POMIAR WSPÓŁCZYNNIKA PRZEWODNOŚCI CIEPLNEJ WŁAŚCIWEJ CIECZY ELEKTROIZOLACYJNYCH Z WYKORZYSTANIEM AUTORSKIEGO UKŁADU POMIAROWEGO

The paper presents the results of measurements of the thermal conductivity coefficient of the selected insulating liquids according to the temperature. The value of the thermal coefficient of tested insulating liquids at temperatures from 20°C to 100°C was determined. Measurement of thermal conductivity was conducted by the use of presented authoring measurement system. The obtained results are essential to the design of power devices structures.W artykule przedstawione zostały wyniki pomiarów współczynnika przewodności cieplnej właściwej wybranych cieczy elektroizolacyjnych w zależności od temperatury. Określona została wartość współczynnika przewodności cieplnej badanych cieczy elektroizolacyjnych w przedziale temperatury od 20°C do 100°C. Pomiar przewodności cieplnej przeprowadzono przy wykorzystaniu przedstawionego autorskiego układu pomiarowego. Uzyskane wyniki są istotne z punktu widzenia projektowania konstrukcji urządzeń elektroenergetycznych

Electro-Insulating Nanofluids Based on Synthetic Ester and TiO2 or C60 Nanoparticles in Power Transformer

The article discusses thermal properties of synthetic ester admixed with nanoparticles. The analyzed thermal properties were: thermal conductivity λ, kinematic viscosity υ, density ρ, specific heat cp, and the thermal expansion factor β- all obtained by means of measurements. On the basis of these, the authors calculated the heat transfer factor α, which determines the ability of the liquid to heat transport. The authors used nanoparticles of fullerene C60 and titanium oxide TiO2. The analysis of the thermal properties was done for the temperatures of 25, 40, 60 and 80 °C. The authors analyzed the impact of nanoparticles C60 and TiO2 on thermal properties of synthetic ester. They proved that fullerene C60 in principle had no influence on heat transfer factor α of the ester, while titanium oxide TiO2 had some positive influence on the factor, the value of which increased about 1–3%

Thermal properties of mixtures of mineral oil and natural ester in terms of their application in the transformer

The article describes research results of thermal properties of mineral oil and natural ester. Percentage proportions of both the liquids were as follows: 100/0, 95/5, 80/20, 50/50, 20/80, 0/100. The authors present measurement results of thermal conductivity, viscosity, specific heat, density, and thermal expansion of the created mixtures. The measurements were taken in a relatively wide temperature range: 25 °C, 40 °C, 60 °C, and 80 °C. On the basis of the measurement results, convection heat transfer coefficient α was calculated and the most advantageous proportion of both the components of the mixture was pointed in terms of cooling effectiveness of the transformer

Lack of Thermogram Sharpness as Component of Thermographic Temperature Measurement Uncertainty Budget

The number of components of a thermographic temperature measurement uncertainty budget and their ultimate contribution depend on the conditions in which the measurement is performed. The acquired data determine the accuracy with which the uncertainty component is estimated. Unfortunately, when some factors have to be taken into account, it is difficult to determine the value of the uncertainty component caused by the occurrence of this factor. In the case of a thermographic temperature measurement, such a factor is the lack of sharpness of the registered thermogram. This problem intensifies when an additional macro lens must be used. Therefore, it is decided to commence research to prepare an uncertainty budget of thermographic measurement with an additional macro lens based on the B method described in EA-4/02 (European Accreditation publications). As a result, the contribution of factors in the uncertainty budget of thermographic measurement with additional macro lens and the value of expanded uncertainty were obtained

The Solution for the Thermographic Measurement of the Temperature of a Small Object

This article describes the measuring system and the influence of selected factors on the accuracy of thermographic temperature measurement using a macrolens. This method enables thermographic measurement of the temperature of a small object with an area of square millimeters as, e.g., electronic elements. Damage to electronic components is often preceded by a rise in temperature, and an effective way to diagnose such components is the use of a thermographic camera. The ability to diagnose a device under full load makes thermography a very practical method that allows us to assess the condition of the device during operation. The accuracy of such a measurement depends on the conditions in which it is carried out. The incorrect selection of at least one parameter compensating the influence of the factor occurring during the measurement may cause the indicated value to differ from the correct value. This paper presents the basic issues linked to thermographic measurements and highlights the sources of errors. A measuring stand which enables the assessment of the influence of selected factors on the accuracy of thermographic measurement of electronic elements with the use of a macrolens is presented

Comparison of mineral oil and esters as cooling liquids in high voltage transformer in aspect of environment protection

The article presents the results of computer simulation of temperature field of transformer filled with mineral oil and alternatives insulating liquids which include synthetic and natural esters. The analysis was based on the results of computer simulation of temperature field of 10 MVA distribution transformer, using the program COMSOL Multiphysics

The Possibilities to Reduce Arc Flash Exposure with Arc Fault Eliminators

This paper presents a method to limit the arc energy and hence the hazard risk category value according to IEEE 1584 by using a system of two oppositely connected multi-sectional thyristor branches. A test circuit for testing the effectiveness of a thyristor arc eliminator was designed and constructed. Arc ignition inside electrical switchgear can be a source of danger for technical personnel. The arc energy calculated according to the algorithms in IEEE 1584 can be significantly reduced by using multi-sectional arc eliminator MSAE. For the actual measuring object, the calculation of the hazardous arc flash zone and the hazard category was carried out for the system not equipped with an arc eliminator, and then the same was performed in a system with an arc eliminator. In parallel, the pressure inside the closed polyvinyl chloride (PVC) electrical box enclosure was measured and then compared with the calculated pressures that could occur during an arc fault. It was found that a Multi-Sectional Arc Eliminator (MSAE) effectively protects devices supplied from low voltage networks against the effects of short circuit or arc fault, such as the sudden increase of gas pressure inside the switchboard, which may cause it to break, significantly reduce the loss of electrode material, limit the spread of hot electrode material outside the switchgear, and also significantly reduces the energy of the electric arc

Change in Electric Contact Resistance of Low-Voltage Relays Affected by Fault Current

Contact resistance is an important maintenance parameter for electromagnetic switches, including low-voltage relays. The flow of significant current through electric contacts may influence the contact surface and thus the value of the electric contact resistance (ECR). The change in ECR is influenced not only by the value of current but also by the current phase. Therefore, the impact of the switching short-circuit current’s phase on the ECR was analyzed in this paper. Significant changes in the resistance after each switching cycle were observed. The ECR decreased significantly after each make operation, and a correlation with current amplitude, total let-through energy, and short-circuit time was not observed