Considerations regarding the choice of cable glands for electrical equipment used in potentially explosive atmospheres

The evaluation of explosion-proof electrical equipment for certification is particularly important given the risk of explosion and must be minimized. This in order to ensure the safety of life, health of workers, to prevent damage to goods and the environment when they meet the essential security requirements at European level. Directive 2014/34 / EU states that equipment used in explosive atmospheres must be designed to operate without endangering the environment for which it is intended. This paper presents a comparison between the different types of cable glands for electrical apparatus by comparing some common characteristics that are important for maintaining the integrity of explosion protection. Consequently, this paper intends to be the precursor of a practical guide for the selection and implementation of different types of protection on the apparatus intended for use in areas with hazard of explosive atmospheres, both for designers and manufactures. This state of fact is negatively more emphatic because, lately, the groups of standards from this field in the world, Europe and Romania have a peculiar dynamic caused especially by the homogenisation and generalisation process opened and maintained by IEC.

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.

Lesand E. Hinsie (Wien. K]., No. 22, 1931)

(Wien. K]., No. 22, 1931). An article by an American author on radiothermal treatment, progress. paralysis translated into German for Wien. kl. Woch. Wagner-Jauregg. Hinsie places the paralytic in a heat-producing electrical apparatus called a radiotherm. In this apparatus, the paralytic lies in an electric alternating field (Wechselfeld) of 3000 volts potential difference

Advanced method for determining the steady temperature and constant heating time of electric apparatus

The article proposes an improvement in the method for determining the steady-state heating temperature of current-carrying parts of an electrical apparatus and its time constant in the case of real measurements of temperature values made with some error. In accordance with the specified method, at a known ambient temperature, the apparatus is turned on with the measurement of its heating temperature at regular intervals; based on the measurement data, a graph of the temperature derivative is plotted over time; according to the data of the graph, the steady-state temperature and the constant heating time are determined. It is shown that inaccuracies in temperature measurement can significantly distort the dependences obtained for determining the time constant and the steady-state heating temperature, and for a correct estimation of the parameters, the form of the approximating function of the temperature derivative with respect to time must be known a priori - a linear function. This method can significantly reduce the time for testing electrical devices for heating in continuous operation. This method is illustrated by the example of determining the heating of the coil over time by measuring the active resistance. On the basis of the obtained and processed experimental data, the power overload coefficients are also determined in the long-term operation mode, as well as in the short-term and intermittent modes, which makes it possible to correctly operate the electrical apparatus.

Mechanical Calculation of Flexible Wires Taking into Account Taps to Electrical Apparatuses

A method is proposed for the mechanical calculation of flexible wires of substation in the presence of one tap to an electrical apparatus located in the middle of the span, taking into account its real location. The technique takes into account the presence of tension insulators strings, different heights of the suspension of wires. The loads on the conductor and tap depend on the climatic regime and take into account wind and icy conditions, as well as temperature changes. The transition to another climatic regime is performed by solving the equation of state, taking into account the coefficients of the horizontal and vertical load of the given and initial regimes. Formulas are given for calculating load factors that take into account weight, wind and ice cover loads on wires and insulator strings, as well as the slope of the span. They are calculated for each climatic mode based on the actual location of the tap to the electrical apparatus and the forces from it to the busbar. It is shown that the calculation results are in good agreement with the proposed method and the computer program. Formulas are given for calculating the sag and horizontal deviations of the wires when the tap is located in the middle of the span. A method is proposed for calculating the components of the forces on the busbar from the tap, taking into account its real location in substation. Formulas for calculating these components are given for different variants of the tap orientation. Knowledge of the values of the components of concentrated forces from the tap allows to increase the accuracy of calculating the sag and tension of the substation wires. Formulas are given for calculating the coefficients of increasing the sag, taking into account the components of the forces from the tap.

THE DIGITALIZATION OF SUBSTATIONS BY CREATING A 6-35 kV SWITCHING DEVICESCONTROL SYSTEM FROM THE AUTOMATED WORKPLACE

The control system of high-voltage switches at one of the substations of the branch of JSC «Grid Company» Buinskie Power Networks is presented in the work. The block control circuit of switching devices from the automated workplace is described. Its specific blocks with the help of which the whole process of switching of high-voltage switches in the switchgear – 10, 35 kV is performed are provided. An explanation of the collection and transfer of information from intelligent electronic devices to the switchgear drive, transmission of control commands, protocol conversion and data exchange with higher levels of automated systems is given. Advantages of the remote control system for 6-35 kV electrical apparatus are shown on the example of the 110/35/10 kV «Verkhny Uslon» substation of the Tatenergo system. The system of remote control of switchgear during its repair and in case of other emergency situations is opened on the example of one of the substations 110/35/10 kV of the Republic of Tatarstan. There are schemes KRUN-10, KRUN-35 kV with an illustration of the positions of electrical apparatus, combined with video surveillance of the state of the switch of a certain cell and the position of the earthing switch of a separate switching device.

Investigation of Survival/Hazard Rate of Natural Ester Treated with Al2O3 Nanoparticle for Power Transformer Liquid Dielectric

Increasing usage of petroleum-based insulating oils in electrical apparatus has led to increase in pollution and, at the same time, the oils adversely affect the life of electrical apparatus. This increases the demand of Mineral Oil (MO), which is on the verge of extinction and leads to conducting tests on natural esters. This work discusses dielectric endurance of Marula Oil (MRO), a natural ester modified using Conductive Nano Particle (CNP) to replace petroleum-based dielectric oils for power transformer applications. The Al2O3 is a CNP that has a melting point of 2072 °C and a low charge relaxation time that allows time to quench free electrons during electrical discharge. Al2O3 is blended with the MRO and Mineral Oil (MO) in different concentrations. The measured dielectric properties are transformed into mathematical equations using the Lagrange interpolation polynomial functions and compared with the predicted values either using Gaussian or Fourier distribution functions. Addition of Al2O3 indicates that 0.75 g/L in MRO has an 80% survival rate and 20% hazard rate compared to MO which has 50% survival rate and 50% hazard rate. Considering the measured or interpolated values and the predicted values, they are used to identify the MRO and MO’s optimum concentration produces better results. The test result confirms the enhancement of the breakdown voltage up to 64%, kinematic viscosity is lowered by up to 40% at 110 °C, and flash/fire points of MRO after Al2O3 treatment enhanced to 14% and 23%. Hence the endurance of Al2O3 in MRO proves to be effective against electrical, physical and thermal stress.

Diagnostic Simplexes for Dissolved-Gas Analysis

A Duval triangle is a diagram used for fault type identification in dissolved-gas analysis of oil-filled high-voltage transformers and other electrical apparatus. The proportional concentrations of three fault gases (such as methane, ethylene, and acetylene) are used as coordinates to plot a point in an equilateral triangle and identify the fault zone in which it is located. Each point in the triangle corresponds to a unique combination of gas proportions. Diagnostic pentagons published by Duval and others seek to emulate the triangles while incorporating five fault gases instead of three. Unfortunately the mapping of five gas proportions to a point inside a two-dimensional pentagon is many-to-one; consequently, dissimilar combinations of gas proportions are mapped to the same point in the pentagon, resulting in mis-diagnosis. One solution is to replace the pentagon with a four-dimensional simplex, a direct generalization of the Duval triangle. In a comparison using cases confirmed by inspection, the simplex outperformed three ratio methods, Duval triangle 1, and two pentagons.