Power Quality Problems Due to Transformer Inrush Current

Transformer energization can produce a large nonsinuoidal inrush current which contains both odd and higher order harmonic components that can put transformer winding under mechanical stress. Additionally, they can cause irregular tripping of harmonic protection relays. Furthermore, in relatively weak power systems, such as is the Bosnian system, the superposition of harmonic components with system resonance frequencies may produce temporary overvoltages (TOV). Transformer winding failures and metal oxide surge arrester (MOA) energy stresses can occur due to TOV. The paper demonstrates a case study of an energization of a 220/110 kV transformer and power quality problems that can appear due to higher harmonics. Energy stresses of MOA provoked by transformer energization are considered in the paper

THE NUMERICAL CALCULATION OF LOW FREQUENCY ELECTROMAGNETIC TRANSIENT PHENOMENA IN POWER TRANSFORMERS

U radu je predstavljen model transformatora primjenjiv u niskofrekvencijskim elektromagnetskim prijelaznim pojavama, frekvencija reda oko 1 kHz. Analiziran je primjer uklapanja neopterećenog energetskog transformatora. Prvo je pokazan pojednostavljeni analitički pristup, a zatim, zbog njegova ograničenja, u analizu je uveden numerički pristup rješavanja krutih diferencijalnih jednadžbi koje opisuju prijelaznu pojavu. U oba slučaja je realiziran algoritam za generiranje valnih oblika varijabli stanja. Rezultati oba algoritma su uspoređeni s rezultatima MATLAB/Simulink/Power System Blockset, namjenskog programa za analizu elektromagnetskih prijelaznih pojava u elektroenergetskom sustavu. Razvijeni algoritam se može uspješno koristiti u ostalim niskofrekvencijskim prijelaznim pojavama gdje je glavni predmet analize nelinearni karakter transformatora: ferorezonancija, ispad tereta, kvarovi kod transformatora itd. Na kraju su pokazane usporedbe mjerenih i simuliranih struja uklapanja trofaznog trostupnog transformatora.In this article, a transformer model is presented that is applicable to low frequency electromagnetic transient phenomena of up to 1 kHz. An example of the energization of a no-load transformer is analyzed. A simplified analytical approach is presented first. Due to the limitations of this approach, a numerical approach is introduced for the solution of the stiff differential equations that describe the transient phenomena. In both cases, algorithms have been developed for generating the waveforms of the state variables. The results of both algorithms are compared to the results of the MATLAB/Simulink/Power System Blockset for the analysis of electromagnetic transient phenomena in electrical energy systems. Developed algorithm with the introduced numerical approach can be used successfully in other low frequency transient phenomena where the main subject of analysis is the nonlinear character of the transformer: ferroresonance, load switch-off, transformer faults etc. Finally, a comparison is made between the measured and simulated inrush currents of a three-phase three-legged transformer

SUGAR BEET ROOT YIELD AND QUALITY DEPENDENT ON DIGGING TIME AND HYBRID SELECTION

Istraživanja prinosa i kvalitete korijena 38 sorata šećerne repe ovisno o roku vađenja obavljena su 2006. godine na dvije lokacije, Topolje i Seleš. U Topolju su bila dva pokusa i to jedan gdje je korištenjem fungicida lišće repe u vegetaciji očuvano i drugi, uz jako oštećenje lišća od bolesti C. beticola Sacc. budući da fungicidi nisu korišteni. U Selešu je bio jedan pokus i to uz zaštitu šećerne repe fungicidima. Vađenje repe u prvom roku obavljeno je 13. i 14. rujna, a u drugom 34 dana kasnije (18. i 19. listopada). Vremenske prilike između dva termina vađenja karakterizirao je manjak oborina u usporedbi s višegodišnjim prosjekom, što je pozitivno utjecalo na jesenski porast i tehnološko sazrijevanje korijena šećerne repe. Produženje vegetacije za 34 dana, u drugom roku vađenja, kod pokusa očuvanog lišća (uz primjenu fungicida), u prosjeku za dvije lokacije, dovelo je do povećanja prinosa korijena za 9,75 t/ha, odnosno 11,34%, sadržaja šećera za 0,79% i prinosa čistog šećera za 2,17 t/ha. Iz toga proizlazi da je u drugoj polovini rujna i prvoj polovini listopada dnevno po 1 ha povećan prinos korijena za 287 kg, sadržaj šećera za 0,02% i prinos čistog šećera za 63,8 kg/ha. U pokusu uz oštećenje lišća (bez primjene fungicida) dnevni porast korijena je iznosio 217 kg/ha, odnosno 7,39 t/ha za 34 dana. Međutim, sadržaj šećera nije povećan, već, naprotiv, smanjen za 0,08%. Uz to je povećan i udio topivih nešećera (K, Na, AmN), čime je povećan šećer u melasi, što je dovelo do smanjenja iskorištenja šećera. U ovom pokusu za 34 dana duže vegetacije prinos šećera je povećan 0,94 t/ha (8,47%), dnevno samo 27,6 kg/ha. Osjetne razlike u prinosu utvrđene su i između sorata. Prema tome, preporuka i težnja da se šećerna repa vadi što kasnije ima opravdanja samo uz zdravo i očuvano lišće, birajući adekvatne sorte.Studies of root yield and quality of 38 sugar beet hybrids were carried out depending on digging time on two locations, in Topolje and Seleš. Two trials were done in Topolje, one with application of fungicides that preserved sugar beet leaves in vegetation period, another, with recorded heavy damage (no fungicide applied) on sugar beet leaves by C. beticola Sacc. disease. Trial with fungicides provided protection was conducted in Seleš. Sugar beet digging in the first period was done on 13th and 14th September, and 34 days later in the second period (18th and 19th October). Weather conditions between the terms of digging were characterized by shortage in precipitation when compared to the multiyear average, which influenced autumn growth and technological maturation of sugar beet root. Prolonged vegetation period for 34 days in the second term of digging in the trial with leaves preserved (fungicide application) for two locations on the average resulted in root yield increase by 9.75 t/ha i.e. 11.34%, sugar content by 0.79% and pure sugar yield by 2.17 t/ha. Consequently, in the second half of September and the first half of October root yield was daily increased by 278 kg/ha, sugar content by 0.02 % and pure sugar yield by 63.8 kg/ha. The trial with leaves damaged (no fungicide application) had daily root growth of 217 kg/ha i.e. 7.39 t/ha in 34 days. However, sugar content was not increased, but lowered by 0.08%. In addition, the rate of soluble non-sugars (K, Na, AmN) was increased which made values of sugar in molasses higher giving rise to the decrease in sugar utility. In this trial with 34 days prolonged vegetation period, sugar yield was increased by 0.94 t/ha (8.47%), daily only 27.6 kg/ha. Considerable differences in yield were also determined between these hybrids. Therefore, recommendation, and intention for sugar beet digging as later as possible, can be justified only with health and preserved sugar beet leaves, selecting adequate hybrids

EVALUATION OF ENERGY STRESS ON LINE ARRESTERS

Line Surge Arresters (LSAs) are efficient means for the improvement of the lightning performance of transmission lines. Determination of optimal LSA number, location and rating is important for the improvement of the reliability and availability of a transmission system. In selection of the LSA special attention should be paid to their energy stress which depends on complex interactions between the arrester locations, grounding, shielding and the local lightning environment. LSAs experience higher energy stress compared to station arresters, because the incoming surge to a station is limited by insulator flashover on the transmission line and impulse corona. In this paper calculations of energy stresses were carried out for a double-circuit 220 kV line with a single shielding wire. Parametric studies were conducted in which arrester discharge energy was a function of: time to half value of stroke current, number of towers with arresters, footing resistance, span length and angle of power frequency voltage. Arrester energy stress is analyzed in case of stroke to tower and shielding failure. From conducted analysis it can be concluded that energy stress on LSAs is lower for shorter span lengths. Tower footing resistance has only minor effect on the discharge energy. Arrester discharge energy strongly depends on time to half of the stroke current, number of towers with installed arresters and angle of power frequency voltage

IMPORTANCE OF SORT SELECTION AND FUNGICIDES APPLICATION IN CERCOSPORA BETICOLA SACC. SUGAR BEET LEAF SPOT PREVENTION AND QUALITY ROOT HIGH YIELD ACHIEVEMENT

Vrijednost sorata šećerne repe te njihova tolerantnost prema uzročniku pjegavosti lišća (Cercospora beticola Sacc.) istraživana je u uvjetima prirodne infekcije bez i uz primjenu fungicida, tijekom dvije godine (2004., 2005.), na dvije lokacije (Topolje, Seleš). Vrednovanje sorata šećerne repe izvršeno je preko pokazatelja prinosa i kvalitete korijena te prinosa čistog šećera, kao i vizualnom ocjenom oštećenja listova. U istraživanje je uključeno 26 sorata koje se koriste u širokoj proizvodnji ili se njihovo uvođenje očekuje. Istraživane sorte pokazale su nedovoljnu tolerantnost prema gljivi C. beticola Sacc. pa je primjenom fungicida u odnosu na netretirane pokuse povećan prosječni prinos korijena za 11,07 t/ha (14,8%), sadržaj šećera za 1,00% (rel. 7,1%) te prinos čistog šećera za 2,08 t/ha (23,0%). Na pokusima uz primjenu fungicida najveći prosječni prinos korijena postigla je sorta Libero (98,49 t/ha), najveću digestiju Iris 16,23%) i najveći prinos šećera sorta Merak (12,67 t/ha).Sugar beet hybrids value as well as their tolerance to the leaf spot agent (Cercospora beticola Sacc.) were researched in the natural infection conditions with and without fungicides application on two locations (Topolje, Seleš) in the two year period (2004, 2005). Evaluation has been done via root yield and quality, sugar yield as well as visual leaf damage estimation. The research comprised 26 sorts as either widely used in practice or to be introduced. The investigated sorts showed insufficient tolerance to C. beticola Sacc. Thus, fungicide application, compared to untreated trials, resulted in increased mean root yield by 11.07 t/ha (14.8%), sugar content by 1.00% (relative 7.1%) and sugar yield by 2.08 t/ha (23.0%). The trials with fungicide application were characterized by the highest mean root yield obtained with the Libero hybrid (98.49 t/ha), sugar concentration with the Iris sort (16.23%) and sugar yield with the Merak hybrid (12.67 t/ha)

Study of interstrip gap effects and efficiency for full energy detection of Double Sided Silicon Strip Detectors

In this work is reported a study on the response of double sided silicon strip detectors. In order to investigate the effect of the electrode segmentation on the detector response, two experiments were performed aimed to measure the efficiency for full energy detection. Results show that the efficiency for full energy detection, that is directly related to effective width of the inter-strip region, varies with both detected ion energy and bias voltage. The experimental results are qualitatively reproduced by a simplified model based on the Shockley-Ramo-Gunn framework

Experimental study of high-lying states in ²⁸Mg using the resonant elastic scattering of α particles

International audienceThe excitation function of Mg28 above the α-decay threshold has been measured for the first time using the resonant scattering of α particles with the technique of a thick target in inverse kinematics. Thirteen new states are reported between Ex=15.5 and Ex=20.5 MeV, and suggestions for spin-parity assignments are given for two of these. Calculations of the branching ratio to α decay for these states as well as comparison of the measured cross sections to calculations suggest that α+Neg.s.24 clustering is not dominant in this energy regime

Mass correlation between light and heavy reaction products in multinucleon transfer 197Au+130Te collisions

We studied multinucleon transfer reactions in the 197Au+130Te system at Elab=1.07 GeV by employing the PRISMA magnetic spectrometer coupled to a coincident detector. For each light fragment we constructed, in coincidence, the distribution in mass of the heavy partner of the reaction. With a Monte Carlo method, starting from the binary character of the reaction, we simulated the de-excitation process of the produced heavy fragments to be able to understand their final mass distribution. The total cross sections for pure neutron transfer channels have also been extracted and compared with calculations performed with the grazing code

Structure of 24Mg excited states and their influence on nucleosynthesis

The main idea of the two presented experiments is to study the decay of resonances in 24Mg at excitation energies above the 12C+12C decay thresh- old, in the astrophysical energy region of interest. The measurement of the 12C(16O,α)24Mg* reaction was performed at INFN-LNS in Catania. Only the α+20Ne decay channel of 24Mg is presented here, because it was a motivation for conducting a new experiment, a study of the 4He(20Ne,4He)20Ne reaction, performed at INFN-LNL in Legnaro. Some preliminary results of this measurement are also presented

Light and heavy fragments mass correlation in the 197Au+130Te transfer reaction

We studied multinucleon transfer (MNT) processes in the 197Au+130Te at Elab=1.07 GeV system coupling the PRISMA magnetic spectrometer to NOSE, an ancillary particle detector. We constructed a mass correlation matrix associating to each light fragment identified in PRISMA the corresponding mass distribution of the heavy partner detected in NOSE and, through the comparison with Monte Carlo simulations, we could infer about the role of neutron evaporation in multinucleon transfer reactions for the population of neutron-rich heavy nuclei