Investigation of Thermal Stability of 0.6/1 kV Metal-Coated Carbon Fiber Cable and Joint

For this paper, we manufactured the 0.6/1 kV 3-core cable using metal-coated carbon fiber (MCF), which can be utilized for a cable screen layer. This cable can be applied to non-earthed system, and has a shielding property of more than 90% of braiding density. However, new joints and methods are needed to connect the cables because carbon fiber has brittleness. Thus, the cable connection added a spring to the contact surface, reducing resistance and fiber brittleness. These cables and connection methods were evaluated for safety in a certain temperature, humidity and over-current environments. From the results, the change of the external shape and contact resistance of the cable and the joint against the humidity and temperature were not significant, and the insulation breakdown did not occur in the withstanding voltage property of 3.5 kV for 5 min. No thermal deformation of the cable and connections was observed at the current above the allowable current range; it can be used as stable as metal screen cable.

Mathematical model of insulation breakdown prediction based on partial discharge characteristics

The paper investigates the existing mathematical models of insulation destruction. It has been determined that most of the models for assessing the residual life of insulation are based on models of thermal and thermo-oxidative destruction of insulation materials. Currently, solid dielectrics are gaining popularity, including crosslinked polyethylene, PVC, ethylene-propylene rubber, and others. In such dielectrics, it is possible to estimate the residual life in the short term. This possibility and necessity is due to the possibility of growth of tree defects under the influence of partial discharges. The article describes the proposed mathematical model for assessing the residual resource of insulation by modeling the growth of a defect. To take into account the influence of random variables, the model uses the Weibull distribution. The model assumes the division of the insulation thickness into some areas, each of which is destroyed independently of the others. The destruction of these areas occurs when partial discharges occur with certain energy sufficient to destroy the material. Insulation failure is predicted using the least squares method. The results obtained can be useful in assessing the residual life of insulating materials and in conducting research in this area

Analysis of the causes of traction electric failures of electric cargo cars operated on railways of the Republic of Uzbekistan

In this article, it is considered to analyze the reliability of TEM (traction electric machine) of electric locomotives of the railways of the Republic of Uzbekistan. To determine the damage, the most expedient and effective method will be to extend the life of the insulation by encapsulating local damage using impregnating materials and heat radiation. Over the past ten years, a stable tendency for insulation breakdown and turn-to-turn closure of the armature winding of the NB-514 type has been maintained in Unitary Enterprise (UE) “O'ztemiryo'lmashta'mir.” In this regard, a hypothesis was put forward that insulation breakdowns and turn-to-turn short-circuit of the armature winding most often occur due to intense heat and mass exchange processes in the insulation of the frontal parts of their windings with open section heads.

Experimental investigation of insulation resistance for turbo generator digital protection

Insulation of all electrical machinery is practically in the form of organic compounds that contain water as part of their make-up. Excessive temperature tends to dehydrate and oxidize the insulation and make it become brittle and disintegrate under vibration and shock. The insulation lifespan of turbo generators deteriorates slowly at low temperatures and more rapidly at high temperature. Economic factors, such as initial cost, replacement cost, obsolescence, and maintenance, are of prime importance when determining the years of useful service desired for the electrical insulation. Generator digital protection- fault diagnosis test was carried out to find out the cause of insulation breakdown on the turbo generator unit 411G3. The experimental procedure consists of an insulation resistance test, meggering (time-resistance absorption test), and pendulum over-speed test. A thorough investigation was conducted to identify all the stator bars that constituted the Red phase and other connections. Voltage drops on these stator bars were measured and values were used to detect ground faults which were rectified via an intelligent protection scheme.

Improved Insulation Durability to Improve Transformer Aging

In transformers, in addition to the primary and secondary coils, there are several other important components and accessories in which the insulating material is one of the most critical components of a transformer. Sufficient insulation between different active parts are necessary for safe operation. Adequate insulation, it is not only necessary to insulate the coils from each other, or from the core and tank, but also guarantees the safety of the transformer against accidental surges, but with the growth in size and complexity of power stations, transformer is facing insulation problems. The evaluation of the transformer overload capacities certainly leads to complex variables that affect the operating life of the power and distribution transformer. In this study, the long-life calculation is performed on the basis of two experiments, which are related to the insulation degradation of the mineral oil and cellulose paper such as by adding different types of nano-particles to the mineral oil to enhance the strength of oil, and by changing the loads under different operating conditions to control the deteriorating rate of the insulation to prevent the life of the transformer. The insulation breakdown strength is improved from 37 kV to 71 kV by mixing the semiconductor nanoparticles such as gadolinium-doped ceria (GDC) and cerium dioxide (CeO2) with mineral oil. Moreover, for cellulose paper, thermal degradation rate is kept below its limit by reducing the temperature when controlling the load.

Improving the reliability of power supply to active consumers by improving the technology for manufacturing cable product

The growing demand for high-quality transmission of electrical energy with a high level of reliability of cable lines is determined not only by the conditions of operation, installation, but also by the technology of cable production. This article discusses the issues of increasing the reliability of power supply to active consumers, which is achieved through the use of cable products with a higher level of reliability. The concept of "reliability", disclosed in the article, is valid for all cables and wires with insulation, which must maintain integrity as part of the product for the entire period of operation. The use of fundamentally improved technological processes, as the conducted study shows, makes it possible to reduce ohmic resistance of the conductive part of the cable product and thereby allows reducing the temperature parameters of the operating cable line. Cable failure, in most cases, is associated with insulation breakdown, the reason for which can be caused by a rise in temperature inside the cable insulation. In this regard, the creation of conditions for reducing the ohmic resistance of a current-carrying conductor is one of the ways to increase the reliability of a cable product at the stage of its manufacture. Proposed technical solution, considered in this article, is focused on the technological operation - drawing, where changes in the standard drawing route make possible reduction of the ohmic resistance of the current-carrying conductor by 3-5% for copper and aluminum, respectively.