Search results for "disc"
showing 10 items of 19256 documents
Restricted compositions and permutations: from old to new Gray codes
2011
Any Gray code for a set of combinatorial objects defines a total order relation on this set: x is less than y if and only if y occurs after x in the Gray code list. Let @? denote the order relation induced by the classical Gray code for the product set (the natural extension of the Binary Reflected Gray Code to k-ary tuples). The restriction of @? to the set of compositions and bounded compositions gives known Gray codes for those sets. Here we show that @? restricted to the set of bounded compositions of an interval yields still a Gray code. An n-composition of an interval is an n-tuple of integers whose sum lies between two integers; and the set of bounded n-compositions of an interval si…
Statistics-preserving bijections between classical and cyclic permutations
2012
Recently, Elizalde (2011) [2] has presented a bijection between the set C"n"+"1 of cyclic permutations on {1,2,...,n+1} and the set of permutations on {1,2,...,n} that preserves the descent set of the first n entries and the set of weak excedances. In this paper, we construct a bijection from C"n"+"1 to S"n that preserves the weak excedance set and that transfers quasi-fixed points into fixed points and left-to-right maxima into themselves. This induces a bijection from the set D"n of derangements to the set C"n"+"1^q of cycles without quasi-fixed points that preserves the weak excedance set. Moreover, we exhibit a kind of discrete continuity between C"n"+"1 and S"n that preserves at each s…
Measurements on partial discharge in on‐site operating power transformer: a case study
2018
This study presents the case study of a substation in-service power transformer referred to the on-site partial discharge (PD) detection and evaluation methods. An original methodology for simultaneous application of three methods is proposed: electrical, acoustic and ultra-high frequency. Transformer is powered by the power grid and no external generator is required according to the proposed methodology. Furthermore, several possibilities of applying these concurrent measurements and benefits of such solution in terms of result interpretation, interference resistance and on-site measurement applicability are indicated. The proposed methodology allows for a fast, accurate and secure PD diag…
A New Approach to Partial Discharge Detection Under DC Voltage: Application to Different Materials
2021
Usability of a new Direct Current Periodic waveform for partial discharge qualification in HVDC systems is exemplified by tests performed on different materials.
Partial discharges behavior under different rectified waveforms
2017
In this work, a previous software used to simulate partial discharges (PDs) under Alternating Current (AC) stress has been modified in order to evaluate the PDs behavior under a voltage stress close to the Direct Current (DC) waveform. By using a full-wave and a half-wave rectifier, the specimen with an air void defects has been subjected to a gradual constant stress. Finally, a capacitive filter has been inserted in order to produce a steadier voltage supply. Simulation results show that under an almost DC waveform, the PDs activity become less compared to AC stress.
The Use of Two-Diode Substitute Model in Predicting the Efficiency of PV Conversion in Low Solar Conditions
2017
Abstract The article presents theoretical foundations of a two-diode equivalent model of a photovoltaic cell/module (PV), together with calculation procedures. A physical interpretation of individual components of an equivalent model was presented. Its practical application in predicting efficiency of operation of various PV cells and modules in low insulation conditions was demonstrated. The obtained predictions were verified with the actual results of their operation in open space (outdoor). The practical suitability of the “model” in early detection of ageing phenomena, such as, for example, absorber degradation taking place in PV modules, was demonstrated. The article was prepared on th…
Photovoltaics: solar energy resources and the possibility of their use
2016
Abstract In this paper possibilities and limits of use of solar energy (like the best efficiencies of PV cells, world records and ‘notable exceptions’) were shown. Also some new ideas and concepts in photovoltaics (like new photovoltaic power plants or energy storage) were presented. Additionally authors try to predict development of solar power industry.
PD characteristics at Square Shaped Voltages Applying Two Different Detecting Techniques
2016
Nowadays power electronic converters are widely used and the fast switching voltage fronts results in an increased stress on the insulation material and may cause a reduction of the HV systems reliability. Nonsinusoidal voltage waveform have influence on the partial discharges (PD) characteristics in insulating systems due to the increased harmonic content which causes problems mainly in electrical PD measurement setups. In fact, impulse voltages cause strong switching disturbances, which make it much more difficult to distinguish PD signals from noise. This work investigates the influence of repetitive steep pulses on different types of test objects exposed to square wave voltages applying…
Partial discharges at different voltage waveshapes: Comparison between two different acquisition systems
2018
In modern HV apparatuses the wide use of electronic converters, increase the stress on the involved insulation systems and thus affect the reliability of the whole power grid. Additionally, such non-sinusoidal voltage shapes contain high gradient flanks that create problems in the detection of partial discharge (PD) activity. The aim of this paper is to discuss the methodology on how to suitably approach PD detection in insulation systems exposed to various voltage waveshapes in general by comparing two different measuring systems. The first one, equipped with a resonant PD decoupler, designed specifically for detection at typical power electronic waveshapes and the other one, based on an a…
High-frequency electrodeless lamps in argon–mercury mixtures
2005
In this paper, numerical and experimental investigations of high-frequency (HF) electrodeless lamps in argon–mercury mixtures are performed. The intensities of the mercury spectral lines having wavelengths λ = 404.66, 435.83, 546.07 nm (7 3S1–6 3P0,1,2) and the resonance line λ = 253.7 nm (6 3 P1–6 1S0) are measured at a wide range of mercury pressures, varying the HF generator current and argon filling pressure. A stationary self-consistent model of HF electrodeless discharge lamp is developed including kinetics of the excited mercury and argon atomic states. Based on the developed model, the radiation characteristics of the discharge plasma are calculated. Numerical simulation of the line…