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NASA NTRS1976

Estimated transonic flying qualities of a tailless airplane based on a model investigation, 8 June 1949

Flying qualities of a tailless airplane with the wing quarter chord line swept back 35 deg were analyzed in the Mach number range from 0.40 to 0.91 based on tests of a model of this airplane in the Langley high speed 7 by 10 foot tunnel. The results indicate that longitudinal control position instability exists at transonic speeds but the accompanying trim changes are not large. Control position maneuvering stability, however, is present for all speeds. Longitudinal and lateral control appear adequate, but the damping of the short period longitudinal and lateral oscillations at high altitudes is poor and would probably require artificial damping.

Donlan, C. J.↗

DOE OSTI2016

Broad Balmer absorption line variability: Evidence of gas transverse motion in the QSO SDSS J125942.80+121312.6

We report on the discovery of broad Balmer absorption lines variability in the QSO SDSS J125942.80+121312.6, based on the optical and near-infrared spectra taken from the SDSS-I, SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS), and TripleSpec observations over a timescale of 5.8 years in the QSO's rest-frame. The blueshifted absorption profile of Hβ shows a variation of more than 5σ at a high velocity portion (>3000 km s{sup −1}) of the trough. We perform a detailed analysis for the physical conditions of the absorber using Balmer lines as well as metastable He i and optical Fe ii absorptions (λ4233 from b{sup 4}P{sub 5/2} level and λ5169 from a{sup 6}S{sub 5/2}) at the same velocity. These Fe ii lines are identified in the QSO spectra for the first time. According to the photoionization simulations, we estimate a gas density of n(H)≈10{sup 9.1} cm{sup −3} and a column density of N{sub col}(H)≈10{sup 23} cm{sup −2} for the BOSS data, but the model fails to predict the variations of ionic column densities between the SDSS and BOSS observations if changes in ionizing flux are assumed. We thus propose transverse motion of the absorbing gas being the cause of the observed broad Balmer absorption line variability. In fact, we find that the changes in covering factors of the absorber can well-reproduce all of the observed variations. The absorber is estimated ∼0.94 pc away from the central engine, which is where the outflow likely experiences deceleration due to the collision with the surrounding medium. This scheme is consistent with the argument that LoBAL QSOs may represent the transition from obscured star-forming galaxies to classic QSOs.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2018

High-energy spin fluctuation in low-Tc iron-based superconductor LaFePO0.9

Spin fluctuations are widely believed to play an important role in the superconducting mechanisms of unconventional high temperature superconductors. Spin fluctuations have been observed in iron-based superconductors as well. However, in some iron-based superconductors such as LaFePO 0.9 , they have not been observed by inelastic neutron scattering (INS). LaFePO 0.9 is an iron-based superconductor with a low superconducting transition temperature ( T c = 5 K), where line nodes are observed in the superconducting gap function. The line-node symmetry typically originates from sign reversal of the order parameter in spin-fluctuation-mediated superconductivity. This contradiction has been a long-standing mystery of this superconductor. Herein, spin fluctuations were found at high energies such as 30–50 meV with comparable intensities to an optimally doped LaFeAs(O, F). Based on this finding, the line-node symmetry can be explained naturally as spin-fluctuation-mediated superconductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2025

Decision-Dependent Uncertainty-Aware Distribution System Planning Under Wildfire Risk

The interaction between power systems and wildfires can be dangerous and costly. Distribution grids can be liable for the outbreak of wildfires during extreme weather. In wildfire-prone areas, investment planning should consider the impact of operational actions on wildfire-related uncertainties affecting line failure likelihood. Here, in this case, endogenous-based uncertainty modeling should comprise the backbone of the investment planning model viz-a-viz the inability of standard exogenous-based uncertainty modeling. Therefore, we propose a decision-dependent uncertainty (DDU) aware methodology to optimize investment portfolios for distribution systems, considering that high power-flow levels in high-threat areas can ignite wildfires and increase line failure probability. The methodology identifies the best combination of upgrades (new lines, hardening existing lines, and placing switching devices). Methodologically, we propose a two-stage distributionally robust planning optimization problem with DDU that considers the distribution system's multiperiod operation. The first stage determines optimal switching actions and line investments, and the second stage evaluates the worst-case expected operational cost under a DDU framework designed to account for the endogenous impact of power-flow levels and hardening investment decisions in the line failure probabilities. An iterative method is tailored to handle the problem and numerical experiments demonstrate a more prepared grid to deal with wildfire risk.

Power systems investment planning↗

DOE OSTI2024

Zone plate-based extreme ultraviolet mask microscope with through-pellicle imaging capability

Mirror-based and zone plate-based imaging systems are being used in actinic extreme ultraviolet (EUV) reticle review tools. With regard to zone plates, a short working distance is advantageous in terms of the required spectral bandwidth, manufacturability, and potential throughput and imaging performance. Zone plates therefore typically have a short working distance. The industry has adopted the use of an EUV pellicle to protect the photomask. Imaging photomask through-pellicle requires a working distance larger than 2.5 mm. A zone-plate-based EUV mask microscope with a 3-mm working distance has been commissioned at beamline 11.3.2 of the Advanced Light Source. Through-pellicle imaging at an exposure time of 2 s is demonstrated. The instrument achieves an image contrast of 95% on large features on a photomask with a tantalum-based absorber. Imaging down to 45-nm half pitch (mask scale) is demonstrated. A NILS of 2.55 is achieved on 60-nm half-pitch (mask scale) lines and spaces. These results demonstrate that zone-plate-based imaging systems can meet the requirements of an actinic EUV mask review tool in terms of imaging performance and throughput in an instrument compatible with EUV pellicles.

Extreme ultraviolet↗

NASA NTRS1978

Interpretation of Beta Lyrae. IV - Hydrogen emission profiles and the pattern of gaseous flow in the system

The paper presents an interpretation of hydrogen emission profiles found in Beta Lyrae by attributing the asymmetry of the two emission peaks of both H-alpha and H-gamma at different phases to the absorption of an expanding-rotating gaseous stream. It is proposed that different relative shifts of the absorption line with respect to the emission line exist at different phases resulting in an apparent change in the profile with phase. Based on this idea, the expected profiles at four different phases have been computed for the H-alpha and H-gamma lines. They show a general trend close to what has been observed. Based on this same idea an apparent discrepancy between the observed results of the H-gamma profile obtained at two different epochs about 15 years apart becomes understandable. Finally a physical picture that can produce this periodic shift of the emission line relative to the absorption line is proposed and discussed.

Huang, S.-S.↗

DOE OSTI2015

Radio pulsar death lines to SGRs/AXPs and white dwarfs pulsars

Recently, an alternative model based on white dwarfs pulsars has been proposed to explain a class of pulsars known as Soft Gamma Repeaters (SGR) and Anomalus X-Ray Pulsars (AXP) [1], usually named as magnetars. In this model, the magnetized white dwarfs can have surface magnetic field B ∼ 10{sup 7} − 10{sup 10} G and rotate very fast with angular frequencies Ω ∼ 1 rad/s, allowing them to produce large electromagnetic (EM) potentials and generate electron-positron pairs. These EM potentials are comparable with the ones of neutron star pulsars with strong magnetic fields and even larger. In this study we consider two possible processes associated with the particle acceleration, both of them are common used to explain radio emission in neutron star pulsars: in the first process the pair production happens near to the star polar caps, i.e. inside of the light cylinder where magnetic field lines are closed; in the second one the creation of pair happens in the outer magnetosphere, i.e. far away of the star surface where magnetic field lines are open [2]. The analysis of the possibility of radio emission were done for 23 SGRs/AXPs of the McGill Online Magnetar Catalog [3] that contains the current information available on these sources. The results of this work show that the model where the particles production occur in the outer magnetosphere emission “o2” is the process compatible with the astronomical observations of absence of radio emission for almost all SGRs/AXPs when these sources are understood as white dwarf pulsars. Our work is a first attempted to find an explanation for the puzzle why for almost all the SGRs/AXPs was expected radio emission, but it was observed in only four of them. These four sources, as it was suggested recently [4], seem to belong to an high magnetic field neutron star pulsar category, different from all the others SGRs/AXPs that our work indicate to belong to a new class of white dwarf pulsars, very fast and magnetized.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2022

Detection of innate immune response modulating impurities (IIRMI) in therapeutic peptides and proteins: Impact of excipients

Unintended immunogenicity can affect the safety and efficacy of therapeutic proteins and peptides, so accurate assessments of immunogenicity risk can aid in the selection, development, and regulation of biologics. Product- and process- related impurities can act as adjuvants that activate the local or systemic innate immune response increasing the likelihood of product immunogenicity. Thus, assessing whether products have innate immune response modulating impurities (IIRMI) is a key component of immunogenicity risk assessments. Identifying trace levels of individual IIRMI can be difficult and testing individually for all potential impurities is not feasible. Therefore, to mitigate the risk, cell-based assays that use human blood cells or monocyte-macrophage reporter cell lines are being developed to detect minute quantities of impurities capable of eliciting innate immune activation. As these are cell-based assays, there is concern that excipients could blunt the cell responses, masking the presence of immunogenic IIRMI. Here, we explore the impact of frequently used excipients (non-ionic detergents, sugars, amino acids, bulking agents) on the sensitivity of reporter cell lines (THP-1- and RAW-Blue cells) and fresh human blood cells to detect purified TLR agonists as model IIRMI. We show that while excipients do not modulate the innate immune response elicited by TLR agonists in vivo, they can impact on the sensitivity of cell-based IIRMI assays. Reduced sensitivity to detect LPS, FSL-1, and other model IIRMI was also evident when testing 3 different recombinant drug products, product A (a representative mAb), B (a representative growth factor), C (a representative peptide), and their corresponding formulations. These results indicate that product formulations need to be considered when developing and validating cell-based assays for assessing clinically relevant levels of IIRMI in therapeutic proteins. Optimization of reporter cells, culture conditions and drug product concentration appear to be critical to minimize the impact of excipients and attain sensitive and reproducible assays.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2021

Smartphone-based Dual-channel Immunochromatographic Test Strip with Polymer Quantum Dot Labels for Simultaneous Detection of Cypermethrin and 3-phenoxybenzoic acid

Currently, gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS) are the primary methods used to detect pesticides and their metabolites for biomonitoring of exposure. Although GC-MS and LC-MS can provide accurate and sensitive measurements, these techniques are not suitable for point-of-care or in-field biomonitoring applications. The objective of this work is to develop a smartphone-based dual-channel immunochromatographic test strip (ICTS) for on-site biomonitoring of exposure to cypermethrin by simultaneous detection of cypermethrin and its metabolite, 3-phenoxybenzoic acid (3-PBA). Polymer carbon dots (PCDs) with ultra-high fluorescent brightness were synthesized and used as signal amplifier in ICTS assay. Cypermethrin (a representative pyrethroid pesticide) and its major metabolite 3-PBA were simultaneously detected to provide more comprehensive analysis of cypermethrin exposure. After competitive immunoreactions between the target sample and the coating antigens preloaded on the test line, the tracer antibody (PCDs conjugated antibody) was quantitatively captured on the test lines. The captured PCDs were inversely proportional to the amount of the target compound in sample. The red fluorescence on the test line then was recorded by a smartphone-based device capable of conducting image analysis and recording. Under optimal conditions, the sensor showed excellent linear responses for detecting cypermethrin and 3-PBA ranging from 1 ng/mL to 100 ng/mL and from 0.1 ng/mL to 100 ng/mL, the limits of detection were calculated to be ~0.35 ng/mL for cypermethrin and ~0.04 ng/mL for 3-PBA, respectively. The results demonstrate that the ICTS device is promising for accurate point-of-care biomonitoring of pesticide exposure.

Zhao, Yuting↗

DOE OSTI2016

T24 HRAS transformed NIH/3T3 mouse cells (GhrasT-NIH/3T3) in serial tumorigenic in vitro/in vivo passages give rise to increasingly aggressive tumorigenic cell lines T1-A and T2-A and metastatic cell lines T3-HA and T4-PA

Cancer cells often arise progressively from “normal” to “pre-cancer” to “transformed” to “local metastasis” to “metastatic disease” to “aggressive metastatic disease”. Recent whole genome sequencing (WGS) and spectral karyotyping (SKY) of cancer cells and tumorigenic models have shown this progression involves three major types of genome rearrangements: ordered small step-wise changes, more dramatic “punctuated evolution” (chromoplexy), and large catastrophic steps (chromothripsis) which all occur in random combinations to generate near infinite numbers of stochastically rearranged metastatic cancer cell genomes. This paper describes a series of mouse cell lines developed sequentially to mimic this type of progression. This starts with the new GhrasT-NIH/Swiss cell line that was produced from the NIH/3T3 cell line that had been transformed by transfection with HRAS oncogene DNA from the T24 human bladder carcinoma. These GhrasT-NIH/Swiss cells were injected s.c. into NIH/Swiss mice to produce primary tumors from which one was used to establish the T1-A cell line. T1-A cells injected i.v. into the tail vein of a NIH/Swiss mouse produced a local metastatic tumor near the base of the tail from which the T2-A cell line was established. T2-A cells injected i.v. into the tail vein of a nude NIH/Swiss mouse produced metastases in the liver and one lung from which the T3-HA (H=hepatic) and T3-PA (P=pulmonary) cell lines were developed, respectively. T3-HA cells injected i.v. into a nude mouse produced a metastasis in the lung from which the T4-PA cell line was established. PCR analysis indicated the human T24 HRAS oncogene was carried along with each in vitro/in vivo transfer step and found in the T2-A and T4-PA cell lines. Light photomicrographs indicate that all transformed cells are morphologically similar. GhrasT-NIH/Swiss cells injected s.c. produced tumors in 4% of NIH/Swiss mice in 6–10 weeks; T1-A cells injected s.c. produced tumors in 100% of NIH/Swiss mice in 7–10 days. T1-A, T-2A, T3-HA and T4-PA cells when injected i.v. into the tail produced local metastasis in non-nude or nude NIH/Swiss mice. T4-PA cells were more widely metastatic than T3-HA cells when injected i.v. into nude mice. Evaluation of the injected mice indicated a general increase in metastatic potential of each cell line in the progression as compared to the GhrasT-NIH/3T3 transformed cells. A new photomicrographic technique to follow growth rates within six preselected 2×2 mm{sup 2} grids per plate is described. Average doubling times of the transformed cells GhrasT-NIH/3T3 (17 h), T1A (17.5 h), T2A (15.5 h), T3-HA (17.5 h) and T4-PA (18.5 h) (average 17.2 h) were significantly faster (P=0.006) than NIH Swiss primary embryonic cells and NIH/3T3 cells (22 h each). This cell series is currently used in this lab for studies of cancer cell inhibitors, mitochondrial biogenesis and gene expression and is available for further study by other investigators for intra- and inter-laboratory comparisons of WGS, transcriptome sequencing, SKY and other analyses. The genome rearrangements in these cells together with their phenotypic properties may help provide more insights into how one tumorigenic progression occurred to produce the various cell lines that led to the highly metastatic T4-PA cell line. - Highlights: • A tumor progression model derived from a new T24 HRAS transformed NIH/3T3 cell line. • T1-A, T2-A, T3-HA, T4PA lines derived from GhrasT-NIH/3T3, T1-A, T2-A, T3-HA tumors. • PCR detected the human HRAS oncogene in T2-A and T4-PA metastatic tumors. • These five new cell lines showed a progressive increase in tumorigenic potential. • New method obtained doubling times using daily photomicrographs of gridded plates.

60 APPLIED LIFE SCIENCES↗

NASA NTRS2003

Obliquity Driven Climate Change in Mars' Recent Past

We use the NASA/Ames grid Mars general circulation model with an updated radiation code and cloud nlicrophysics scheme. To speed up the simulations, we run the model at fairly coarse resolution (7.5" latitude x 22.5" longitude). Radiation Code Fluxes and heating rates are calculated from a radiation code based on the two-stream solution to radiative transfer that fully accounts for multiple scattering in the presence of gaseous absorp- tion. The model has 12 spectral intervals. Dust and water ice scattering properties are included. For dust, we use the Ockert-Bell [9] values in the visible, and Forget [IO] values in the infrared. For ice, we can either compute them online as the cloud evolves, or we can specify them. Gaseous opacities for water vapor and CO2 are calculated from correlated k-distributions taken from full line-by-line models. Cloud Microphysics Our cloud scheme is based on momentlorder scheme in which the mass mixing ratio and number density of the cloud ensemble are the advected species. From these we obtain a mean particle size and an estimate or the particle size distribution assuming a variance) which we then divide into 8 bins. Cloud microphysics is performed in each of these bins and includes nucleation, condensation, and gravitational settling. Dust is treated as a tracer and serves as condensation nuclei. The altered size distribution is then converted back into a mean size, a mixing ratio, and a particle number density.

Haberle, R. M.↗

NASA NTRS1990

Collecting, analyzing and archiving of ground based infrared solar spectra obtained from several locations

The infrared solar spectrum as observed from the ground under high resolution contains thousands of absorption lines. The majority of these lines are due to compounds that are present in the Earth's atmosphere. Ground based infrared solar spectra contain information concerning the composition of the atmosphere at the time the spectra were obtained. The objective of this program is to record solar spectra from various ground locations, and to analyze and archive these spectra. The analysis consists of determining, for as many of the absorption lines as possible, the molecular species responsible for the absorption, and to verify that current models of infrared transmission match the observed spectra. Archiving is an important part of the program, since a number of the features in the spectra have not been identified. At some later time, when the features are identified, it will be possible to determine the amount of that compound that was present in the atmosphere at the time the spectrum was taken.

Murcray, David G.↗

DOE OSTI2024

Advanced Energy Scale Correction Techniques for the X-ray Transition Edge Sensors of the Athena mission

The X-ray Integral Field Unit (X-IFU) onboard the future European X-ray telescope Athena will be the first space instrument carrying an array of more than a thousand transition edge sensors. One of the key challenges of the X-IFU is the measurement of narrow X-ray atomic lines to determine velocity shifts at an unprecedented level of accuracy. For this reason, the energy scale of the instrument needs to be known with extreme accuracy, of 0.4 eV (1σ) up to 7 keV. The energy scale will be measured on the ground through a dedicated calibration campaign using fiducial X-ray sources. Though calibrated, the energy scale is extremely sensitive to the environmental conditions around the TES array, and drifts in the readout chain electronics. Uncorrected, the energy scale can naturally drift up to hundreds of eVs. Changes of the TES gain will be monitored via onboard X-ray calibration sources, and the energy scale will be corrected either per pixel, or within a small groups of pixels. Although simulations show that a 0.4 eV level can be achieved, the very high accuracy required by the X-IFU calls for experimental validation. A dedicated measurement campaign has been performed by NASA Goddard Space Flight Center to characterize the energy scale of a prototype kilo-pixel array of X-IFU-representative TESs. The analysis of the data demonstrated the ability to correct for various drifts using two fiducial lines to track the temporal gain variation. In this paper, we propose to extend this study on the same data set by investigating multi-parameter correction techniques based on both the pulse-height of the fiducial line and the prepulse baseline level, using the knowledge of the TES energy scale at reference temperature/magnetic field set points acquired on the ground. Investigations on the co-adding of pixels to perform a joint correction over pools of pixels is also explored.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1997

The Need for V&V in Reuse-Based Software Engineering

V&V is currently performed during application development for many systems, especially safety-critical and mission-critical systems. The V&V process is intended to discover errors, especially errors related to entire' domain or product line rather than a critical processing, as early as possible during the development process. The system application provides the context under which the software artifacts are validated. engineering. This paper describes a framework that extends V&V from an individual application system to a product line of systems that are developed within an architecture-based software engineering environment. This framework includes the activities of traditional application-level V&V, and extends these activities into the transition between domain engineering and application engineering. The framework includes descriptions of the types of activities to be performed during each of the life-cycle phases, and provides motivation for activities.

Addy, Edward A.↗

NASA NTRS2002

Deuterium Abundance Toward G191-B2B: Results from the Far Ultraviolet Spectroscopic Explorer (FUSE) Mission

High-resolution spectra of the hot white dwarf G191-B2B covering the wavelength region 905-1187A were obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE). This data was used in conjunction with existing high-resolution Hubble Space Telescope STIS observations to evaluate the total H(sub I), D(sub I), O(sub I) and N(sub I) column densities along the line of sight. Previous determinations of N(D(sub I)) based upon GHRS (Goddard High Resolution Spectrograph) and STIS (Space Telescope Imaging Spectrograph) observations were controversial due to the saturated strength of the D(sub I) Lyman alpha line. In the present analysis the column density of D(sub I) has been measured using only the unsaturated Lyman beta and Lyman gamma lines observed by FUSE. A careful inspection of possible systematic uncertainties tied to the modeling of the stellar continuum or to the uncertainties in the FUSE instrumental character series has been performed. The column densities derived are: log N(D(sub I)) = 13.40+/-0.07, log N(O(sub I)) = 14.86+/-0.07, and log N(N(sub I)) = 13.87+/-0.07 quoted with 2sigma, uncertainties. The measurement of the H(sub I) column density by profile fitting of the Lyman alpha line has been found to be unsecure. If additional weak hot interstellar components are added to the three detected clouds along the line of sight, the H(sub I)) column density can be reduced quite significantly, even though the signal-to-noise ratio and spectral resolution at Lyman alpha are excellent. The new estimate of N(H(sub I)) toward G191-B2B reads: logN(H (sub I)) = 18.18+/-0.18 (2sigma uncertainty), so that the average (D/H) ratio on the line of sight is: (D/H)= 1.66(+0.9/-0.6) x 10(exp -5) (2sigma uncertainty).

Lemoine, M.↗

NASA NTRS1981

On the relationship between soft X-rays and H-alpha-emitting structures during a solar flare

Based on data obtained during a solar flare on March 31, 1979, soft X-ray (SXR) and hard X-ray (HXR) bursts are analyzed and compared with other available data in order to identify structures in H-alpha that may correspond to the SXR-emitting site. Measurements taken with the X-ray telescope and the XUV spectroheliograph flown on Skylab, have shown that the SXR emission from many flares comes from rather small structures of about 10-20 arcsec across. These structures appear to be loops that cross the magnetic neutral line. Understanding of the morphology of SXR was based on data of the solar flare of June 15, 1973, observed from Skylab, and the work of Moore et al., (1980). Dense, highly emissive coronal structures, not suggested to be the X-ray source, were forming, lost energy rapidly by emission and conduction, and finally formed the loops. It is concluded that bright H-alpha loops form rapidly as the SXR emission rises, and the overall decay (cooling rate) of SXR emission is much slower than the formation time of individual loops.

Zirin, H.↗

DOE OSTI2019

Fast magnetic reconnection and the ideal evolution of a magnetic field

Regardless of how small non-ideal effects may be, phenomena associated with changes in magnetic field line connections are frequently observed to occur on an Alfvénic time scale. Since it is mathematically impossible for magnetic field line connections to change when non-ideal effects are identically zero, an ideal evolution must naturally lead to states of unbound sensitivity to non-ideal effects. That such an evolution is natural is demonstrated by the use of Lagrangian coordinates based on the flow velocity of the magnetic field lines. The Lagrangian representation of an evolving magnetic field is highly constrained when neither the magnetic field strength nor the forces exerted by the magnetic field increase exponentially with time. The development of a state of fast reconnection consistent with these constraints (1) requires a three-dimensional evolution, (2) has an exponentially increasing sensitivity to non-ideal effects, and (3) has a parallel current density, which lies in exponentially thinning but exponentially widening ribbons, with a magnitude that is limited to a slow growth. The implication is that exponential growth in sensitivity is the cause of fast magnetic reconnection when non-ideal effects are sufficiently small. The growth of the non-ideal effect of the resistivity multiplied by the parallel current density is far too slow to be competitive.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2019

Impedance-Based Prediction of SSR-Generated Harmonics in Doubly-Fed Induction Generators: Preprint

Doubly-fed induction generators (DFIGs) are prone to subsynchronous resonance (SSR) with series-compensated transmission lines and experiencing SSR-generated harmonics of wide-ranging magnitudes. This paper presents a large-signal impedance-based approach for the prediction of the magnitude of SSR-generated harmonics in DFIGs. Note that the large-signal impedance of a network shows the variation in its impedance response with the magnitude of perturbation at its terminals. It is discovered in this paper that the impedance of a series-compensated transmission line starts changing with the magnitude of SSR because of the metal oxide varistor (MOV) based protection of series capacitors in the line. The changing line impedance locks the growth of SSR beyond a certain point, where the DFIG forms a limit cycle mode and emits harmonics at the SSR frequency. The discovered role of the protection of series-capacitors in SSR not only enables the prediction of the SSR-generated harmonics but it can also be used for the timely detection of an SSR event to avoid system disruption and sudden loss of a bulk generation. The large-signal impedance-based prediction of SSR-generated harmonics in DFIG-based wind and hydro generators is demonstrated using numerical simulations of a 2.5-MW, 690-V DFIG supplying to a series-compensated transmission line.

24 POWER TRANSMISSION AND DISTRIBUTION↗