Nouruddeen Bashir

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.

Organo-montmorillonite as an electrical treeing retardant for polymeric insulating materials

This paper presents investigation on the propagation of electrical treeing in silicone rubber samples filled with Montmorillonite (MMT) and Organo-montmorillonite (OMMT) nanoclays as fillers for electrical tree inihibition. Treeing experiments were conducted by applying ac voltage with increasing rate of 0.5 kV per second at power frequency on pure silicone rubber, silicone rubber filled with 1% MMT and silicone rubber filled with 1% OMMT samples respectively and treeing propagation length and inception voltage within 30 minutes aging period were observed. Result from this study showed that the silicone rubber/OMMT sample exhibited the shortest tree length as well as highest tree inception voltage followed by the silicone/MMT sample with the pure silicone rubber having the least electrical performance. This finding suggests the OMMT can be used a filler in polymeric insulating materials for electrical tree inhibition.

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.

Electrical treeing in silicone rubber/organo-montmorillonite

Electrical treeing is one of the main reasons for failure of polymeric materials used in high voltage applications. Treeing is observed to originate at points where impurities, voids, defects, or conducting projections cause excessive local electric field stress in the dielectric. It has been proposed that nanofillers could be employed as an electrical tree inhibitor in polymeric insulating materials. With development of nanotechnology, polymer nanocomposites have drawn much attention, because they are expected to have improved mechanical, thermal and electrical properties over the neat polymer. In this paper, modified nanoclay was used to examine the initiation and propagation of electrical treeing. Effects of electrical treeing on nanocomposites insulating material filled with 1 wt% and 3 wt% of Organo-Montmorillonite (OMMT) were used in this work. The results have shown that electrical tree growth was suppressed in silicone rubber nanocomposites compared with neat silicone rubber which allowed a faster growth of electrical treeing. However, more studies should be carried out with different nanofiller/silicone ratios to see in further enhancements in tree inhibition could be achieved.

Techno-economic analysis of hybrid photovoltaic/diesel/battery off-grid system in northern Nigeria

The rate of dependence on stand-alone diesel generator for individual electricity generation among households in Nigeria is geometrically increasing and has thus led to significant increase of the environment pollution. This is due to the inability of the utility company to meet the energy demand of its yearning consumers due to ageing and limitations in power infrastructures. This has led to about 40% of the countrys population been cut off from the national grid. In view of these hazardous effects posed from the usage of these individual diesel-powered generations, this paper reports on the assessment of techno-economic viability of a hybrid photovoltaic diesel/battery off-grid system as an alternative solution to these threats. For that purpose, a remote area located far in the northern part of Nigeria was taken as the case study in which an international institution with peak demand of 90 kW was considered. The HOMER optimization software is used to evaluate both the technical and economic viability of the proposed energy system by taking into account the variations of both the solar radiation and diesel prices, as experienced in most part of Nigeria. The study reveals the potential capability of the hybrid photovoltaic/diesel energy system with battery backup as a good alternative energy source for individual household replacement for diesel-powered generator. In addition, the proposed system is of high energy potential as well as low carbon emission at affordable cost of electricity.

Diagnosis of XLPE Cable using the Recovery Voltage Measurement Method

This paper presents a preliminary investigation on the evaluation of ageing in 11 kV XLPE cable using return voltage measurement (RVM) method. Accelerated ageing using AC voltage was performed on new XLPE cable samples. Within the period of ageing, the state of insulation was investigated and assessed. The result of the diagnosis using the RVM showed a good correlation between aging time and the return voltage initial slopes (dU,/dt) of the aged XLPE cables, indicating the samples have undergone thermal ageing. The RVM technique, which was initially proposed for diagnosis of oil-paper insulation systems, was found to be able to detect ageing in XLPE cables, and thus insulation diagnosis using this technique could be extended to extruded-polymeric insulation systems.

Insulating properties of vegetable oils and their blends

Nowadays researches on the viability of using vegetable-or plant-based oils in power transformers are gaining much attention due to the excellent biodegradability and good dielectric properties they possess. However, studies on their long-term ageing properties and improvement on their dielectric properties is still lacking. This paper reports laboratory studies carried out on 5 different vegetable oils and their blends to investigate their dielectric properties during accelerated thermal ageing. The samples were aged for 120 hours and their breakdown voltage, dissipation factor and oxidative stability investigated. The tradition mineral oil was also investigated in the same fashion for comparison purpose. Results revealed that the vegetable oils insignificant decrease in their dielectric properties. Blending of the oils improved their dielectric properties and oxidation stability. This finding thus suggests vegetable oils possess can good electrical performance during service. Furthermore blending of vegetable oils can be an effective way to improve their oxidation stability.

Electrical treeing initiation and propagation in silicone rubber nanocomposites

Electrical tree initiation voltage and tree propagation length for unfilled silicone rubber, silicone rubber nanocomposites filled with 1% and 3% of OMMT and SiO2 was presented in this paper. This study investigates the capabilities of OMMT and SiO2 in silicone rubber in order to inhibit the growth of electrical treeing. From the result of this study has indicated that in the filled nanocomposite sample, the OMMT acts as barrier to unfilled silicone rubber and silicone rubber filled with SiO2 because the capabilities to decreased the tree propagation length of electrical tree. This result revealed that OMMT could be used as filler in silicone rubber insulating material for the purpose of retarding electrical tree growth.

Statistical study on tree inception voltage of silicone rubber and epoxy resin

Weibull distribution has been used widely by many researches around the world especially in the analysis of high voltage experimental data. Unfortunately, most of the experimental data analysis was not following the accurate statistical technique. Thus in this paper, a statistical study on the tree inception voltage of silicone rubber and epoxy resin is presented. The tree inception voltage of silicone rubber and epoxy resin was measured via camera-equipped online monitoring system. The leaf-like specimen was used as test sample. The experiment was performed based on IEC 1072:1991 “Methods of Test for Evaluating the Resistance of Insulating Materials against the Initiation of Electrical Trees”. The obtained results were analysed statistically by using fitting method. Anderson-Darling goodness-of-fit test was performed in order to obtain the best fitting distribution. Comparison exercise was made between the fitted distribution and Weibull distribution. Based on Anderson-Darling tests, the tree inception voltage of silicone rubber and epoxy resin was best fitted with Johnson SB distribution. Based on this fitted distribution, the value of tree inception voltage for silicone rubber and epoxy resin was calculated and equalled to 3.1529 kV and 4.6528 kV respectively. Thus, it was found that, the fitting method by means of Anderson-Darling goodness-of-fit test was successful to recognize the best fitted distribution for the value of tree inception voltage for silicone rubber and epoxy resin.

Induced voltage on objects under six-phase transmission line

This paper presents results of an experimental investigation on voltage induced on objects under a six-phase transmission line due to line switching incidences. In this work, the voltage induced on a vertical receiver and a pipeline due to line energization and de-energization in a six-phase power transmission line system is reported. The research was carried out using a six-phase transmission line mock-up system with ratio of 5/132 kV. The results showed that the induced voltage on the objects is less than 4 kV. In addition the high induced voltage experienced by the vertical receiver was from the left side of the phase composition while the pipeline experienced higher induced voltage from the right side phase composition.