To reduce the touch voltage at power plants and substations use the laying of a surface layer with a resistivity greater than the original soil. Determining the ground resistance of human foot (resistance of the surface of such a layer) is an important characteristic that must be taken into account both when designing a grounding device and during operation. Despite the practical measurement of the specified value by the specialists of Institute “Molniya” of the NTU “KhPI”, the issue of determining the resistance of the base is not covered in scientific and scientific-practical publications of Ukraine. Therefore, one of the goals of the authors is to draw attention and raise a dispute regarding the methods for determining this parameter. The first step towards this was the review and analysis of existing methods of determination. The experimental and computational methods for determining the ground resistance of human feet and recommendations for their use are were analyzed. The analysis of all known methods for determining the resistance of base made it possible to group ones into groups of calculation and experimental methods (the total number of analyzed methods is 21). Based on the results of the analysis of a number of literature sources and practical experience of monitoring the condition of grounding system, the advantages and disadvantages of each method are determined. Recommendations for their use depending on the condition of the object (current or designed), weather conditions, the presence of additional local inclusions or service areas. The practical significance of the work is the ability to optimally choose the method of determining the resistance of the surface during the control of the state of the grounding device The analysis determines the limits of the use of specific engineering techniques and is useful for designers and highly qualified specialists who perform work on diagnosing grounding devices of existing power facilities.
For test operations according to the liquid dielectric breakdown voltage measurement method we use high voltage machines that consist of high-voltage step-up transformer, voltage rise block, test cell with electrodes and so on. Described dielectric oil's test machine UIM – 90 with electromechanical voltage rise block. Cause of hard requirements in specification documents about voltage sine wave form on cell's electrodes, we performed field tests for UIM – 90 that help to evaluate the mains voltage impact on the test voltage distortion and measurement accuracy. Was discovered that during usage of electromechanical voltage rise block voltage steps disrupt sine wave’s form proportionally to step-up transformer’s transformation coefficient. Performed analysis of this block’s construction and established that usage of ЛАТР and mechanical voltage controller could lead to additional sine’s wave disruption. Decided to develop electronic voltage rise block which will allow to get rid of mains influence on test data. Created the algorithm of wave shaping from microcontroller, which generates voltage ramp to the amplifier representing pulse width modulator, then to the step-up transformers cascade. Proposed to use additional transformer for level matching of amplifier’s output voltage and main high voltage transformer’s input voltage. Presented flow sheet for UIM – 90 with electronic voltage step-up block and cascading start ofstep-up transformers. Provided voltage oscillograph trace and it spectrograph on the main transformer’s primary side, received due to the implementation of developed electronic voltage step-up block, prove that voltage sine wave form doesn’t rely on mains quality. After upgraded UIM – 90 and it world analogues technical parameters analysis we could make a conclusion about it competitive capability on global level.
Ensuring the permissible value of the touch voltage in operating electrical installations is a necessary condition for the electrical safety of personnel and third parties. In the study, based on literature data, it is analyzed in which cases it is impossible to achieve the permissible values of the touch voltage only with the help of the design of the grounding system. It is shown that ensuring the permissible value of the touch voltage is performed by arranging in a special way both the place of operational maintenance of the equipment and the territory of the opendoor switchgear. It is study the selection a technique of arrangement of the service place to ensure the permissible value of the touch voltage on the equipment of the opendoor switchgear during a single-phase short circuit to the ground. When performing the work, statistical methods of analysis, the ammeter-voltmeter method for experimental determination of the resistance of the base according to the method of Research&Design institute "Molniya" NTU "KhPI" were used. For the first time, on the basis of statistical data, the necessity of arrangement of equipment service area to ensure an acceptable value of touch voltage at operating substations of class 110 (150) kV and 330 (220) kV was analyzed. The spread of base resistance (ground resistance of human foot) values was determined experimentally. The most common ways of arrangement of equipment service area were analyzed: technological (natural), namely: a reinforced concrete pool with a layer of crushed stone, a cable channel or tray, asphalt paths and specially created (artificial) ones, namely: a metal structure , a layer of crushed stone, reinforced concrete slabs, concrete slabs without scaffolding, paving slabs, concrete slabs (paving slabs) with gravel admixtures, polymer sand slabs. The base resistance was measured for the listed techniques at operating substations. The advantages and disadvantages of various arrangement of equipment service area are determined, and recommendations for their use are provided.
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