A review on critical evaluation of natural ester vis-a-vis mineral oil insulating liquid for use in transformers: Part 1

Natural and synthetic esters are liquids characterized by insulating properties, high flash point, and biodegradability. For this reason, they are more and more often used as an alternative to conventional mineral oils. Esters are used to fill new or operating transformers previously filled with mineral oil (retrofilling). It is technically unfeasible to completely remove mineral oil from a transformer. Its small residues create with esters a mixture with features significantly different from those of the base liquids. This article presents electrostatic charging tendency (ECT) tests for mixtures of fresh and aged Trafo EN mineral oil with Envirotemp FR3 natural ester from the retrofilling point of view. Under unfavorable conditions, the flow electrification phenomenon can damage the solid insulation in transformers with forced oil circulation. The ECT of the insulating liquids has been specified using the volume density of the qw charge. This parameter has been determined using the Abedian–Sonin model on the basis of the electrification current measured in the flow system, as well as selected physicochemical properties of the liquids. It was shown that ECT is strongly dependent on the type of insulating liquid and pipe material, as well as the composition of the mixtures. The most important finding from the research is that a small amount (up to 10%) of fresh and aged mineral oil is effective in reducing the ECT of Envirotemp FR3 natural ester.

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Lightning Impulse Withstand of Natural Ester Liquid

Energies ◽

10.3390/en11081964 ◽

2018 ◽

Vol 11 (8) ◽

pp. 1964 ◽

Cited By ~ 9

Author(s):

Stephanie Haegele ◽

Farzaneh Vahidi ◽

Stefan Tenbohlen ◽

Kevin Rapp ◽

Alan Sbravati

Keyword(s):

Breakdown Voltage ◽

Dielectric Strength ◽

Mineral Oil ◽

Homogeneous Field ◽

Inhomogeneous Field ◽

Insulating Liquids ◽

Lightning Impulse ◽

Insulating Liquid ◽

Natural Ester ◽

Inhomogeneity Factor

Due to the low biodegradability of mineral oil, intense research is conducted to define alternative liquids with comparable dielectric properties. Natural ester liquids are an alternative in focus; they are used increasingly as insulating liquid in distribution and power transformers. The main advantages of natural ester liquids compared to mineral oil are their good biodegradability and mainly high flash and fire points providing better fire safety. The dielectric strength of natural ester liquids is comparable to conventional mineral oil for homogeneous field arrangements. However, many studies showed a reduced dielectric strength for highly inhomogeneous field arrangements. This study investigates at which degree of inhomogeneity differences in breakdown voltage between the two insulating liquids occur. Investigations use lightning impulses with different electrode arrangements representing different field inhomogeneity factors and different gap distances. To ensure comparisons with existing transformer geometries, investigations are application-oriented using a transformer conductor model, which is compared to other studies. Results show significant differences in breakdown voltage from an inhomogeneity factor of 0.1 (highly inhomogeneous field) depending on the gap distance. Larger electrode gaps provide a larger inhomogeneity at which differences in breakdown voltages occur.

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Applying HF and VHF/UHF Partial Discharge Detection for Distribution Transformer

Journal of Mobile Multimedia ◽

10.13052/jmm1550-4646.1545 ◽

2020 ◽

Author(s):

Sakda Maneerot ◽

Masaaki Kando ◽

Norasage Pattanadech

Keyword(s):

High Frequency ◽

Partial Discharge ◽

Mineral Oil ◽

Surface Discharge ◽

Distribution Transformer ◽

Impregnation Process ◽

Distribution Transformers ◽

Insulating Liquid ◽

Paper Insulation ◽

Natural Ester

This paper represents application of high frequency (HF) and very high frequency/ultrahigh frequency (VHF/UHF) partial discharge (PD) detection for a distribution transformer. A capacitive sensor is used to detect the HF electric field caused by charge transfer inside oil–paper insulation due to PD at the defect site, and an electromagnetic sensor or antenna is used for detecting electromagnetic PD transients in the air outside the investigated transformer in the near-field region. Three types of artificial PD sources in air and insulating liquid, which are corona discharge, surface discharge and air void discharge in pressboard, were investigated. Three identical distribution transformers were rated at 22 kV, 400 V and 50 kVA, and were designed and constructed. The first transformer was filled with mineral oil, the second was filled with natural ester and the third was filled with palm oil. The PD generated by the air-filled voids in the insulating papers and pressboards of these transformers with five different conditions were investigated, i.e., non-impregnated paper, impregnated paper for 3 hours, 6 hours, 9 hours and 12 hours. The impregnation process was done with 65°C liquid temperature, and the pressure in the oven was around 5 mbar. From the experimental results, it can be concluded that the electromagnetic PD transients radiated from the corona discharge of both high-voltage (HV) and low-voltage sides in the air are in the VHF range, and surface discharge frequency is extended up to the UHF range. For the PD in the insulating liquid, the phase resolved PD (PRPD) pattern in the HF range is a valuable tool to characterize the PD sources. The PD in an air-filled void inside the insulating paper of the mineral oil transformer is obviously different compared with those of the natural ester transformer and the palm oil transformer. For the manufacturing of distribution transformers in this research, it is found that after the paper insulation is dried out, the impregnation process for a period of 9 hours is suitable for improving the oil–paper insulation with an acceptable PD level. This paper is the cross-field application by applying the antenna and communication theory for detecting the discharge problems in HV equipment.

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Investigation of Survival/Hazard Rate of Natural Ester Treated with Al2O3 Nanoparticle for Power Transformer Liquid Dielectric

Energies ◽

10.3390/en14051510 ◽

2021 ◽

Vol 14 (5) ◽

pp. 1510

Author(s):

Raymon Antony Raj ◽

Ravi Samikannu ◽

Abid Yahya ◽

Modisa Mosalaosi

Keyword(s):

Survival Rate ◽

Hazard Rate ◽

Power Transformer ◽

Mineral Oil ◽

Interpolation Polynomial ◽

Distribution Functions ◽

Flash Fire ◽

Predicted Values ◽

Natural Ester ◽

Electrical Apparatus

Increasing usage of petroleum-based insulating oils in electrical apparatus has led to increase in pollution and, at the same time, the oils adversely affect the life of electrical apparatus. This increases the demand of Mineral Oil (MO), which is on the verge of extinction and leads to conducting tests on natural esters. This work discusses dielectric endurance of Marula Oil (MRO), a natural ester modified using Conductive Nano Particle (CNP) to replace petroleum-based dielectric oils for power transformer applications. The Al2O3 is a CNP that has a melting point of 2072 °C and a low charge relaxation time that allows time to quench free electrons during electrical discharge. Al2O3 is blended with the MRO and Mineral Oil (MO) in different concentrations. The measured dielectric properties are transformed into mathematical equations using the Lagrange interpolation polynomial functions and compared with the predicted values either using Gaussian or Fourier distribution functions. Addition of Al2O3 indicates that 0.75 g/L in MRO has an 80% survival rate and 20% hazard rate compared to MO which has 50% survival rate and 50% hazard rate. Considering the measured or interpolated values and the predicted values, they are used to identify the MRO and MO’s optimum concentration produces better results. The test result confirms the enhancement of the breakdown voltage up to 64%, kinematic viscosity is lowered by up to 40% at 110 °C, and flash/fire points of MRO after Al2O3 treatment enhanced to 14% and 23%. Hence the endurance of Al2O3 in MRO proves to be effective against electrical, physical and thermal stress.

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Effect of thermal aging on the dielectric properties of mixture between mineral oil and natural ester

TENCON 2015 - 2015 IEEE Region 10 Conference ◽

10.1109/tencon.2015.7372866 ◽

2015 ◽

Cited By ~ 5

Author(s):

Suwarno ◽

Jusua Marbun

Keyword(s):

Dielectric Properties ◽

Thermal Aging ◽

Mineral Oil ◽

Natural Ester

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Comparative study to understand behaviour of natural ester as transformer insulating liquid

2015 IEEE 10th International Conference on Industrial and Information Systems (ICIIS) ◽

10.1109/iciinfs.2015.7398996 ◽

2015 ◽

Cited By ~ 1

Author(s):

Kapila Bandara ◽

Chandima Ekanayake ◽

Tapan K Saha

Keyword(s):

Comparative Study ◽

Insulating Liquid ◽

Natural Ester

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Effect of Water on Electrical Properties of Refined, Bleached, and Deodorized Palm Oil (RBDPO) as Electrical Insulating Material

Jurnal Teknologi ◽

10.11113/jt.v64.2108 ◽

2013 ◽

Vol 64 (4) ◽

Cited By ~ 1

Author(s):

Nazera Ismail ◽

Yanuar Z. Arief ◽

Zuraimy Adzis ◽

Shakira A. Azli ◽

Abdul Azim A. Jamil ◽

...

Keyword(s):

Electrical Properties ◽

Breakdown Voltage ◽

Palm Oil ◽

Pour Point ◽

Electrical Breakdown ◽

Dissipation Factor ◽

Mineral Oil ◽

Flash Point ◽

Effect Of Water ◽

Insulating Liquid

This paper describes the properties of refined, bleached, deodorized palm oil (RBDPO) as having the potential to be used as insulating liquid. There are several important properties such as electrical breakdown, dielectric dissipation factor, specific gravity, flash point, viscosity and pour point of RBDPO that was measured and compared to commercial mineral oil which is largely in current use as insulating liquid in power transformers. Experimental results of the electrical properties revealed that the average breakdown voltage of the RBDPO sample, without the addition of water at room temperature, is 13.368 kV. The result also revealed that due to effect of water, the breakdown voltage is lower than that of commercial mineral oil (Hyrax). However, the flash point and the pour point of RBDPO is very high compared to mineral oil thus giving it advantageous possibility to be used safely as insulating liquid. The results showed that RBDPO is greatly influenced by water, causing the breakdown voltage to decrease and the dissipation factor to increase; this is attributable to the high amounts of dissolved water.

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