Abubakar Abdullkareem Suleiman

Temperature effect on electrical treeing and partial discharge characteristics of silicone rubber-based nanocomposites

This study investigated electrical treeing and its associated phase-resolved partial discharge (PD) activities in room-temperature, vulcanized silicone rubber/organomontmorillonite nanocomposite sample materials over a range of temperatures in order to assess the effect of temperature on different filler concentrations under AC voltage. The samples were prepared with three levels of nanofiller content: 0% by weight (wt), 1% by wt, and 3% by wt. The electrical treeing and PD activities of these samples were investigated at temperatures of 20°C, 40°C, and 60°C. The results show that the characteristics of the electrical tree changed with increasing temperature. The tree inception times decreased at 20°C due to space charge dynamics, and the tree growth time increased at 40°C due to the increase in the number of cross-link network structures caused by the vulcanization process. At 60°C, more enhanced and reinforced properties of the silicone rubber-based nanocomposite samples occurred. This led to an increase in electrical tree inception time and electrical tree growth time. However, the PD characteristics, particularly the mean phase angle of occurrence of the positive and negative discharge distributions, were insensitive to variations in temperature. This reflects an enhanced stability in the nanocomposite electrical properties compared with the base polymer.

Faults identification of biodegradable oil-filled transformers based on polarization and depolarization current measurement (PDC) method

Polarization and depolarization current (PDC) measurements of insulation oil alone can be used for faults identification. From measurement of healthy oil conditions at different moisture levels and after faults, fault identification can be achieved by comparing the PDC pattern of an oil sample against the PDC fingerprints. Furthermore, a graph plot establishes a relationship between oil sample conductivity and moisture level as well as between oil samples measured capacitance and moisture level. These curves can be used to evaluate the oil moisture conditions and the fault type. This paper seeks to find the PDC pattern of the biodegradable oil (Envirotemp ® FR3™) at different moisture levels and after being subjected to different types of fault: partial discharge, arcing, and overheating. The experiment was carried out in the laboratory to obtain the PDC patterns generated by the oil. Changes in the PDC pattern of biodegradable oil from its fingerprint due to the increased moisture level in the oil or because of faults that occurred to the oil sample were identified. These can help in predicting the biodegradable oil-filled transformers condition and can give some indication of the maintenance work that should be taken on the transformer.

Wetting characteristics for kraft paper immersed in mineral and biodegradable insulation oils

Moisture in power transformers are undesirable but yet unavoidable; hence necessitating its continuous study. The kraft paper of the oil filled transformer absorbs much of its moisture from the insulation oil in which it is immersed. The dielectric properties of the paper can be determined as a function of the wetting, penetration and saturation of the paper by the aqueous liquid in the oil. This paper compares the absorption characteristics of aqueous substances into kraft paper in two commercial insulation oils; palm based Palm Fatty Acid Ester (PFAE) biodegradable oil and petroleum based Hyrax Hypertrans mineral oil. Kraft paper thicknesses used in this study were varies from 0.2 mm to 0.5 mm and 1.0 mm. Test oil samples are taken directly from drum given by the suppliers. The study result shows that substances absorbed by kraft paper immersed in both insulation oils is dependent on paper thickness and chemical composition of the oils. The result shows that 0.2 mm thick paper absorbs the same aqueous percentage from both insulation oils irrespective of their constituent moisture content while the substance absorbed in both the 0.5 mm and 1.0 mm thick papers immersed in PFAE is higher that immersed in Hyrax Hypertrans by about 1%. It also shows that the rate of absorption reduces as the paper thickness increases. This concludes that irrespective of the high initial moisture content of PFAE being higher than that of Hyrax Hypertans, same aqueous substance is diffused into kraft paper.

Investigation on propensity difference of water tree occurrences in polymeric insulating materials

In case of medium voltage cables, the main cause of the insulation breakdown is water treeing by referring to the report of national power utility of Malaysia, Tenaga Nasional Berhad (TNB). The inconsistent and unreliable nature brings out the importance of research towards water tree detection of polymeric insulating cable. Early detection of water tree in underground polymeric cable is important in order to increase the cable efficiency by reducing the timeframe of the cable failure. From the previous research of water tree detection, the types of needle that have been used are metal and nickel. It was found that the usage of these needles has some weaknesses which lead to inefficiency of water tree detection. Corrosion, losses and corona discharge are some of the significant problems faced by using those materials. In addition to that, it was found that the time was taken longer using the previous method of water tree detection. Thus, in order to reduce the time of water tree detection and preventing the materials physical failures, an improved method is proposed. Also, this paper presents the propensity difference of water tree detection in two different insulating materials namely cross-linked polyethylene (XLPE) and low-density polyethylene (LDPE). With the data and research being studied carefully, the water tree detection will be much easier to detect. The effect of ageing time in water tree detection was also discussed in this paper.

Performance of biodegradable insulating oil under accelerated thermal ageing

Biodegradable insulation oils are gaining acceptable use in power transformers as alternative to the successfully petroleum-based oil. In general all insulation oils must be good as insulators and as well as being good heat exchange media. The ability of the insulation oil to remain physically and chemically stable under thermal stress defines the quality of the oil. Based on this expectation, this paper presents experimental result of study on physical and chemical changes in two commercial biodegradable insulation oils: palm-based Palm Fatty Acid Ester (PFAE) and soybean-based Envirotemp FR3 (FR3). Both were subjected to sustained thermal stress at 150 °C for period of 200 hours to induce accelerated ageing process. The breakdown voltage (BDV) and intrinsic viscosity of both oils are analyzed and presented in this study. Fourier Transform Infrared (FTIR) spectroscopy of the oils was investigated with the aim of studying the physical and chemical changes in the molecular structure of the oils that causes the BDV and viscosity result outcomes. The result shows that the BDV in both oils decrease in the same pattern while the viscosity of the FR3 increased by 10.38 % and the PFAE increased 34.25 % indicating that the PFAE degrades more than the FR3 when both oils are subjected to the same thermal conditions. The FTIR spectra showed significant changes in the peak positions which confirm the thermo-oxidative degradation of the oils.

Design of HV switching for polarization & depolarization current measurement

The method of assessing the insulation condition in high voltage (HV) electrical equipments can never be overemphasized. Over the years, several method of assessing the insulation condition have been researched & used by many researchers. One of these methods is using the dielectric response of the materials to determine the Polarization and Depolarization Current (PDC). PDC is a non-destructive assessment method that combines a sequence of switching operations & current measurement for time domain response. In this paper, the HV switching sequence for a PDC assessment was designed & built to fulfill the PDC assessment basic theory. The switch was applied on three materials used in HV insulation to determine their polarization current (ip) & depolarization current (id). Test duration for both ip & id were 10000 seconds and the test results are presented as a current pattern. The current pattern is consistent with the theoretical current wave PDC pattern from literatures thereby confirming the validity of the built switching device.

Optimal percentage natural rubber blends with Low Density Polyethylene (LDPE) for breakdown voltage (BDV) improvement

Solid insulators made of paper, glass or polymeric are some of the critical materials found in electrical power systems to prevent the flow of charges in undesirable paths. Understanding the behavior of these insulators is therefore important because it enables engineers and electrical equipment designers to develop good solid electrical insulators. In this research, we have studied three solid insulating materials; pure Low Density Polyethylene (LDPE), Standard Malaysia Rubber (SMR 10) and Deproteinized Natural Rubber (DPNR). The study is aimed at understanding behavior when this material is combined. In this project, LDPE was selected as based material and was blended with 0 to 30% of SMR 10 or 0 to 30% of DPNR. The breakdown voltage and tensile strength test were done to determine the dielectric and mechanical strength of the pure and blended materials. The result shows that the electrical strength of LDPE increases as the ratio of adding SMR 10 or DPNR is increased. This discovery proves that the electrical performance of LDPE is better when it is blended with SMR 10 or DPNR. As for mechanical strength, it was found that the strength of LDPE was not affected by increasing the ratio of SMR 10, however it reduced when the ratio of DPNR increases. This study concludes that the use of SMR 10 can improve the electrical performance of LDPE without reducing its mechanical strength. However, the use of DPNR has the disadvantage of reducing the mechanical strength of LDPE even though it increases it electrical breakdown value. As a conclusion, LDPE is better improved by blending it with 0 to 30 % SMR 10 for the electrical insulation purposed.