Review Of Modern Diagnostic Techniques For Assessing Insulation Condition In Aged Transformers

Cellulosic paper and oil insulation in a transformer degrade at higher operating temperatures. Degradation is accelerated in the presence of oxygen and moisture. Power transformers being expensive items need to be carefully monitored throughout its operation. Well established time-based maintenance and conservative replacement planning is not feasible in a current market driven electricity industry. Condition based maintenance and online monitoring are now gaining importance. Currently there are varieties of chemical and electrical diagnostic techniques available for insulation condition monitoring of power transformers. This paper presents a description of commonly used chemical diagnostics techniques along with their interpretation schemes. A number of new chemical techniques are also described in this paper. In recent times a number of electrical diagnostic techniques have gained exceptional importance to the utility professionals. Among these techniques, polarisation/depolarisation current measurement, return voltage measurement and frequency domain dielectric spectroscopy at low frequencies are the most widely used. This paper describes analyses and interpretation of these techniques for transformer insulation condition assessment

Stewarding 2,4-D- and dicamba- based weed control technologies in cotton and soybean production systems

Distinguishing 2,4-D and dicamba herbicide formulations in cotton and soybean tissue is challenging in regulation of crop injury from these herbicides. Additionally, stewardship of 2,4-D and dicamba technologies is important to maximize their longevity and efficacy. Research was conducted to (1) characterize cotton and soybean response to various formulations of 2,4-D or dicamba with or without glyphosate, (2) develop a method for classifying these formulations in crop tissue, and (3) optimize use of chloroacetamide herbicides in dicamba systems for mitigation of selection pressure on dicamba. Formulations evaluated include dicamba diglycolamine (DGA), dimethylamine (DMA), N,N-Bis-(3-aminopropyl) methylamine (BAPMA), and DGA plus potassium acetate (KAc); and 2,4-D DMA, acid, isooctyl ester (ESTER), and choline. Weed management by the chloroacetamides s-metolachlor and acetochlor was evaluated with applications preemergence (PRE), early postemergence (EP), late postemergence (LP), PRE followed by (fb) EP, PRE fb LP, and EP fb LP. Cotton and soybean response differed by 2,4-D and dicamba formulation, and glyphosate presence. Cotton yield was reduced by 200 to 500 kg ha-1 following exposure to 2,4-D choline or DMA relative to acid or ESTER. Glyphosate presence led to a reduction in cotton and soybean yield of 377 and 572 kg ha-1, respectively. Exposure to dicamba DMA resulted in a 263 kg ha-1 reduction in soybean yield relative to dicamba DGA, and glyphosate presence reduced yield by 439 and 246 kg ha-1 in cotton and soybeans, respectively. Chemometric analyses generated models capable of up to 85% accuracy in identifying dicamba formulation in cotton and soybean tissue, and up to 80% accuracy in identifying 2,4-D formulation. Split chloroacetamide applications improved cotton yield up to 60%, reduced weed densities up to 90%, and improved control up to 56% relative to single applications. Cotton height was reduced up to 23% if a single chloroacetamide application was made. Soybean yield was maximized following any chloroacetamide application timing except PRE alone, and weed control was reduced up to 31% following single chloroacetamide application relative to split applications. These results will aid regulatory bodies in managing use of new weed control technologies and will assist producers in stewarding these new technologies

Furan measurement in transformer oil by UV-Vis spectroscopy using fuzzy logic approach

An Ultraviolet to Visible (UV-Vis) spectroscopic analysis based on fuzzy logic approach has been developed for furan content measurement in transformer oil. Following the successful identification and quantification of furan derivatives in transformer oil by ASTM D5837 standard, the new approach is able to approximate the furan content more conveniently and economically. As furan concentration level would determine the absorption intensity in UV-Vis spectral range, the fuzzy logic software model developed would exploit this characteristic to aggregate the furans content level in transformer oil. The UV-Vis spectral response at other ambient temperature is also studied. The proposed technique provides a convenient alternative to conventional method of furan measurement by High Performance Liquid Chromatography (HPLC) or Gas Chromatography Mass Spectrometry (GC/MS) in ASTM D5837 Standard

Erfassung und Evaluierung von Teilentladungen in Leistungstransformatoren mit speziellen Sensoren und Diagnoseverfahren

Transformers are key elements of the power grid. Due to their importance and high initial cost, asset managers utilize monitoring and diagnostic tools to optimize their operation and extend their service life. The main objective of this thesis is to develop new methods in the field of monitoring and diagnosis of transformers in order to reduce maintenance costs and decrease the frequency of forced outages. For this purpose, two concepts are proposed. Small generator step-up transformers are essential in wind and photovoltaic parks. The first presented concept entails an online fault gas monitoring system for these transformers, specially hermetically-sealed transformers. The developed compact, maintenance-free and cost-effective monitoring system continuously tracks the level of the key leading indicators of transformer faults in the gas cushion. The second presented concept revolves around partial discharge (PD) assessment by the UHF measurement technique, which is based on capturing the electromagnetic (EM) waves emitted in case of PD in the insulation of a transformer. In this context, the complex EM system established when probes are introduced into the tank of a transformer and with PD as the excitation source is analyzed. Drawing on this foundation, a practical approach to the detection and classification of PD with the focus on the selection of the optimal frequency range for performing UHF measurements depending on the device under test is presented. The UHF measurement technique also offers the possibility of PD localization. Here, the determined arrival time (AT) of the captured signals is critical. A PD localization algorithm, based on a multi-data-set approach with a novel AT determination method, is proposed. The methods and algorithms proposed for the detection, classification and localization of PD are validated by means of practical experiments

Commercial Systems for the Direct Detection of Explosives (for Explosive Ordnance Disposal Tasks)

The main goal of this study, carried out by the author on behalf of the Swiss Defence Procurement Agency (DPA), was to characterise existing technologies, and identify corresponding commercially available systems, for the direct detection of explosives for Explosive Ordnance Disposal (EOD) tasks. Systems should be able to determine if a given piece of munition contains explosives or is inert, and ideally in the former case to establish the type of explosive (see also Annex A2.1). This will be often referred to in the following as the “task at hand”, or the “task of interest to us”. Note that the object in questions has already been detected by other means (usually visually, e.g. lying on the surface) – what is needed is the capacity to characterise its contents (explosive or inert)

Monitoring Aspergillus Flavus Progression and Aflatoxin Accumulation in Inoculated Maize (Zea Mays L.) Hybrids

Aflatoxins are a secondary metabolite produced by the fungus Aspergillus flavus. A. flavus has been known to infect several crops including tree nuts, peanuts, rice, cotton and maize. Aflatoxins have been found to cause tumors with aflatoxin B1 being the most carcinogenic biologically produced substance known to man. Therefore, the FDA has restricted the amount of aflatoxin in maize for human consumption to 20 ppb (ng/g). An estimated $225 million are lost each year in the United States due to aflatoxin contamination in maize crops alone. Agriculture is a vital part of Mississippi’s economy, and maize is one of its largest crops. The purpose of this research is to track the correlations between aflatoxin accumulation and Aspergillus flavus fungal biomass for the first several weeks after inoculation, as well as the spreading of the fungus and the aflatoxin throughout the inoculated ear of maize. This will allow for better understanding of the pathogen-host interactions and how the fungus progresses over time. GA209 x T173 is the aflatoxin accumulation susceptible maize hybrid, GA209 x Mp313E is the susceptible and resistant hybrid, and Mp717 x Mp313E is the resistant maize hybrid to aflatoxin accumulation. These maize hybrids were each inoculated with toxin producing Aspergillus flavus NRRL 3357 and water as a control 21 days after silk maturation. Collections of the inoculated maize cobs were made 3, 7, 14, 21, 28, 35, and 60 days after inoculation. Maize samples were collected and analyzed for aflatoxin and DNA concentration. The extracted aflatoxin was analyzed using an LC/MS. The fungal biomass was determined by performing quantitative real time polymerase chain reaction (PCR). GA209xT173 and Mp717xMp313E showed no aflatoxin production two days after inoculation. The resistant maize hybrid lead in aflatoxin accumulation the last two years but had the least amount of fungal biomass for second and third years of the experiment The production of aflatoxin seems to begin decelerating after 21 days after inoculation. Resistance characteristics are more to prevent fungal infection. Fungal biomass was significantly higher in the susceptible hybrid GA209xT173 compared to the other hybrids. However, fungal spread was significantly higher in Mp313ExT173 and Mp717xMp313E

Fourier Transform Photoacoustic Spectroscopy with Broadband Lasers

Kaasujen havainnointi on merkittävässä roolissa kestävän, terveellisen ja turvallisen yhteiskunnan luomisessa. Lukuisten eri sovelluskohteiden vaatimukset kaasujen havainnointiin vaihtelevat valtavasti, ja siksi useita erityyppisiä sensoreita tarvitaan. Tämä väitöskirja edistää tätä tavoitetta esittelemällä uuden optisen kaasujen havainnointitekniikan, valoakustisen Fourier-muunnosspektroskopian laajakaistaisella keski-infrapunalaserilla ja herkällä läppämikrofonilla. Tekniikan merkittävimmät hyödyt ovat laajan, ainoastaan valonlähteen rajoittaman spektrisen kaistan nopea mittaus sekä herkkyyden tehokas parantaminen valonlähteen tehoa kasvattamalla. Tässä väitöskirjassa käytettyjen valonlähteiden, superjatkumon ja optisen taajuuskamman hyöty suuren optisen tehotiheyden lisäksi on korkea paikkakoherenssi, joka mahdollistaa erinomaisen spektrisen resoluution sekä tehokkaan kytkennän moniläpäisykammioon. Tekniikan suorituskyky on erinomainen vaadittavan näytetilavuuden ollessa alle kymmenen millilitraa. Metaanin havaintoraja viiden sekunnin mittausajalla on 90 miljardisosaa, jota voidaan parantaa merkittävästi keskiarvoistamalla. Korkein demonstroitu spektrinen resoluutio on 0.013 cm−1, joka ei heikennä systeemin herkkyyttä ja jota rajoittaa paineleveneminen. Kaksi kertaluokkaa huonompi spektrinen resoluutio kuitenkin mahdollistaa jo hyvän selektiivisyyden monen kaasun samanaikaiseen havainnointiin. Hyvän suorituskyvyn ja pienen näytetilavuuden ainutlaatuisen yhdistelmän ansiosta tekniikka on potentiaalinen esimerkiksi haihtuvien yhdisteiden ja saatavuudeltaan rajoitettujen näytteiden analysoimiseen. Eräs potentiaalinen ja tässä väitöskirjassa demonstroitu sovelluskohde on kemiallisten taisteluaineiden havaitseminen rikostutkinnassa ja jatkuvatoimisissa varoitusjärjestelmissä. Lähitulevaisuudessa sekä tekniikan suorityskyvyn että sovellettavuuden odotetaan kehittyvän merkittävästi, mikä vahvistaa tekniikan asemaa vaihtoehtona teollisiin, lääketieteellisiin ja turvallisuussovelluksiin.Gas sensing plays a key role in the progress towards a healthier, safer and more sustainable society. The amount of gas sensing applications are immense with varying requirements, and thus numerous sensors with different characteristics are needed. This thesis contributes to the task by introducing a new optical gas sensing technique, Fourier transform photoacoustic spectroscopy (FT-PAS) implemented with a spectrally broadband mid-infrared laser and a sensitive cantilever microphone. The main benefits of FT-PAS are the fast acquisition of a wide spectral range that is only limited by the light source, and the effective enhancement of sensitivity with a high-power light source. Two light sources are demonstrated in this thesis, namely an incoherent fiber-based supercontinuum and a frequency down-converted mode-locked optical frequency comb. Besides high power spectral density, the advantage of broadband lasers stems from their high spatial coherence enabling high spectral resolution and efficient coupling to multipass cells. The performance of cantilever-enhanced FT-PAS is excellent while requiring a sample volume of less than ten milliliters. The detection limit for methane is 90 parts per billion in five seconds, which can be significantly lowered through longer averaging. The highest demonstrated spectral resolution is 0.013 cm−1 with no compromise in the detection sensitivity and limited by pressure broadening. However, two orders of magnitude worse spectral resolution already provides sufficient selectivity for complex multi-species detection. The unique combination of high performance and low gas consumption makes the technique attractive for the analysis of volatile substances and samples with limited availability. The detection of chemical warfare agents for forensic crime scene investigation and online warning systems is one potential application of the technique demonstrated in this thesis. In the near future, both the performance and the applicability of FT-PAS are expected to remarkably improve, establishing the technique as a notable alternative in many industrial, medical and security applications

Commercial Systems for the Direct Detection of Explosives (for Explosive Ordnance Disposal Tasks)

There are a number of Explosive Ordnance Disposal (EOD) tasks in which it is necessary to discriminate and identify UneXploded Ordnance (UXO) already detected by other means. What we seek is the capacity to characterize in a non-destructive way the munition?s content, usually either explosive or inert (e.g., practice munition), if possible using a fairly mobile system and without direct contact. A number of existing technologies for the direct detection of explosives, applicable in EOD scenarios, are therefore characterized, and corresponding commercially available systems or advanced prototypes identified whenever possible. Some of the techniques are also useful for the detection of buried UXO or landmines, to which we refer whenever appropriate. We first concentrate on bulk explosive detection, in particular on neutron based systems exploiting gamma spectroscopy, which have the potential of detecting the explosive?s nitrogen content and/or its other constituents (carbon, oxygen and hydrogen). Candidate systems exist, although most of them have as primary aim the discrimination of chemical munition. We then describe the application of trace explosive detection techniques, which seems to be less mature also due to the large number of parameters influencing the variables of interest (explosive vapor and particle concentration). Sampling is in this case of primary importance

LOLA: Lunar Optical Long-baseline Array. 1992-1993 space design

In the fall of 1992, the design and analysis of a lunar-based optical interferometer telescope array was initiated by a group of students in the Department of Aerospace Engineering at Virginia Tech. This project was undertaken at the suggestion of the Space Exploration Initiative Office at the NASA Langley Research Center. The original array design requirements, listed below, centered on the primary objective of resolving earth-type planets about stars out to a distance of ten parsecs: spectrum coverage spanning wavelengths from five nm to five mm, with a primary operating mode in the visible spectrum; a total collecting area providing a signal-to-noise ratio (SNR) of no less than 10.0 for a median wavelength of 500 nm; the individual array elements must be identical and have a maximum optical diameter of 2.0 m; and lunar site selection is limited to ten degrees north and south of the lunar equator on the lunar far side while not closer than 15 degrees to either near-side limb. Following construction by astronaut crews, array operation will be conducted from earth and astronomical observations will not be conducted during the lunar day. The entire system is designed for minimum achievable mass. The majority of the original design requirements for the telescope array were met