SG). In particular, wavelet transform (WT)-based multiresolution analysis (MRA), as well as its properties, are studied for its data compression and denoising capabilities for power system signals in SG. Selection of the Order 2 Daubechies wavelet and scale 5 as the best wavelet function and the optimal decomposition scale, respectively, for disturbance signals is demonstrated according to the criterion of the maximum wavelet energy of wavelet coefficients (WCs). To justify the proposed method, phasor data are simulated under disturbance circumstances in the IEEE New England 39-bus system. The results indicate that WT-based MRA can not only compress disturbance signals but also depress the sinusoidal and white noise contained in the signals. © 2010 IEEE. Source

Muljadi E.,National Renewable Energy Laboratory | Samaan N.,Pacific Northwest National Laboratory | Gevorgian V.,National Renewable Energy Laboratory | Li J.,Enernex Corporation | Pasupulati S.,Oak Creek Energy Systems Inc.
IEEE Transactions on Industry Applications

A wind power plant (WPP) consists of a large number of turbines interconnected by underground cable. A pad-mounted transformer at each turbine steps up the voltage from a generating voltage (690 V) to a medium voltage (34.5 kV). All turbines in the plant are connected to the substation transformer, where the voltage is stepped up to the transmission level. An important aspect of WPP impact studies is to evaluate the short-circuit (SC) current contribution of the plant into the transmission network under different fault conditions. This task can be challenging to protection engineers due to the topology differences between different types of wind turbine generators and the conventional generating units. This paper investigates the SC behavior of a WPP for different types of faults. The impact of wind turbine types, the transformer configuration, and the reactive compensation capacitor will be investigated. The voltage response at different buses will be observed. Finally, the SC line currents will be presented along with its symmetrical components. © 1972-2012 IEEE. Source

Todeschini G.,Enernex Corporation | Emanuel A.E.,Worcester Polytechnic Institute
IEEE Transactions on Energy Conversion

This paper details the transient operation of a wind energy conversion system (WECS) used simultaneously as an active filter and power generator. This study is intended to address the system response to two types of transient phenomena: voltage dips (fast transients) and wind speed variations (slow transients). The system response to voltage dips is governed by the electrical system dynamics and control method and results in the evaluation of the WECS low-voltage ride through capability. The study of the system response to wind speed variations requires a complete mechanical model to be included. Simulation results are presented for a typical WECS, and a discussion is carried out dealing with the generalization of the present work to other configurations. © 2010 IEEE. Source

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