Category Archives: Fără categorie

Use of Modern Computing Technique to Improve the Energy Indicators of Drive Motors of the Coal Mills

17 December 2015Fără categoriecburada

Abstract

In this paper, the authors present a study on the energetic opportunity to replace derated motors of the five mills which are in service at a power plant with other motors by a rated power closer to the actual load. To this end, it has previously been drawn up a suggestive comparative analysis of diagrams of active and reactive power balance in absolute and percentage values for each case of considered constructive variants. Thus for drawing up, using the complete mathematical model (BEMAS) chosen for the asynchronous machine, of the electric balances for different operating regimes of these asynchronous motors, it was necessary to determine the parameters of the equivalent diagram. Considering the complexity and large volume of computation, the authors developed for this purpose, specific computational algorithms. For all these computational algorithms, computation programs have been drawn, being developed in the programming environment Mathcad Version 7.0, of own conception and which in principle can be used for any other similar motors that have different nominal data. It has also been highlighted that the starting point to establishing the opportunity of replacing of the analyzed asynchronous motors operating derated in steady state, is determining the actual load degree that is achieved through active power measurement for the considered regime.

Virtual Synchronoscope for Connecting Synchronous Generator on the Grid

17 December 2015Fără categoriecburada

Abstract

In this paper is presented in a constructive and functional way an instrument that can be used at connecting synchronous generators at the grid supply that has a constant voltage and frequency. Actually it is about a virtual synchronoscope that verifies the correct instant for the synchronization: phase sequence of the generator must be same with the grid, the generator frequency must be equal to the grid frequency, the generator voltages should be equal to the corresponding grid voltages and the generator voltages should be in phase with the corresponding grid voltages. After the conditions of synchronization between synchronous generator and large power grid are occur, the parallel operation of generator is realized automatically. The virtual synchronoscope is designed from two principal components: hardware (LEMs transducer for measurement six voltages, supply voltage, elements for input/output signals conditioning, USB multifunction I/O module) and software (virtual instrument). The main objective of this paper is to create aneasy to use device for the study of network synchronization synchronous generators. The LabVIEW graphical programming environment is used for designing virtual instrument. The monitored parameters values are displayed using digital indicators. The real-time voltage waveforms for grid and generator are displayed. With three-phase voltage phasors (voltage vectors) we can see the evolution of phase angles and voltages amplitude. This virtual synchronoscope can be used in engineering education from universities or intesting laboratories of electrical machines.

Increasing Safety of the Tests Carried Out in Laboratories by Using Electronic Devices

17 December 2015Fără categoriecburada

Abstract

The ability of the circuit breakers to interrupt the electrical current in circuits with capacitive load it is tested and verified in testing laboratories. During the test, the capacitive type of load impedance simulates an overhead line or an underground cable that works with no load impedance. The transient behaviour which appears at the opening of electric circuits having capacitive load impedance can determine the appearance of some dangerous over-voltages for line, cables and equipments. After testing, at the circuit interruption, it is possible to be residual electrical charge on capacitors. This endangers the lives of people who configures the test scheme. The paper describes a device that monitors the voltage on the capacitors that are connected to busbars and which alerts the staff about the presence of electric charges remaining at the end of the test. A referral unit is mounted near the bars to that are connected capacitors, while warning unit is mounted in the place where can be observed by personnel that configure the test schemes. Two variants of the device are presented. The results, obtained with the device during carrying out tests, both in the laboratory and in operation, are presented into the final section of the paper.

Energetic Influence of Motor Power in Drive Systems with Space-Vector Static Converters and Induction Motors

17 December 2015Fără categoriecburada

Abstract

–The static converters are a vital component of modern drive systems, which in turn are indispensable in industrial equipment designed for small or large complexity, because the achievement of finished goods implies the adjustable mechanical energy available at the output of the system. The aim of this paper is the energetic analysis of two drive systems with the same static converter feeding two different motors which had been performed on an experimental stand for different static operating points. It was considered feeding the both asynchronous motors from the static converter using the space vector modulation command strategy while the mechanical load was assured by a special braking machine and by a DC motor, respectively. It had been taken into consideration feeding the both motors at the same frequencies and with the same RMS voltages. The frequencies considered for the energetic analysis are 20Hz, 30Hz, 40Hz and 50Hz, the mechanical load being adjusted from no load operation up to the nominal value. The power grid energetic parameters were recorded using a Fluke 41b harmonic analyzer, while the current and voltage waveforms at the motor input, were recorded using a Metrix Ox704 digital oscilloscope and later used in Matlab to calculate the AC electric powers.

Study of Indirect Current Control Methods for Urban Traction Active DC Substations

17 December 2015Fără categoriecburada

Abstract

Although the high power DC traction substations are using 12 pulse rectifier which have lower distortion than the classical 6 pulse rectifier, considering the high power, the reactive and harmonic components of the absorbed current are harmful to the power grid. The addition of an active compensator to the classical dc traction substation creates the “active substation”. The active substation allows bidirectional power flow between the power grid and the DC catenary, which means the active power flow from the power grid to the DC catenary and the recovered power flow from the catenary back to the power grid. At the same time, because the compensator acts like an active filter in the first case and like a power inverter in the last case, both the consumed and recovered power are active powers. To achieve this goal the active compensator must inject current to the point of common coupling, and the typical currentcontroller is the hysteresis regulator. At the same time, the typical approach on the injected current regulation is the direct current control, which implies the closed loop controlof the current at the compensator output, i.e. the current through the output inductors. A new approach is the closed loop control of the current absorbed from the power grid, i.e. the indirect control, for which the compensator controls the grid current, and for a given load current, the compensator injected current results from the first two.

Information and Communication Technology in Urban Electric Transportation

17 December 2015Fără categoriecburada

Abstract

This paper is a first attempt at assessing the impact of information and communication technology in transport, with an accent on electric public transportation. Information and communication technology is present in all spheres of human activity. Transport systems are made of vehicles and infrastructure. Modern vehicles are filled with complex technology, such as electric drives, mechatronics, artificialintelligence and information and communication technology. And the infrastructure currently numbers only the roads and traffic lights, but the evolution of things leads to Intelligent Transport System. A technology that would connect vehicles and infrastructure to make transportation on land safer and more efficient. Electric vehicles require special attention to motor control. Power converters driven by intelligent modules allow an efficient control of the motor. A series of electronic systems for trolleybus and tram control, the SDMC, were made in Chiinău by the Informbusiness Company. The SDMC systems are intelligent system, built on microprocessors and CAN communication protocol. Modern ICT technology allows simultaneously to ensures diagnostics, monitoring and protection of all components; to store the current state of the elements; to provide information means for the driver and passengers and ensure good function of complex control algorithms. Information technology is present also in intelligent transportation systems with smart or even driverless vehicles. Technologies such as GPS and Wireless Networking allow optimizing urban transport, and are basic stones in the future of transport, which includes Intelligent Transport Systems and Driverless vehicles.

Transversal Shape Optimization of a Brushless DC Motor for Electric Vehicles

17 December 2015Fără categoriecburada

Abstract

The opportunity of this research is to emphasize certain approaches related to the design and modeling of low and medium power permanent magnet brushless DC motors for electric vehicles, which are presently poorly treated. The challenge of any manufacturer is to develop electric machines with minimum manufacture and maintenance costs by accomplishing the performance required by the customer. One looks for mathematical models as exact as possible as tools for the design and parameter computation. As a consequence of the progress of control and power electronics, the performances of brushless DC motors have been improved. Therefore, the problems of optimal design and optimal operating mode of such motors are currently reported by the technical literature. By exploiting the available numerical computation tools, we developed the optimized technical design of a brushless DC motor for an electric bicycle. The performed simulations emphasize the technical performances which accomplish the customer requirements as follows: manufacture cost reduction of 27.9%, total cost reduction of 9.11% and a slightly growth of the maintenance cost of 8.01%. It is advisable to do a periodical optimal re-design, which will take into account new performant electrotechnical materials with adequate technologies, in order to decrease the fabrication cost and to increase the energy efficiency of brushless direct current motors. The optimized motor achieves the required overallsize.

Factors Involved in Choosing LEDs for General Lighting Applications: a Critical Review

17 December 2015Fără categoriecburada

Abstract 

 

Electric lighting accounts for 19% of electricity consumption worldwide and generates remarkable concern to get energy savings. As a modern source of light, LEDs open up a multitude of innovative lighting solutions. LEDs lighting is already widely used in many niche areas like traffic lights, car lights, lighting displays, TVs etc. Now, based on lowered manufacturing costs, they penetrate into the general lighting market. But for specialists, LEDs are not yet the end solution in any lighting application. There are a lot of factors that can influence their adoption decision.Among them, the most favorable and promising one is the high efficiency, with values in permanent increasing. The paper discusses various aspects of LEDs efficiency and demonstrates that luminous efficiency is not a relevant criteria for a decision, a better understanding being got with an indicator like the Lighting Power Density, in W/m2. And beyond the efficiency, the paper makes a critical analysis of other parameters that matters in the lighting decisionmaking process, like lifetime, color rendering and chromatic shift, health and environmental impact. Finally, the paper point out that the calculation of cost and return of investment represent a very technical effort, based on accuracy of the entry data, often unknown by the investor itself, like different confidential costs, daily average time of functioning, temperature hazards and lifetime in condition of poor quality of electricity.

Management of Renewable Energy Sources Integrated in a Micro Smart Grid

16 December 2015Fără categoriecburada

Abstract 

 

Future trends in the energy sector are crossing from centralized to distributed electricity production. A national and international organism encourages and informs consumers about the efficient use of energy. Such an approach of an efficient energy consumption lead to use of a certain number of renewable energy sources and a proper management of their. This paper, approach some issues of energy management and the use of unconventional sources of energy under the stochastic conditions. It showed a possibility of interconnection of renewable energy sources in a micro-smart grid. Four energy sources are proposed: the main source – power grid; secondary source 1 – photovoltaic generator; secondary source 2 – wind generator; secondary source backup 3 – diesel generator. The interconnection of these energy sources is achieved by a system of energy management and control based on a microcontroller structure type. Interconnection is based on the availability of energy sources and by energy consumption. The command and control algorithms for energy sources were implemented in Matlab Simulink software using specific functions and blocks. The energy management system ensures directing the flow of energy between sources and consumers. Also it manages the total energy distributed to consumers. The information can be stored and interpreted by a PC.

Lead Acid Battery Pack Charging Optimization

16 December 2015Fără categoriecburada

Abstract 

Still used as a rechargeable power sources, rechargeable batteries pack require attention primarily to ensure higher life operating. One of the factors that influence lifespan is the process of charging and discharging. For batteries is manifested in the so-called memory effect which manifests itself by decreasing the operating voltage, even when was loaded to its maximum capacity. The article presents this issue but also offers a solution direct applicable for lead-acid batteries. The principle has based on reducing the number of charge and discharge processes in a certain time. So the hysteresis characteristic becomes wider and the time between switching from charge mode in the discharge and vice versa is higher. Analysis of three algorithms, step-by-step set of operations, and implementation in an experimental device is the main goals of paper. Optimization technique represents here to maximize battery lifetime. The device developed has a microcontroller and proves useful with minimal changes in any situation, by replacing the existing or interposing circuit between the power source and battery. Designed circuit can have easily adapted to correspond for other types of batteries. It can integrate with minimal changes, additional functions such as current battery measure and temperature.