Daily Archives: 30 December 2018

An Improved Numerical Model of Heat Transfer Coefficient Corresponding to a Through Connector

Abstract

This paper is a continuation of a previous re-search in which was presented a method to determine heat transfer coefficient values corresponding to crimped connec-tions. Because the differences between numerical values of temperature obtained with a mathematical model for hΣ and experiments were high, authors considered that the model could be improved. Therefore, in the presented paper are shown the results obtained for heat transfer coefficient and temperature corresponding to crimped connections using an improved model. It was started from some values determi-nated previously and there were obtained new values of hΣ which can give the possibility to attain the temperature val-ues closed to experiments. The numerical model was devel-oped considered a coupled problem – Magnetic- Steady State Heat Transfer. Using iteration there were determined new values for heat transfer coefficient which gave the pos-sibility to find the Joule heat, heat flux and temperature distribution in the studied crimped connection. Thus, the numerical model can be used to determine the temperature values for several types of crimped connections with small errors. images

Diagnosis with Analytic Model of a Rectifier for Faults of the Rectifier Control

Abstract

The diagnosis of the electric systems is an actual item for the specialists in domain. Due to the variety of the measurements and multiplicity of faults which can be analyzed, the approach is motivating. The model reproduces the behavior of a system both in normal operation and fault occurrence. The procedure which uses the analytic models compares the system evolution in normal and fault conditions operation. The faults which affect the normal system operation can occur on the supplying side (grid faults), in the rectifier itself (one or more switches in fault), on the load side or in the control circuit of the rectifier. Authors had previously studied different faults within a controlled rectifier-DC motor system. The supplying side faults (broken phase, phase to ground and two phases short-circuit faults), interrupted or short-circuited switch within the rectifier and excitation disappearance were investigated. The paper deals with the analysis of different faults of the control circuit. The considered faults were the firing pulses lack for one switch or for the two switches on the same arm (phase). The effects on the rectifier operation (waveforms, major values) and on the load behavior are highlighted. As it is shown, the effects on the output waveforms of the two studied faults are quite different. images

Single/Three-Phase Transformer with Variable Frequency for Electric Locomotives

Abstract

Electric rail transport is positioned as environ-ment-friendly technology that has good future prospects for development. The supply of electric rail transport from DC or AC power lines requires the use of specialized transform-ers that form the three-phase system in the low-voltage cir-cuit to power this load. Solid State Transformer (SST) are very attractive for use in power systems of electric locomo-tives. This paper examines a new architecture for the reali-zation of SST transformers for their use in power systems of electric locomotives. The proposed SST transformer has the bidirectional high-frequency power transmission capability and at the same time ensures multiplication of phases in the low voltage circuit. The SST transformer is a single-phase / three-phase transformer, which can be supplied both from the high-voltage DC power network and from the AC net-work frequently used in electric rail transport. Changing the power supply type (of the current) does not lead to changes in the topology of the SST. The transformer is de-signed as an object made of identical functional modules. The ferromagnetic core is made of separate portions for each functional module. This simplifies the problem of en-suring the electrical stiffness of the transformer. The tran-sistors of the module operate at variable switching fre-quency, have soft switching mode. Energy conversion takes place in a single step. This ensures that losses are diminished and transformer efficiency is increased in all load regimes. Mathematical simulations have confirmed that this trans-former has a very low impact on the power supply, whether the power supply is DC or AC. Under-load operation of the SST transformer does not lead to pollution of the power supply network with higher current harmonics. images

Automatic Sorting and Handling Station Actuated by Pneumatic Drive

Abstract

The main path through which technical progress contributes to increasing work productivity is the automa-tion of manufacturing processes. Applications based on ro-botic handling solve many problems in different areas, espe-cially in the food, pharmaceutical, plastics, building materi-als, or logistics applications. The paper presents an auto-matic electro-pneumatic system for manipulation and sort-ing of parts according to color. The system is taught to sort two kinds of pieces, both white and black. Pieces of different types arrive at the input stock and are picked up by a ma-nipulating robot, then stored in two output stocks according to color. The entire structure is integrated in an electro-pneumatic drive system with linear actuators (pneumatic cylinder) and rotary (rotary pneumatic motors), controlled by the solenoid valves. The manipulator robot consists of three modules (rotation, lifting, gripper actuation), and the output stock contains a rotating module for the sorting table provided with two parts warehouses. Both white and black pieces will be stored in the two storehouses. The structure is controlled by an Arduino Mega2560 microcontroller devel-opment system. The sorting station can also be controlled by the operator via a joystick and some buttons. The system designed, developed and tested can be used both in educa-tional applications in electrical engineering and in industrial applications. In comparison to other handling systems, the robot structure is simpler. It performs the transfer of the pieces by only two movements, thus reducing the handling time. images

Analysis of Losses in Brushless Direct Current Motors and Their Influence upon Operation Characteristics

Abstract

Researches regarding the optimum design and construction of brushless direct current motors are very present, owing to their use in small-dimension vehicles (elec-trical scooter, electrical bicycle, motor-scooters, electrical vehicles for disabled passengers). Motors used in two-wheel or four-wheel conveyances are permanent magnet direct current motors, manufactured by brushless technology. The operation, starting and speed control characteristics of the brushless direct current motor designed must correspond to certain conditions of competitiveness and to high exigencies imposed by the complex equipments used in passenger-transport vehicles. The study carried out and the simula-tions presented aim at identifying the important losses in order to reduce them. The widespread use of command electronics associated with power components, in brushless direct current motors supply, enabled the optimization of their operation, with special performances. In this paper there is presented the revised computation relation for iron losses, known in design, by establishing separately the two components: hysteresis losses and eddy-current losses. This way, the efficiency obtained in the design stage gets close to the experimentally established efficiency, the error being less than 2%. images

Indirect Current Control Algorithm Implementation and Validation, for Active Filtering Using Constant Switching Frequency Hysteresis Controllers

Abstract

The aim of this paper is the implementation and the experimental validation of a constant switching fre-quency hysteresis current controller as a part of an active filtering system control algorithm, based on the indirect current control. The classical choices in the literature are the hysteresis current controller and the PI controller both with their corresponding advantages and disadvantages. A solution which achieves the advantages of both classical hysteresis and PI controllers is the constant switching fre-quency hysteresis current controller. This controller can be obtained by combining the hysteresis comparators with the PWM suboptimal modulator. The performances of the ac-tive filtering system based on the indirect current control and the proposed controller are compared with the corre-sponding performances obtained by the same system im-plemented with the well documented PI current controller. The regulator implementation and performance compara-tive study were accomplished on a comprehensive experi-mental active filtering system based on the dSpace DS1103 prototyping board. images

Analysis of the Phaseportrait for the Lü Dynamical System in a Particular Case

Abstract

In the present paper it is started a qualitative analysis of the Lü dynamical system, using the appropiate tools of Hamilton-Poisson geometry and using the software for mathematics MAPLE 15. The Lü’s system arise from electrical engineering networks and it is very known that he has a chaotic behavior. For this reason, the problem of finding the solution of the system could be very difficult. By obtaining of a geometric Hamilton-Poisson structure, we can find such a solution as the intersection of two surfaces, the surfaces equation being given by the Hamiltonian and the Casimir function . Using MAPLE 15, it will be analyzed the phase portrait for two particular simplified versions of the dynamical system associated to the Lü ordinary differential system (a=0, b=c=0 and a=1, b=c=0). Also, we will do a study of the Lyapunov stability of Lü’s system for the particular case (a=1, b=c=0). We obtain that the origin is an unstable equilibrium point for this particular parameter case of the Lü’s model. This fact is confirmed by the numerical simulations. More that, the pictures show that the origin is a non-stable focus, in the first simulation case. Analytical results are accompanied by numerical illustrations. images

Power line Compromising Emanations Analysis

Abstract

The paper presents an innovative method used to analyze the video-compromising signals that computer equipment generates during normal operation. It presents the measurement results achieved for conducted emissions for a commercial laptop using a shielded power source and a commercial transformer as well as conducted emissions generated by a display unit which is connected to a laptop and is alternatively powered by a commercial and a shielded cable. In order to perform these tests, there were selected several graphical images consisting of horizontal bars of various widths to facilitate the detection and evaluation of the compromising video signal level. images

Modeling Three-Phase Short-Circuits for Radial Distribution Systems

Abstract

Monitoring radial distribution systems in short-circuit conditions represents a quite important issue of elec-tric power networks supplied by renewable sources. The method presented in the paper aims to establish in labora-tory conditions, using the similitude criteria, the real value and the duration of a three phase short-circuit current act-ing in renewable sources connected to the electric grids. Since, due to the high values of the short-circuit currents it is difficult to test the operation of the relays in situ, for in-stance in transformer stations or substations, it is manda-tory to test and set using the injection of secondary currents. Consequently, the paper presents the modeling of a real grid, in order to emulate, as accurate as possible. The results of the measurements, reported to the real grid, represent the real ones, existing at the three phase short-circuit level. Therefore, even from the early phase of design, one may choose the breaking equipment, capable to face the condi-tions of dynamic and thermal stability. Since the reporting factors are known, along with the possibility of using the accurate reported value of the real short-circuit current on the model, the tests on model present advantages in relation to the use of the devices of secondary currents injection. The results of the measurements on the model confirm the vi-ability of the last testing method here depicted. images

Continuous Monitoring and SCADA Integration of the Sag of Overhead Electricity Transmission Cables Based on the Measurement of their Slope

Abstract

This paper presents a proposed system for the continuous monitoring of conductor sag values in overhead electricity transmission lines through slope angle measure-ment, by using a mathematical model based on the catenary equation. By measuring the axial angle of the conductor and the slope angle by means of the double axis tilt sensor, the sag value can be calculated in case of cable swings. Using ModBus protocol the value of the tilt sensor can be read by the software application and the calculed sag value is send to SCADA. The results obtained according to the proposed algorithm developed in LabVIEW software environment showed that the system could meet the technical require-ments for measuring conductor sag in electricity transmis-sion lines. images