Contents
1.4 Sustainable VO
Though very few studies have been reported that the insulating NF results in enhancement of the electric strength, yet stability of the NF is not focused for transformer application [46,47]. Unlike MO based TO ages with the passage of service time, ageing of the insulating NF is not given attention. Studies have not been reported on the effect of ageing on the physicochemical and electrical performance of the NF at real time transformer environment.
Seeking the aforementioned literature of NFs and its application in liquid dielectric for transformer it is observed that, the thermophysical and electrical performance of the insulating NF is improved compared to the base fluid. However, in practical application of insulating NF based TO is a challenge. Studies on NF have not revealed about the effect of ageing on the NF based TO and the experimental validation of the NF application with specific ageing techniques is not given enough attention. Moreover, because of the complications in the stability, biodegradability and insignificant fire resistance capability of MO and MO based NF, VO based liquid dielectric is given importance for the research.
the suitable natural ester oil; it is the potential candidate being TO. Since the oil requirement for the transformers is huge, to meet the requirement of ester oil, edible food crops are to be used to extract the oil for the transformer which is likely to cause the food crises in the future [31]. Commercially available rapeseed and canola-based dielectric fluid have raised the question of its functionality in oxidation related issue and insulating capabilities. Seeking the aforementioned drawbacks related to the thermal stability, oxidation stability, nature of unsaturation and importantly affecting the food requirement, hinders its commercial applications. Therefore, an investigation is also needed to be carried out to evaluate the possible implementation of a non-food crop oil as a dielectric fluid for the transformer.
Hence, it is required to study the option left with the nonedible VO and its application as TO in the context of thermophysical and electrical characteristics. A very few research has been carried out in the field of thermophysical and electrical properties of the VO based TO for the replacement of MO [90-94]. But enough attention is not given on the applicability of nonedible VO as an insulant and coolant.
1.4.1 Nonedible VO
Very few non-food seeds such as Jatropha curcas, neem, mahua, karanji etc. are available for the extraction of nonedible VO. However, a limited study on AC, DC and impulse BDV are carried out on the Jatropha curcas oil. The streamer propagation is also studied for the Jatropha curcas methyl ester [31]. But the research did not reveal the response of heat transfer and other allied physicochemical and electrical properties of the nonedible VO. Hence, in this research work, the development of a new nonedible VO, named karanji oil methyl ester (KOME), as a novel TO is presented. The KOME is derived by the process of two-step transesterification from the crude karanji oil (CKO) extracted for the karanji fruit seeds. The Karanji fruits are drought resistant, semi-deciduous and nitrogen-fixing leguminous tree. It grows about 15-20 meters in height with a large canopy which spreads equally wide [95]. We collected the ripened karanji fruits from the karanji tree available in the IIT Guwahati premises followed by removal of karanji seeds and drying. Then the CKO is extracted from the dried karanji seeds using mechanical expeller. Two-step transesterification process has been carried out to prepare the KOME. The thermophysical (thermal conductivity, viscosity, interfacial tension, flash point, pour point and colour), chemical (moisture content, acid number, iodine number) and electrical (ac breakdown voltage, resistivity, dielectric constant, dielectric loss) properties of KOME are studied and compared with MO. Finally, with the ageing and statistical analysis of ACBDV compared to MO ascertain the chemical and dielectric integrity of the KOME.
Karanji tree is a deciduous medicinal plant, which found in the region of northeastern part of India, Indian subcontinent, south-east Asia to north-eastern region of Australia, Fiji and Japan. Karanji belongs to the family of pea and it has many common names such as Indian beech, Pongam oil-tree, Karanji tree, and Pongamia pinnata tree. It grows in the tropical and subtropical region, which does not require a fertile land. The seeds of the karanji tree are now a day widely used for the biodiesel production as shown in Figure 1.2 [96]. The production of the biodiesel from the karanji seeds is a solution for the energy crises and environmental safety.
Many applications of the karanji trees have been explained in several literatures, for example, conservation of soil water, reclamation of the soil, control of soil erosion, major feedstock for pharmaceutical and cosmetic industries. The production of biodiesel from the seeds of the karanji fruits is the key application involved in the recent past of the research.
The karanji seeds are processed into a suitable biodiesel, which acts as a less polluting fuel compared to petroleum-based oil [97]. The byproduct of the karanji oil cake is treated as a suitable organic fertilizer for organic farming. The implementation of the aforementioned application will strengthen the economy of rural people.
Figure 1.2: Nonedible VO based TO [96].
CKO can be obtained from the extraction process of solar dried karanji seeds. Mechanical expeller is being used for oil extraction. The CKO is further processed into the two-step transesterification process to obtain KOME as an insulating oil for the electrical transformer.
The karanji oil can also be extracted using the soxhlet, cold percolation and Solvent extraction process by taking karanji seeds powder as an input. But in these chemical extraction process, the oil percentage is more compared to mechanical extraction [98].
However, the chemical extraction involves a lot of hazardous chemical treatments, so mechanical expeller is more suitably preferred for the extraction of CKO.