Enhancement of Dielectric Properties of Echo-Friendly Cottonseed Oil-based Nanofluids for High Voltages

: This study investigates the performance of nanofluid-based vegetable oil (VO) as an advanced dielectric medium for high-voltage equipment, with a specific focus on AC breakdown voltage (AC BDV). Nanofluids, comprising carefully selected nanoparticles (including Al 2 O 3 , TiO 2 , Fe 2 O 3 , SiO 2 , and Graphene) dispersed in cottonseed oil (CSO), offer a unique opportunity to enhance the dielectric properties of insulating fluids. Through a systematic experimental approach, AC BDV tests were conducted in Khwaja Fareed UEIT High Voltage Laboratory, and the results were compared to with traditional mineral oil (MO) for high-voltage equipment’s. The findings reveal significant improvements in the AC BDV of the nanofluid, demonstrating its enhanced electrical insulation capabilities. This study displays nanofluids based on VO as a promising alternative for enhancing high-voltage equipment's electrical performance while considering the environment. Implementing nanofluids effectively improves the dielectric properties of insulating fluids, contributing to advancements in high voltage equipment technology.


Introduction
High voltages (HVs) immersed in oil frequently use insulating fluids, which depend on MO.MO is inexpensive, serves a dual purpose as an insulator and a cooling agent, and is quite efficient at both.The limited availability of MO, which is mainly made from petroleum products, has sparked heated debate about the long-term viability of transformer oil.Also, their (MOs) dielectric breakdown voltage is modest, and they have poor flash and fire points.Failure to comply with health and environmental regulations is the most significant of these issues.It takes a very long time for their spills to degrade because they are neither biodegradable nor organic [1].
Due to these difficulties, people are more interested than ever to find new solutions, preferably creative and sustainable ones, using already available resources.Using natural esters derived VOs as insulating fluids is one of the most suggested alternatives.A potential alternative to mineral insulating oils in high-voltage oil-immersed power transformers is natural ester insulating (NEI) oils, which slow the deterioration of insulating sheets and get attention of both academics and businesses [2], [3].The difficulties associated with traditional MOs as insulation fluids have prompted an increasing interest in alternative solutions that are derived from readily available resources and offer significant long-term advantages [1].Insulating fluids for high voltage (HV) equipment made of synthetic and natural esters have been the center of attention over the past twenty years, thanks to arising environmental awareness.This is due to the fact that ester liquids are not only non-toxic but also biodegradable, making them a safer alternative to mineral oil, and are one potential answer [2,3].The varied range of esters presents different characteristics, including BDV, density, viscosity, and thermal conductivity, which primarily depend on whether they are sourced from natural or synthetic origins and the constituents present within them.Most natural esters consist of a minimum of 95% VO as their base, with the remaining percentage comprising additives to enhance specific properties [4].When compared to papers impregnated with MO, applying natural esters was determined to be effective in meeting these criteria based on results from accelerated life testing, field experience, electrical and thermal attributes, material compatibility, and performance [5]- [7].Among all esters, MIDEL 1204 and 1215 exhibited lower annual loss of life compared to MO, while MIDEL 7131 demonstrated the lowest annual loss of life [3].
While vegetable oil-based insulating oils have several advantages, such as those mentioned above, they also have the disadvantages of having greater pour points, increased viscosity, and poorer aging, making the oils susceptible to oxidation when compared to conventional mineral oils.Antioxidants have been added to VO as additives to improve their important properties, especially when subjected to thermal aging conditions [8], [9].Another big problem with using VO extensively as an insulating fluid is that it can deplete food supplies when extracted from edible sources.
There will be tremendous expansion in Pakistan's energy sector, and the country is expected to surpass all others in terms of growth rate.Improvements to the power transmission and distribution (PTD) infrastructure are a primary aim of this development.This has increased the need for transformer oil and, by extension, high-voltage equipment.At the same time, Pakistan has an abundance of non-edible CSO since it is the third-largest producer of cotton in the world [10].Pakistan has a lot of non-edible CSO, which might be used to make commercial-quality insulating fluid that is up to par with what the market requires, especially for transformers.
Due to its biodegradability and lack of toxicity, CSO provides a greener option [11].Not only that, but it's also less likely to catch fire than MO because of its high flash and fire points.Having a high concentration of unsaturated fatty acids makes CSO oxidizable, though.Improving CSO by adding antioxidants or boosting its oleic content [12,13] can help mitigate its oxidation vulnerability.Despite its promise, there has been little investigation into the use of CSO as an alternate insulating fluid for transformers.However, it complies with conventional standards for acid and copper strip corrosion and has been proven in some investigations to be compatible with components used in transformers [14].Remember that compared to other natural esters, CSO has a lower BDV [15].
An increasing number of studies have focused on improving insulating fluids' thermal and dielectric characteristics by modifying them with nanoparticles and then creating nanofluids [16]- [19].Different nanofluids have different effects depending on things like particle type, size, shape, agglomeration rate, and filling % [20]- [24].
Nanofillers can be categorized into three main types: carbon-based compounds, metal oxides, and metals.The electrical characteristics of base fluids can be enhanced by adding nanofillers made of metal oxides [25,26].Nanofillers made of carbon, on the other hand, improve the fluids' thermal characteristics.Carbon nanotubes (CNTs) are one type of nanofiller that has received a lot of attention, even when used in small amounts [27].CNTs are able to aggregate amongst carbon nanotube fibrils due to their 1-D structure and Van der Waals π-π stacking surfaces.Functionalization with strong acids is required to prevent CNT aggregation, while it causes unintentional flaws in the continuous sp2-bonded carbon structures.A considerable decrease in thermal conductivity occurs due to these flaws, which increase phonon dispersion [28], [29].
Researchers have focused on creating two-dimensional (2D) materials like graphene and NbO2 to tackle these issues [30], [31].Because of the sp2 covalent interaction between carbon atoms, graphene, which has 2D characteristics and a hexagonal carbon lattice, displays extremely high heat conductivity [32].Nanofillers made of carbon, which is 2D, are ideal to improve the overall quality of high-voltage oil since they contribute to better electrical insulation [33].
In this research, we propose CSO as a high-voltage insulation compared to natural esters (derived from food sources) which suffer from various limitations.The study suggests adding nanoparticles like Al2O3, TiO2, Fe2O3, SiO2, and graphene to the oil (at 50×10 -3 wt./vol% concentration), coupled with Oleic Acid and Ethanol surfactant mixture (by 1:5 ratio), to improve the oil's dielectric and thermal properties.We chose these additions because they have a track record of helping the final nanofluid have the qualities we were hoping for.Researchers evaluated the breakdown voltage and chemical characteristics (including fire point, flash point, cloud point, pour point, and viscosity) of nanofluids synthesized using one-step and two-step procedures, respectively.The synthesis technique was described in great detail.Both approaches were used to introduce different nanofillers at the same concentration so that the results could be compared.Compared to the base CSO, the dielectric and thermal properties of cottonseed nanofluids were assessed, and their dispersion stability was examined in detail.To uncover the basic mechanism, the collected results were examined.

Materials
An oil mill located in the vicinity of Rahim Yar Khan (RYK), Pakistan, purchased cottonseed from a farmer in that area and processed it into oil.We imported the nanoparticles from China for production.They include oxides of silicon, titanium, ferric and aluminum, i.e., SiO2, TiO2, Fe2O3, Al2O3, and graphene.The preparation technique is exploited in the following subsection.

Preparation Technique
The two-step method is another technique used for the preparation of nanoparticles.In this method, the first step involves the synthesis of a precursor solution, which is then used as the basis for the second step, where the nanoparticles are actually formed.Improved control over nanoparticle size and form is one benefit of the two-step process.The reason behind this is that the forerunner solution can be adjusted to suit particular circumstances that promote the creation of particular nanoparticle types.
Multiple methods exist for completing the two-step process; some examples are the microemulsion, sol-gel, and hydrothermal method.The sol-gel process begins with a sol, or colloidal suspension, and ends with a solid substance that has been gelatinized.Two incompatible liquids are merged with a surfactant in the microemulsion process to produce nanodroplets.Remember that the most common metal alkoxides utilized in sol-gel processes include aluminates, titanates, zirconates, borates, alkoxysilanes and titanates.The hydrothermal method is a way to generate nanoparticles by subjecting them to extremely hot and pressurized environments.
The research utilized five distinct nanoparticles-oxides of silicon, titanium, ferric, aluminum, and graphene, i.e., SiO2, TiO2, Fe2O3, Al2O3, and NbO2-followed by a two-step process-based sol-gel method, as shown in Fig. 1.The two-step method was used in the preparation procedure, with the nanoparticle synthesis and NFs preparation being separated.The following procedures were adopted for every NF: a) Initially, the base liquid is filtered by a micro membrane.(b) Then, 0.75 weight percent of oleic acid is added and mixed with an HS mixer at 13×10 3 rpm for 300 s (5 minutes).b) As a next step, the base oil is mixed with the desired amount of powder nanoparticles.The mixture is then agitated for 20 minutes using the HS mixer.c) Finally, nanofluid samples are subjected to ultrasonication for 120 minutes to improve NP dispersion.
The five NFs were each made with 300 mL of volume and 0.05 g/mL of NPs.The 25 mm solid probe was attached to the ultrasonication apparatus that was used for the experiment; it operated at a frequency of 20 kHz and had a power output of 500 W. In pulsed mode, it ran with a 67% duty cycle and a period of 15 seconds, with the amplitude set at 60%.Overheating and damage to the solid probe could be avoided by allowing the gadget to rest for 10 minutes after every 30 minutes of use.

AC Breakdown of CSO
The BV measurements were done by a HV setup named High Volt in the Electrical Engineering Department at KFUEIT.This setup, as illustrated in Fig. 2, included a 300 mL oil test cell, an adjustable electrode system, and a high voltage generator that could reach 100×10 3 V RMS (@50 Hz), compared to the IEC 60156 standard method (Table 1).A mushroom-shaped high voltage (HV) electrode (diameter: 12.5×10 -3 m and spacing: 2.5×10 -3 m) was used to conduct the BD test.The voltage was increased by 2×10 3 V/s until breakdown occurred, as illustrated in Fig. 3.
In addition, nanofluids (oxides of silicon, titanium, ferric and aluminum, i.e., SiO2, TiO2, Fe2O3, Al2O3) and graphene were tested for BDV with an electrode gap of 2.5×10 -3 m.After six measurements, we had six data points to work within our statistical analysis.Anderson-Darling statistics were used to examine the AC BDV data for 2.5×10 -3 m electrode gaps for conformity to extreme value, Weibull, and normal PDF.To find the voltages that correspond to 1%, 10%, and 50% risk levels, the normal and EV PDFs were utilized.

Results and Discussion
A comparison was made between the nanofluids' average AC BDV measurements and pure CSO.The results showed that the nanofluids had a far higher AC BDV.Nanoparticle addition had no detrimental impact on AC BDV, as summarized in Table 2.At a concentration of 50×10 3 wt./vol%, the nanofluids of CSO with oxides of silicon, titanium, ferric and aluminum i.e., SiO2, TiO2, Fe2O3, Al2O3) and graphene nanoparticles were prepared by a simple mixing process.The AC BDV test results show that adding nanoparticles has a large effect on the BDV of nanofluids.The BDV of the nanofluids with oxides of silicon, titanium, ferric, and aluminum, i.e., SiO2, TiO2, Fe2O3, Al2O3) and graphene was found to be 80×10 3 V, 75×10 3 V, 53.2×10 3 V, 78×10 3 V, and 72×10 3 V, respectively.These outcomes indicate that the addition of nanoparticles can significantly enhance the AC BDV of the nanofluids.Among the tested nanoparticles, the oxide of aluminum exhibits the highest improvement.These results indicate the possibility of using nanofluids containing graphene nanoparticles at 50×10 -3 wt./vol% concentration as an insulating material in HV applications.
The electrical strength of nanofluids, on the basis of CSO, can be greatly enhanced by adding nanoparticles at 50×10 -3 wt./vol% concentration, according to the AC BDV test results.Graphene, in particular, showed excellent results.Under certain electrical stress, an insulator begins to conduct electricity at a voltage known as its breakdown voltage (BDV), which opens a conductivity channel within the material.The testing procedure can cause this number, which indicates the electrical insulation's dielectric strength, to change.Table 2 presents the AC BDV and % increase of nanoparticles.In comparison, Figs. 4, 5, 6, 7, and 8 show the AC BDV results on HMI, respectively, and their comparative outcome are depicted in Fig. 9.But all these values do not include atmospheric correction and safety factors.According to IEC60060-1: 2010, the temperature must be 20 o C, absolute pressure should be 1013 mbar and absolute humidity also must 11 g/m 3 .So, the correction factor (CF) is found for the IEC standard.As the BDV depends on the ambient environmental conditions, standard table values must be converted using a correction factor (IEC 60052: 2002): where;  is the breakdown voltage;  is the breakdown voltage at normal conditions;  is the air pressure;  is the air pressure at normal conditions;  is the temperature in ℃ at normal conditions;  is the temperature in ℃ For measurement voltage below 72.5×10 3 V, no humidity correction is applied.This experiment is purely designed for demonstration purposes, and it is, therefore, recommended must apply humidity correction factor (CF) to all except Fe2O3.
Similarly, the indirect measurement of high AC voltage is carried out by using the capacitive voltage divider with the following principal diagram.Figure 10 shows the circuit diagram of AC BDV measurement, and their rated capacitive values are mentioned in Table 3.While Figs. 11 and  According to the calibration report performance recorded as per IEC 60060-2, the assigned factor when comparing the divider with the reference system is 1358, and this factor is set in the HMI software because it is constant.Minor changes in all results were made by implementing the correction factor (CF), as shown in Table 4 and Fig. 13.

Conclusion
Considering all the findings mentioned so far, they point to the possibility that resistance to degradation, flow behavior, electrical insulation, and stability (chemical), can all be improved when graphene, Al2O3, TiO2, Fe2O3, and SiO2 nanoparticles are added to CSO.More nanoparticles tend to improve electrical insulation and viscosity at higher concentrations, but they can also increase the risk of sedimentation and aggregation; therefore, the exact effects are concentration dependent.To maximize nanofluids' efficacy in various contexts, one must meticulously assess the nanoparticle concentration and characteristics.From the comparison with other nanofluids and traditional MO, having a BD strength of 48×10 3 V (a 66% increase), it is inferred that the proposed CSOs (non-edible) with 80×10 3 V BD strength with Al2O3 (50×10 -3 wt./vol%) green nanofluids are an excellent electrical insulating fluid alternative.This information is supported by Tables 2 and 4. Therefore, these results stress the necessity for additional research into sustainable alternatives to traditional MO for insulating highvoltage equipment in the energy Overall, the findings of the AC BDV test displayed that nanofluids with higher concentrations of nanoparticles exhibited stronger electrical insulating capabilities, as shown by the higher BDVs.

Figure 2 .
Figure 2. Front view of HV LAB.
12 show the reading of temperature and pressure.The divider's scale factor (SF) is calculated with the given equation and as per values tabulated in equation 3.  = ( +  +  + ) /  = (0.3109 + 325.5 + 90 +1.035)/ 0factor of 1341 of the divider does not consider the stray capacitances and the influence of a connected PD measuring device.

Figure 13 .
Figure 13.AC BDV results of cottonseed base nanofluids with correction factor.

Table 1 .
AC BDV measuring standards of IEC.

Table 3 .
AC BDV results with CF.
But the temperature and pressure vary with weather conditions.So, calculate the correction factor (CF) according to equations 1 and 2, which is 0.9878.Corrected values are given in Table4.These values are accurate according to IEC standards and strictly focus on noting down and calculating readings.