Partial discharge investigation on palm oil using needle – plane electrode configuration and electric field distribution using ANSYS Maxwell

The Partial Discharge Inception Voltage (PDIV) and PD characteristic of mineral oil were described and compared with palm oil. The test was performed by needle-plane electrode configurations. Both mineral- and palm oil were investigated under AC voltage. A comparison study between PDIV and PD activities of the mineral oil Hyrax and palm oil were investigated with the total volume of the oil in the test cell was approximately 2 L. The 50-μm tip radius of tungsten needle electrodes were utilized as high voltage electrode. On the other hand, the grounded electrode with 30-, 40-, and 50 mm gap distances was represented by a 50-mm and 75-mm diameter copper plane electrode. Consideration on the oil conditions' effect on both PDIV and PD characteristics was also carried out. It was clearly shown that PDIV is dependent on the electric field stress of the electrode system and the test method based on the experimental results. In comparison to differences of gap distance, the 50-μm needle tip radius and 75-mm plane with gap distance of 30-mm electrode revealed the highest electric field stress and inversely exhibited the lowest PDIV value tested. Furthermore, simulation using ANSYS Maxwell on the electric field distributions of the electrode systems was also performed. In order to quantify electric field based on the finite element methods the ANSYS Maxwell was being utilized. In the simulation, the palm oil and mineral oil properties of its 2D modelling test cell was used. From the results, the PD characteristics of mineral oil and palm oil tested by needle-plane electrode system are known. To confirm the suitability of palm oil as a high voltage insulating medium, it is vital to analyse in-depth on its partial discharge activity and characteristics

Ageing effect of vegetable oils impregnated paper in transformer application

Vegetable oils are being considered as potential alternatives to mineral oil, due to their better environmental performance and for their high fire point. Although these liquids have been used in distribution transformer, it is still a significant step to adopt vegetable oils in power transformer due to high cost and high level of safety and reliability required in service for these units. Vegetable oils such as Palm oil (PO), Corn oil (CO), and Rice Bran oils (RBO) offer suitable alternative for mineral oil. It is anticipated that most of the un-aged oil could satisfy the minimum requirement for dielectric insulation liquids in transformer. However, since transformers in service could be subjected to heat and multiple environmental parameters, the oil could be subjected to ageing. The chemical properties of the oil may change and its performance could be affected by the presence of ageing-by-products such as moisture and acids. Therefore, considering the application of new dielectric insulation liquids such as PO, CO and RBO in transformer, it is crucial to first examine its ageing performances at laboratory level. This paper focused on the effect of ageing on the electrical and physicochemical properties of PO, CO, and RBO. Sealed ageing experiments were set at 90°C for 30 days, 90 days and 180 days. Before the ageing process, the samples were dried in a vacuum oven at pressure less than 0.8kP at 85°C for 48 hours in order to remove the moisture content in the oils. Then the oils were impregnated with the Kraft paper and continue to age for selected duration time. The electrical properties (relative permittivity, dielectric losses, resistivity and breakdown strength), mechanical properties (viscosity and tensile strength) and chemical properties (moisture and acidity) of the oils were measured throughout the ageing periods. It can be concluded that the laboratory accelerated thermal ageing experiment reveals that all vegetable oils in this study are resistant toward oxidation based on the stable viscosity and low acidity measurements of vegetable oils throughout the ageing duration even with the presence of oxygen. The AC breakdown voltages of vegetable oils can still comply with the recommended limit of new vegetable oil set by ASTM 6781 even after subjected to ageing. In general most of properties of vegetable oils are comparable with mineral oil

Dissolved gas analysis (DGA) of vegetable oils under electrical stress

Dissolved gas analysis (DGA) is often use by the utility companies to monitor the health and to detect any faults of their transformers. The concentration and proportion of various gases dissolved in the oil are used to indicate whether there is an electrical or thermal fault within the transformer. A lot of data have been published in the literature on DGA levels for a mineral oil. However, the data for vegetable oils are relatively sparse even though the vegetables oils have been used for more than 10 years in distribution transformers. In this paper, the concentration of dissolved gasses under electrical performance in rice bran oil (RBO) and palm oil (PO) were investigated. These two oils were selected since they show promising potential as alternative insulating dielectric liquid for transformer and easily obtained in Malaysia. Three different gaps (2.5mm, 5mm and 10mm) with sphere to sphere configuration were used in this study. The samples were filtered for three times and dried at 85°C for 48 hours before testing. The AC breakdown experiments were performed in the high voltage laboratory for 100 times. The dissolved gasses from the electrical breakdown voltages were obtained in 2 liter sealed test cell. The gasses concentrations were measured using Gas Chromatography equipment. There were six concentrations of gases contained in the samples which are Hydrogen (H2), Methane (CH4), Ethane (C2H6), Ethylene (C2H4), Acetylene (C2H2) and Carbon monoxide (CO). These gasses were interpreted using IEC ratio, Roger ratio, Dornenburg ratio method and Duval Triangle method in order to investigate whether the existing techniques are suitable for RBO and PO. From the experiments, C2H2 and H2 were the highest amount of gases detected for all samples. The Duval triangle method is the best method in detecting the fault for these oils under electrical breakdown. However, the ratio methods have some limitation in predicting the faults

Investigation on AC breakdown of vegetable oils with insulated electrodes

Most of power transformer design today is still using oil filled type which laminated iron core with paper insulated copper conductors. Oil is an important part in power transformers as electrical insulation, information carrier and cooling medium. Besides oil, paper insulation also plays important role as dielectric material of transformer. The influence of oil especially vegetable-based oil and paper insulation on the dielectric strength of transformer oil has attracted many researchers to do investigation. This paper presents a study of the quasi-uniform field AC breakdown voltages under bare electrodes, paper insulation for barrier and covered electrodes (to replicate the transformer windings) of Palm Oil (PO), Coconut Oil (CO) and Mineral Oil (MO). The data obtained from all tests were analyzed using Gaussian and Weibull distribution to determine the withstand voltages for each type of oils. The experiments were using test cell as specified by IEC 156 with 2.5 mm gap distance under uniform field

Optimum Electrical and Dielectric Performance of Multi-Walled Carbon Nanotubes Doped Disposed Transformer Oil

This paper intends to prepare a nanofluid sample by suspending Multi-walled Carbon Nanotubes (MWCNTs) at 0.005g/L concentration and analyze the behavior of electrical and dielectric properties based on the International Electrotechnical Commision test method. In order to validate the effectiveness of MWCNT nanofluid, alternating current breakdown voltage (BDV), negative polarity lightning impulse (LI), dielectric permittivity, dissipation factor (DF), DC resistivity and Raman structural measurement are executed accordingly. In the following, an analysis of the statistical distribution using the two-parameter Weibull distribution law of BDV and LI are evaluated at four experimental conditions to predict the probability of breakdown occurring at different percentages. Based on the observation, the MWCNT filler has a substantial effect in improving the BDV and LI characteristics of disposed mineral oil. The permittivity, DF and resistivity performance of MWCNT nanofluid from 25 °C to 90 °C also produces comparable and reliable performance as a fresh transformer oil. As for Raman structure, the revolution of transformer oil by doping MWCNT does not disrupt the original chemical structure of mineral oil. Hence, this study proves the improvement of the electrical and the behavior of dielectric properties and chemical structure of nanofluid, providing a huge contribution towards the development of insulating materials for transformer application

Lightning breakdown voltage evaluation of palm oil and coconut oil as transformer oil under quasi-uniform field conditions

This paper presents lightning (1.2/50 µs) breakdown voltages of palm oil (PO), coconut oil (CO) and mineral oil (MO) in a quasi-uniform sphere to sphere electric field at two gap distances. The type of PO used in this study is Refined Bleached Deodorized Palm Oil (RBDPO) Olein type. The effect of voltage polarities (positive and negative) and testing methods (rising voltage, up and down and multiple level) on the lightning breakdown performance were investigated. The results indicated that lightning breakdown voltages of CO and RBDPO are comparable to those of MO under various test conditions. The results indicated that there is no polarity effect for lightning impulse breakdown tests in a quasi-uniform field. The testing methods, including rising voltage method, up and down method and multiple level method have a notable influence on the breakdown voltages. The effect of the 50% breakdown voltage on rising voltage method, up and down method and multiple level method for RBDPO and CO is comparable to MO. The withstand voltage at 1% and 50% breakdown probabilities were obtained using the Normal distribution fitting on the cumulative probability plot of impulse shots. Based on a normal distribution fitting, withstand voltages 1% breakdown probability of POA were close to the MO. Finally, based on statistical studies and simulation using ANSYS software, the prediction formulas for breakdown voltage for larger gap distances for all samples were derived

Lightning Impulse Breakdown Voltage of Rice Bran Oil for Transformer Application

Transformer oil does not only serve as an insulating liquid, but also in removing heat from the windings and cores. Mineral oil (MO) has been widely used in transformers for more than 150 years. Recently, researchers have attempted to search for alternative insulating oils due to the possibility that MO will run out in the future together with the concern on fire safety and environmental pollution. Among the potential oils is rice bran oil (RBO). This work presents the studies of the lightning impulse (LI) of RBO behavior under various electric fields, gap distances and testing methods. The electrical performances of LI tests show that RBO and Palm Oil (PO) have lower LI breakdown voltage than MO under both uniform and non-uniform electric fields. However, the difference in LI breakdown voltages between RBO, PO and MO are slightly small which is less than 20%. In addition, there is no significant effect in the various testing methods under both uniform field and non-uniform field where the percentages of difference are less than 12% and 8% respectively. The data of LI breakdown voltage were statistically analysed to predict the withstand voltage and 50% breakdown voltage of oil samples by using Weibull distribution. The Weibull distribution of MO, PO and RBO has well fit with the fitting line. Finally, the relationship between LI voltages under a non-uniform field with various parameters of PO and RBO was obtained and proposed. From this work, it can be concluded that RBO shows promising results to be considered as an alternative to MO in transformer applications