Abstract: Current collection quality is one of the limiting factors when increasing trains movement speed in the rail sector. With the movement speed growth, the impact forces on the current collector from the rolling stock and the aerodynamic influence increase, which leads to the spread in the contact pressure values, separation of the current collector head from the contact wire, contact arcing and excessive wear of the contact elements. The upcoming trend in resolving this issue is the use of the automatic control systems providing stabilization of the contact pressure value. The present paper considers the features of the contemporary automatic control systems of the current collector’s pressure; their major disadvantages have been stated. A scheme of current collector pressure automatic control has been proposed, distinguished by a proactive influence on undesirable effects. A mathematical model of contact strips wearing has been presented, obtained in accordance with the provisions of the central composition rotatable design program. The analysis of the obtained dependencies has been carried out. The procedures for determining the optimal current collector pressure on the contact wire and the pressure control principle in the pneumatic drive have been described.
Abstract: Insulators are one of the most significant equipment in power system. The insulators’ operation may affect the power flow, line loss and reliability. The electrical parameters that influence the performance of insulator are surface leakage current, corona and dry band arcing. Electric field stresses on the insulator surface will degrade the insulating properties and lead to puncture. Electric filed stresses can be analyzed by numerical methods and experimental evaluation. As per economic aspects, evaluation by numerical methods are best. In outdoor insulation, a hydrophobic surface can facilitate to prevent water film formation on the insulation surface, which is decisive for diminishing leakage currents and partial discharge (PD) under heavy polluted environments and harsh weather conditions. Polymer materials like silicone rubber have an outstanding hydrophobic property among general insulation materials. In this paper, electrical field intensity of 220 kV porcelain and polymer double tension insulator strings at critical regions are analyzed and compared by using Finite Element Method. Hydrophobic conditions of polymer insulator with equal and unequal water molecule conditions are verified by using finite element method.
Abstract: High voltage insulator has to withstand sever electrical stresses. Higher electrical stresses lead to erosion of the insulator surface. Degradation of insulating properties leads to flashover and in some extreme cases it may cause to puncture. For analyzing these electrical stresses and implement necessary actions to diminish the electrical stresses, numerical methods are best. By minimizing the electrical stresses, reliability of the power system will improve. In this paper electric field intensity at critical regions of 400 kV silicone composite insulator is analyzed using finite element method. Insulator is designed using FEMM-2D software package. Electric Field Analysis (EFA) results are analyzed for five cases i.e., only insulator, insulator with two sides arcing horn, High Voltage (HV) end grading ring, grading ring-arcing horn arrangement and two sides grading ring. These EFA results recommended that two sides grading ring is better for minimization of electrical stresses and improving life span of insulator.
Abstract: Nowadays, the direct effects of lightning to aircrafts are of great importance because of the massive use of composite materials. In comparison with metallic materials, composites present several weaknesses for lightning strike direct effects. Especially, their low electrical and thermal conductivities lead to severe lightning strike damage. The lightning strike direct effects are burning, heating, magnetic force, sparking and arcing. As the problem is complex, we investigated it gradually. A magnetohydrodynamics (MHD) model is developed to simulate the lightning strikes in order to estimate the damages on the composite materials. Then, a coupled thermal-electrical finite element analysis is used to study the interaction between the lightning arc and the composite laminate and to investigate the material degradation.
Abstract: Dynamics of cathode spot has become a major part
of vacuum arc discharge with its high academic interest and
wide application potential. In this article, using a three-dimensional
statistical model, we simulate the distribution of the ignition
probability of a new cathode spot occurring in different magnetic
pressure on old cathode spot surface and at different arcing time.
This model for the ignition probability of a new cathode spot was
proposed in two typical situations, one by the pure isotropic random
walk in the absence of an external magnetic field, other by the
retrograde motion in external magnetic field, in parallel with the
cathode surface. We mainly focus on developed relationship between
the ignition probability density distribution of a new cathode spot and
the external magnetic field.
Abstract: One of the major developments in machine learning in the past decade is the ensemble method, which finds highly accurate classifier by combining many moderately accurate component classifiers. In this research work, new ensemble classification methods are proposed with homogeneous ensemble classifier using bagging and heterogeneous ensemble classifier using arcing and their performances are analyzed in terms of accuracy. A Classifier ensemble is designed using Radial Basis Function (RBF) and Support Vector Machine (SVM) as base classifiers. The feasibility and the benefits of the proposed approaches are demonstrated by the means of standard datasets of intrusion detection. The main originality of the proposed approach is based on three main parts: preprocessing phase, classification phase, and combining phase. A wide range of comparative experiments is conducted for standard datasets of intrusion detection. The performance of the proposed homogeneous and heterogeneous ensemble classifiers are compared to the performance of other standard homogeneous and heterogeneous ensemble methods. The standard homogeneous ensemble methods include Error correcting output codes, Dagging and heterogeneous ensemble methods include majority voting, stacking. The proposed ensemble methods provide significant improvement of accuracy compared to individual classifiers and the proposed bagged RBF and SVM performs significantly better than ECOC and Dagging and the proposed hybrid RBF-SVM performs significantly better than voting and stacking. Also heterogeneous models exhibit better results than homogeneous models for standard datasets of intrusion detection.
Abstract: The present work aims to throw light on the effects of
arcing in air on the surface state of contact pastilles made of silvernickel
Ag-Ni (60/40). Also, the photoelectric emission from these
electrical contacts has been investigated in the spectral range of 196-
256 nm. In order to study the effects of arcing on the EWF, the
metallic samples were subjected to electrical arcs in air, at
atmospheric pressure and room temperature, after that, they have
been introduced into the vacuum chamber of an experimental UHV
set-up for EWF measurements. Both Fowler method of isothermal
curves and linearized Fowler plots were used for the measurement of
the EWF by the photoelectric effect.
It has been found that the EWF varies with the number of applied
arcs. Thus, after 500 arcs in air, the observed EWF increasing is
probably due to progressive inclusion of oxide on alloy surface.
Microscopic examination is necessary to get better understandings on
EWF of silver alloys, for both virgin and arced electrical contacts.
Abstract: In the present work, an attempt has been made to
understand the feasibility of using UHF technique for identification
of any corona discharges/ arcing in insulating material due to water
droplets. The sensors of broadband type are useful for identification
of such discharges. It is realised that arcing initiated by liquid droplet
radiates UHF signals in the entire bandwidth up to 2 GHz. The
frequency content of the UHF signal generated due to corona/arcing
is not much varied in epoxy nanocomposites with different weight
percentage of clay content. The exfoliated/intercalated properties
were analysed through TEM studies. It is realized that corona
initiated discharges are of intermittent process. The hydrophobicity
of the material characterized through contact angle measurement. It
is realized that low Wt % of nanoclay content in epoxy resin reduces
the surface carbonization due to arcing/corona discharges. The results
of the study with gamma irradiated specimen indicates that contact
angle, discharge inception time and evaporation time of the liquid are
much lower than the virgin epoxy nanocomposite material.
Abstract: Power transformer consists of components which are
under consistent thermal and electrical stresses. The major
component which degrades under these stresses is the paper
insulation of the power transformer. At site, lightning impulses and
cable faults may cause the winding deformation. In addition, the
winding may deform due to impact during transportation. A
deformed winding will excite more stress to its insulating paper thus
will degrade it. Insulation degradation will shorten the life-span of
the transformer. Currently there are two methods of detecting the
winding deformation which are Sweep Frequency Response
Analysis (SFRA) and Low Voltage Impulse Test (LVI). The latter
injects current pulses to the winding and capture the admittance
plot. In this paper, a transformer which experienced overheating and
arcing was identified, and both SFRA and LVI were performed.
Next, the transformer was brought to the factory for untanking. The
untanking results revealed that the LVI is more accurate than the
SFRA method for this case study.