This study presents a new resistive capacitor switching transient limiter (RCSTL) for mitigating power capacitor switching transients. The RCSTL is composed of three limiting resistors, a three-phase ...full bridge diode rectifier, a thyristor and a three-phase coupling transformer. The limiting resistors are connected in series with the capacitor bank and the thyristor is installed at the DC side of the diode rectifier. During the capacitor bank energising, the thyristor remains off and hence, the secondary side of the coupling transformer acts as open circuit. Consequently, high impedance including the transformer's magnetic reactance in parallel with the limiting resistors is inserted in series with the capacitor bank. Under such circumstance, the limiting resistors restrain the capacitor switching transients. In the steady-state, the control system triggers the thyristor and the coupling transformer acts as short circuit. As a result, the limiting resistors are bypassed by the coupling transformer and thus, the RCSTL has no significant effect on the circuit. Analytical analysis is performed to describe different operation modes of the proposed RCSTL. A single stage of a three-phase wye-connected capacitor bank with 25 kVAR is energised and the performance of the proposed limiter is investigated. Both the simulation and experimental results confirm the effectiveness of the RCSTL.
This paper presents the use of pulse-width modulated voltage source converter (PWM-VSC) for power quality improvement of a wound field synchronous generator-based diesel generator (DG) set realising ...standalone supply system. The system consists of a diesel engine driven wound field synchronous generator, a three-leg PWM-VSC with a capacitor on the DC link and linear/non-linear loads. The PWM-VSC supplies the leading kilo volt-amphere reactive (kVAR) to the loads and maintains the unity power factor of the DG set. In addition, it eliminates the harmonics from the source currents and provides load balancing. The terminal voltage is controlled by field excitation control of the generator and the supply frequency is controlled by the speed regulating system of the diesel engine. A variable step size filter-x least mean square-based control algorithm is used for estimation of reference currents for control of VSC.
This paper presents an active Fault Tolerant Control (FTC) strategy for induction motor (IM) that ensures Field Oriented Control (FOC) and offset the effect of the sensor faults despite of the load ...torque disturbance. The proposed approach uses a fuzzy descriptor approach to estimate simultaneously the system state and the sensor fault. The physical model of IM is approximated by the Takagi-Sugeno (T-S) fuzzy technique in the synchronous d-q rotating frame with field-oriented control strategy. The stability conditions are analyzed using Lyapunov theory. The controller and observers gains are calculated by solving a set of Linear Matrix Inequalities (LMIs). Finally, the effectiveness of the proposed strategy have been illustrated in simulation and experimental results.
In this paper first a current predictive method for single open-phase fault detection in a three phase drive with a permanent magnet synchronous machine is presented. The proposed method is based on ...a predictive stator current calculation. For each sampling interval the difference between the actual stator current and its predicted value in a previous sampling interval is calculated. To identify the location of a single open-phase fault, an identification method is presented which is based on the analysis of the stator current vector angle. After the single open-phase fault is detected and identified it is desirable for the electrical machine to continue operating with a reduced number of phases. For this purpose, a modified direct torque control algorithm for the fault-tolerant control is implemented. In order to improve the performance of the drive, a pre-firing angle is additionally introduced. All proposed methods have been simulated in Matlab/Simulink and verified on an experimental model.
Faults of wind turbine generator electromechanical parts are common and very expensive. This paper introduces a generator fault-tolerant control scheme for variable-speed variable-pitch wind turbines ...that can be applied regardless to the AC generator used. The focus is on generator stator isolation inter-turn fault that can be diagnosed and characterised before triggering the safety device. An extension of the conventional wind turbine control structure is proposed that prevents the fault propagation while power delivery under fault is deteriorated as less as possible compared to healthy machine conditions. Fault-induced and inherent asymmetries of the generator are estimated and respected by the field-oriented control of the generator to eliminate torque oscillations. An approach for asymmetry detection based on an unscented Kalman filter is proposed. Presented fault-tolerant control strategy is developed taking into account its modular implementation and installation in available control systems of existing wind turbines to extend their exploitable life span and increase energy production. Simulation results for the case of a megawatt class wind turbine are presented.
Članak analizira ležajeve kao najučestalije uzroke kvarova u rotacijskoj, strojarskoj i električnoj opremi te kao uzroke eksplozija u industrijskim postrojenjima u kojima se pojavljuje eksplozivna ...atmosfera plinova, para i prašine. Prikazane su razdiobe učestalosti kvarova u rotacijskoj opremi i razdiobe učestalosti eksplozija, odnosno uzroka paljenja eksplozivne atmosfere u kontekstu kritičkog ispitivanja današnje metodologije protueksplozijske zaštite. Prezentirane razdiobe učestalosti kvarova u strojarskoj i električnoj opremi te uzročnika paljenja eksplozivne atmosfere temelje se na podacima prikupljenim u raznim industrijskim postrojenjima s eksplozivnom atmosferom.
U radu je dan pregled stanja visokonaponskih prekidača i rastavljača
ugrađenih u elektrovučnim podstanicama u vlasništvu HŽ Infrastrukture.
Prikazan je način održavanja prekidača i rastavljača prema ...trenutačno
važećim HŽI-ovim internim aktima i preporukama proizvođača. Prikazani
su kvarovi na prekidačima i rastavljačima u razdoblju od 2014. do 2018.
godine. Dan je prikaz kvarova po pojedinim rasklopnim aparatima te
prikazano vrijeme potrebno za otklanjanje kvara. Također je dan popis
elektrovučnih podstanica u kojima je zbog dotrajalosti potrebno zamijeniti
rasklopne aparate.
Cilj istraživanja: Odrediti preciznost vizualne procjene oštećenja rotirajućih i recipročnih endodontskih instrumenata vizualno i optičkim pomagalima. Materijal i postupci: Istraživanje su provela ...četiri ispitivača podijeljena u dvije dobne skupine: 1. skupina od 20 do 30 godina - n = 2 i 2. skupina od 40 do 50 godina - n = 2. Vizualno su procijenili postoje li oštećenja rotirajućih ili recipročnih endodontskih instrumenata samo okom i dvjema vrstama optičkih pomagala. Svaki ispitivač pregledao je ukupno 239 instrumenata različitih proizvođača. Svi su kalibrirali oko na novom instrumentu prije procjene oštećenja. Osjetljivost metode procjene obavljena je golim okom. Kada je instrument okom procijenjen kao oštećen, procjena je prekinuta te se instrument i dvjema drugim metodama procjene smatrao oštećenim. Rezultati: Pronađeno je oštećenje na 178 instrumenata. Osjetljivost procjene oštećenja okom iznosi 49,7 %, za povećala 66,2 %, a za operacijski mikroskop 76,5 %. Trima metodama procjene oštećenja dobivene su značajne razlike u osjetljivosti (p < 0,05). Zaključak: Zaključeno je da postoji značajna razlika između dobnih skupina u procjeni oštećenja instrumenta. Također je uočeno da se razlikuje procjena oštećenja samo okom i optičkim pomagalima. Konačno, kad je riječ o lakoći prepoznavanja oštećenja, pronađene su značajne razlike između različitih strojnih endodontskih instrumenata. No ni jedna vrsta instrumenta nije bila sklonija oštećenjima od drugih.
U članku je prikazan jedan analitički postupak određivanja momenata, odnosno intervala vremena između mjerenja vitalnih karakteristika uređaja u cilju utvrđivanja momenta nastupanja kvara, tako da ...maksimalna relativna greška, učinjena pri tom, bude konstantna pri bilo kojem mjerenju. Ovaj postupak odnosi se na slučaj kada se mjerenja na uređaju ne obavljaju kontinuirano, već se vrše povremeno.
U radu se razmatraju rizici pojave uzročnika paljenja unutar elektromotora u prostorima ugroženim eksplozivnom atmosferom. Istraživanje pojave uzročnika paljenja zbog oštećenja kaveza rotora ...asinkronog motora temeljni je dio ovog rada. Istraživana su zagrijavanja kaveza rotora protueksplozijski zaštićenog "Ex e" motora kod različitih razina oštećenja. Ispitivanjima je potvrđena pretpostavka da bi određeni kvarovi kaveza rotora mogli biti djelotvorni uzročnici paljenja. Rezultatima istraživanja produbljene su spoznaje o mogućnostima i rizicima pojavljivanja uzročnika paljenja eksplozivne atmosfere stvaranjem vrućih površina zbog kvarova u kavezu rotora. Spoznaja da tradicionalni pristup analize protueksplozijske zaštite nije dostatan za otkrivanje spomenutih kvarova važan je rezultat ovog rada.
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