Distribution transformer is the most vital component in the power system. Failure of a transformer leads to loss of revenue besides affecting the reliability of power supply to consumers. It can lead to the non-availability of the transformer for a long duration. Due to this, it is important to maintain the good quality of mineral oil. Thus, if the quality of the mineral oil is reduced then its dielectric strength/quality is degraded. Finally, it can affect the services of the transformer, in terms of continuity of power supply. This paper entails the development of a mathematical MATLAB/Simulink model which able to calculate the life cycle of distribution transformer and exact oil changing frequency. With the help of proposed Matlab/Simulink models, the plot curves between furan content formation versus time, pollution index versus time, and dielectric strength of oil versus time are also prepared. The article methodology uses the newly proposed equations, that are in accordance with IEEE standards: IEEE Guide for Loading Mineral-Oil-Immersed Transformers and Step-Voltage Regulators (IEEE Std. C57.91-2011) and IEEE Guide for the Reclamation of Insulating Oil and Criteria for Its Use (IEEE Std C57.637-2015). Then the case study for a 100 kVA distribution transformer is realized. So, with the input values in the Simulink model of load current of the transformer, dielectric constant of oil and flash point of oil we can estimate the life of the distribution transformer. Harmonic load factor in our research work is not included, in order to reduce influence of harmonic load we need to installed the active filter, which is not covered in this paper.

No abstract

The paper presents a nondestructive ultrasonic method of investigating long-rod insulators used on overhead power lines and in substations. A correlation between the degree of degradation of porcelain C 120 and the ultrasonic wave propagation and attenuation parameters was established. The ultrasonic method was used to analyze the quality of groups of line and post insulators after many years of service. Also a new mechanoacoustic method of investigating the stages in the degradation of insulator porcelain was applied. As a result of the investigations carried out on samples of porcelain C 130 the successive stages in the degradation of ceramic insulators during their service life were determined.

In this article, we presented the results of the tests performed on three sets of samples of glass-reinforced epoxy (GRE) core rods used in alternating current (AC) composite insulators with silicone rubber housing. The objective of this examination was to test the aging resistance of the rod material when exposed to direct current (DC) high voltage. We hypothesized that the long-term effects of the electrostatic field on the GRE core rod material would lead to a gradual degradation of its mechanical properties caused by ionic current flow. Further, we hypothesized that reducing the mechanical strength of the GRE core rod would lead to the breakage of the insulator. The first group of samples was used for reference. The samples from the second group were subjected to a temperature of about 50 °C for 6000 h. The third group of samples were aged by temperature and DC high voltage for the same time. The samples were examined using the 3-point bending test, micro-hardness measurement and microscopic analysis. No recordable degradation effects were found. Long-term temperature impact and, above all, the combined action of temperature and DC high voltage did not reduce the mechanical parameters or change the microstructure of the GRE material.