Effect of Aromatics and Polar contaminant of Natural Ester Oil on Dielectric Strength and Breakdown Time in Mineral Oil under Lightning Impulse Voltage Excitations

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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Streamer propagation in a non-uniform electric field under lightning impulse in short gaps insulated with natural ester and mineral oil

Bulletin of the Polish Academy of Sciences Technical Sciences ◽

10.1515/bpasts-2016-0019 ◽

2016 ◽

Vol 64 (1) ◽

pp. 171-179 ◽

Cited By ~ 4

Author(s):

P. Rozga

Keyword(s):

Light Emission ◽

Experimental Studies ◽

Mineral Oil ◽

Uniform Electric Field ◽

Light Pulses ◽

Streamer Propagation ◽

Lightning Impulse ◽

Small Electrode ◽

Acceleration Voltage ◽

Natural Ester

Abstract This article describes the comparative experimental studies on streamer propagation in natural ester and mineral oil under a high voltage lightning impulse. These studies were concentrated around the small electrode gaps and the point-plane electrode arrangement. The spatial shapes of the developing streamers, light emission and propagation velocity were analyzed and compared between the two different dielectric liquids. In both of them two streamer propagation modes were registered during the studies performed. Propagation of slow 2nd mode streamers took place below the so-called acceleration voltage while fast 3rd mode streamers developed at acceleration voltage and above. Comparing the streamer shapes corresponding to a given voltage polarity, no visible differences were observed between the liquids tested. Concerning the light emission, higher frequencies of light pulses were registered however in the case of natural ester. The significant differences between both liquids were noticed in the value of the acceleration voltage estimated. In the case of positive polarity streamers started to develop in natural ester as a 3rd mode at lower value of testing voltage than in the case of mineral oil. For negative polarity, within the applied testing voltages, 3rd mode streamers appeared only in natural ester. On this basis, the fundamental conclusion is that natural ester may have a lower ability of preventing the development of fast and energetic 3rd mode streamers, even at small electrode gaps.

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Fillers in Electrical Papers for Power Transformers

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.875-877.335 ◽

2014 ◽

Vol 875-877 ◽

pp. 335-340 ◽

Cited By ~ 1

Author(s):

Primo Alberto Calva ◽

Aarón Israel Díaz ◽

Hugo Martínez Gutierrez

Keyword(s):

Electrical Properties ◽

Theoretical Analysis ◽

Structural Parameters ◽

Dielectric Strength ◽

Mineral Oil ◽

Dielectric Behavior ◽

Power Transformers ◽

Mechanical Resistance ◽

Kraft Paper ◽

Natural Ester

The electric papers have a wide variety of uses like in transformers, cables and power capacitors. Each application involves different requirements related to its mechanical and electric properties. The kraft is the dielectric paper most used due its high mechanical resistance and a dielectric strength of around 5 kV/mm that is increased up to 30 kV/mm when is impregnated with mineral oil and typically has a density of 0.7, nevertheless continuous improvements in the design, for example, of power transformers raise the need to improve its electrical properties particularly those related to its relative permittivity. In this article, structural parameters such as distribution and pore size of kraft paper and theoretical analysis for possible addition of nanofillers to improve their dielectric behavior are reported. A possible and better criterion for designing transformers can be the employment of kraft paper nano-inserted with 5 % of TiO2 or BaTiO3 stew in mineral oil and immersed in natural ester liquid.

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Behavior of Biodegradable Oil under Impulse Voltages

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.785.320 ◽

2015 ◽

Vol 785 ◽

pp. 320-324 ◽

Cited By ~ 2

Author(s):

Nurul Izzatul Akma Katim ◽

Mohd Taufiq Ishak ◽

A.M. Ishak ◽

M.Z.A.A. Kadir

Keyword(s):

Breakdown Voltage ◽

Palm Oil ◽

Coconut Oil ◽

Mineral Oil ◽

Electrical Performance ◽

Uniform Field ◽

Testing Methods ◽

Environmental Compatibility ◽

Impulse Voltage ◽

Lightning Impulse

The properties of Palm Oil (PO) and Coconut Oil (CO) offer the potential for transformers with non-toxicity, high fire and flash points and better environmental compatibility while compared with those filled with Mineral Oil (MO). This potential has led to intensive studies of electrical performance of biodegradable oil especially in evaluating the electrical performance under lightning impulse voltage in recent years. This paper presents the investigation on the impulse breakdown voltage of PO and CO in such a uniform field. The PO used in this study is Refined, Bleached and Deodorized Palm Oil (RBDPO) Olein type. Two testing methods, rising-voltage and up-and-down are considered for both oils with different gap distances (2.0 mm and 3.8 mm). Testing methods including rising-voltage method and up-and-down method have no notable influence on the breakdown voltages of RBDPOs and CO compared to MO.

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