Abstract
Target. High information value and reliability of diagnostics of isolation by partial discharges. Methods. Simulation of PD in Multisim and calculation of electrical fields of insulation defects by finite element method in the program ComSol. Results. A strong influence of the power supply on the value of voltage surge in case of emergency has been established. The method of adjustment of this influence is proposed. It was found that the oscillatory form of the PD is mainly determined not by the parameters of the insulation defect, but by the parameters of the energy object in which this defect is observed. Method for separation of aperiodic signal of PD from oscillatory component of system transient process in PD is proposed. It is shown that in operating turbogenerators and power transformers the unambiguous connection between the phase of PD occurrence and the voltage of PD occurrence is broken. Method of determination of PD occurrence place in slot part of turbogenerators is proposed. It is shown that in order to increase the reliability of comparing PD in polymer insulation of power cables of different voltage classes and geometric dimensions, when calibrating the measuring system, it is necessary to take into account the speed of propagation of the PD pulse through the cable and the capacity of the cable length unit. The concept of a corrective coefficient for calibration has been introduced and a method for determining it has been proposed. Conclusions. Taking into account the differences in PD parameters in real objects of the electric power industry, proposed in the article, from the parameters obtained in the standard laboratory model of the PD should increase the information and reliability of the PD method, as well as make it possible to conduct a comparative analysis of the results obtained under various observation conditions.
Highlights
The main reason for the irreversible deterioration of insulation properties under the influence of electric fields are electrical discharges in insulation defects, which bypass part of the insulation and are called partial discharges (PD) [1]
Tens of thousands of specialists in the world deal with insulation diagnostics, studying the characteristics of PD in insulation (PD method), in order to predict the time to the occurrence of an emergency due to breakdown of the insulation and closure of the current-carrying phase of the equipment to the ground
If with small sizes of the observation object in the laboratory, the voltage at all points of the high-voltage electrode is the same, when connecting the windings of three-phase turbine generators (TG) and power transformers (PT) into a "star" or "triangle," the amplitude of sinusoidal oscillations in different parts of the winding varies from zero to amplitude phase or interphase value. If it is not known in which part of the winding PD occurs, and this is the case in the vast majority of equipment, the concept of the phase of the occurrence of PD loses the meaning of the occurrence voltage and is not related to the size of the defects
Summary
The main reason for the irreversible deterioration of insulation (aging) properties under the influence of electric fields are electrical discharges in insulation defects, which bypass part of the insulation and are called partial discharges (PD) [1]. If with small sizes of the observation object in the laboratory, the voltage at all points of the high-voltage electrode is the same, when connecting the windings of three-phase TG and power transformers (PT) into a "star" or "triangle," the amplitude of sinusoidal oscillations in different parts of the winding varies from zero to amplitude phase or interphase value If it is not known in which part of the winding PD occurs, and this is the case in the vast majority of equipment, the concept of the phase of the occurrence of PD loses the meaning of the occurrence voltage and is not related to the size of the defects. A study of such differences and problems of PD observation is given in this work
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