Resistance change of contact groups of low-voltage electrical apparatus: Determining the laws

The main Russian and foreign manufacturers of low-voltage electrical devices - circuit breakers, fuses, magnetic starters, knife switches and packet switches are presented. The data of experiments for determining the resistance values of contact groups of low-voltage switching equipment are considered. The design features of the devices that determine the value of the resistances of the power circuits of low-voltage equipment are investigated and a classification is proposed depending on the design elements of the devices. A methodological approach and an algorithm for experiments and detailed analysis of the contact groups of devices are given. Experimental schemes for the study of contact groups are proposed. The data of the conducted experiments on the study of contact groups and the resistance values as a function of the flowing currents are shown. During the experiments it is revealed that the value of the resistance of the contacts changes depending on the value, type and time of exposure to current within +/-5 %. The laws that characterize the ratio of the resistance values of the structural components of devices (contact systems, thermal relay, coil of the maximum relay) have been revealed and defined. Empirical expressions and graphical dependences of the resistances of contacts and contact systems are obtained as a function of the magnitude of the rated currents of low-voltage contact equipment. The minimum sample size of the number of devices during experimental research is determined, sufficient to calculate the mathematical expectation of the resistances of the contact connections of the devices with a given accuracy. As a result of experimental studies, it is revealed that the resistance value of contacts and contact joints can increase during operation by 2-2.5 times. The established dependences of the change in contact resistance can be used to predict the technical state of electrical installations of intrashop low-voltage networks, to clarify the amount of electricity losses in shop networks up to 1 kV, and can also be used as an additional regulation for maintenance and scheduled preventive maintenance.

Simulación mediante CDF de una chimenea solar inclinada sobre la cubierta

In recent years, energy consumption from electrical devices to foster air movement in regions with warm climates has risen, with the resulting negative impact on the environment. The purpose of this paper is to evaluate the performance of a solar chimney used to induce natural ventilation in a closed space, under the weather conditions of the hot humid Mexican climate. For this purpose, CFD simulations were run using the RNG k- ɛ turbulence model and the DO radiation model, considering only natural convection phenomena. The solar chimney performance was evaluated, comparing the results of the simulations with experimental measurements, analysis which showed a good match. Temperatures of up to 46.5%°C in the air within the chimney, and of 77.1°C on the absorption plate, were obtained, results that allow verifying the influence of the heat discharge phenomenon by the natural flotation of air in the chimney.

THERMAL ANALYSIS OF HIGH-CURRENT ELECTRIC CONTACT

This paper deals with mathematical modelling of the temperature distribution in the vicinity of a direct electrical high-current contact under the action of a nominal current of 3000 A. High-current electrical contacts belong among the elements by which a large number of electrical devices are connected. They play an important role especially in the transmission and distribution system, where they have to withstand adverse weather conditions that have a significant impact on their degradation.

Analysis methodology for the design of start-up rheostats on thermo-dependent polycrystalline resistances

The article provides a brief analysis of the starting processes of electrical devices in autonomous systems of limited power. The existing methods of automatic start-up and regulation of the operation of electrical machines and apparatus are considered, which are a multi-link system, the reliability of which is determined by a number of intermediate links, and the stepping is one of the biggest drawbacks that negatively affect the dynamics of the starting process. In addition, the issues of simplicity, low cost and small dimensions of the automatic control system for electrical installations are of particular importance in the problem of energy saving. The use of low-power thermistors as part of starting devices requires intermediate equipment and various components, which significantly reduces the reliability of the equipment. The increase in currents flowing through the ballasts simplifies the electrical control and regulation circuits. For the use of polycrystalline semiconductor thermistors in circuits with high currents, it is necessary to use special designs in order to prevent overheating of the thermistor material. The article provides algorithms for the synthesis of starting rheostats. A number of restrictions are considered and formulated, on which the nature of the processes of starting electric motors with the help of thermistor rheostats, which ensure the fulfillment of certain restrictions, depends. Recommendations are given for the formation of optimal starting processes using rheostats built on semiconductor polycrystalline thermistors.

Hexagonal Ferrites, Synthesis, Properties and Their Applications

We intend to report on possible fabrication routes for all types of hexagonal ferrites which are known for their wide area of use and applications. Hexagonal ferrites have now become an intense topic of research as they are the part of most of magnetic recording and data storage applications globally. Hexagonal or popularly known as ‘Heaxa-ferrites’ are known for their utilization in permanent magnets and their utilization in electrical devices being operated at high frequencies especially at GHz frequencies. We have presented in this chapter all main six types of hexagonal ferrites i.e. M Type, Z-Type, Y-type, W-type, X-Type and U-type hexa-ferrites. Hexaferrites belong to ferromagnetic class of magnetic materials and their properties are purely dependent on intrinsic structure of ferrites. In this chapter, we aim to discuss more on M-type of hexa-ferrites, their properties and their applications. Also, recent advances on M-type ferrites are also a part of this chapter.

A Highly Accurate NILM: With an Electro-Spectral Space That Best Fits Algorithm’s National Deployment Requirements

The central problems of some of the existing Non-Intrusive Load Monitoring (NILM) algorithms are indicated as: (1) higher required electrical device identification accuracy; (2) the fact that they enable training over a larger device count; and (3) their ability to be trained faster, limiting them from usage in industrial premises and external grids due to their sensitivity to various device types found in residential premises. The algorithm accuracy is higher compared to previous work and is capable of training over at least thirteen electrical devices collaboratively, a number that could be much higher if such a dataset is generated. The algorithm trains the data around 1.8×108 faster due to a higher sampling rate. These improvements potentially enable the algorithm to be suitable for future “grids and industrial premises load identification” systems. The algorithm builds on new principles: an electro-spectral features preprocessor, a faster waveform sampling sensor, a shorter required duration for the recorded data set, and the use of current waveforms vs. energy load profile, as was the case in previous NILM algorithms. Since the algorithm is intended for operation in any industrial premises or grid location, fast training is required. Known classification algorithms are comparatively trained using the proposed preprocessor over residential datasets, and in addition, the algorithm is compared to five known low-sampling NILM rate algorithms. The proposed spectral algorithm achieved 98% accuracy in terms of device identification over two international datasets, which is higher than the usual success of NILM algorithms.

MoTe2 Field-Effect Transistors with Low Contact Resistance through Phase Tuning by Laser Irradiation

Due to their extraordinary electrical and physical properties, two-dimensional (2D) transition metal dichalcogenides (TMDs) are considered promising for use in next-generation electrical devices. However, the application of TMD-based devices is limited because of the Schottky barrier interface resulting from the absence of dangling bonds on the TMDs’ surface. Here, we introduce a facile phase-tuning approach for forming a homogenous interface between semiconducting hexagonal (2H) and semi-metallic monoclinic (1T’) molybdenum ditelluride (MoTe2). The formation of ohmic contacts increases the charge carrier mobility of MoTe2 field-effect transistor devices to 16.1 cm2 V−1s−1 with high reproducibility, while maintaining a high on/off current ratio by efficiently improving charge injection at the interface. The proposed method enables a simple fabrication process, local patterning, and large-area scaling for the creation of high-performance 2D electronic devices.

Electrical Appliance Switching Controller by Brain Wave Spectrum Evaluation Using a Wireless EEG Headset

Disabled people are usually unable to interact with their surroundings efficiently, and performing tasks like switching an appliance on or off can be troublesome if the user is bedridden, for example. This article discusses an electrical appliance switching controller using a wireless EEG headset that is aimed to aid elderly people and the disabled. The system comprises of a MindLink EEG headset that is Bluetooth-connected to an Arduino microcontroller board. The system permits the user to separately switch on and off the 4 electrical devices connected to the power socket. The EEG signal is obtained to investigate the brain activity throughout the experiments done. Based on the brain wave signals read, attention and meditation are determined to be the most suitable for this project and is used to trigger the relay switching of the power socket. It is found that the response time to trigger the switching is slow as some users require practice or training to control their brain wave signals effectively. The work performed provides a rudimentary insight of a BCI system functionalities and presents a brainwave-controlled hardware switching for the bedridden or disabled patients.