Natural Ester Fluid Research Articles

Reclaiming of in-service natural ester-based insulating fluids

The degradation of in-service natural ester-based insulating fluid could result in oil viscosity, acidity and dissipation factor increases. In this work, natural ester-based insulating fluid samples aged in the laboratory and in-service (collected from a Recloser) were reclaimed with different adsorbent materials. All the tested samples showed some properties above the provisional limit for triggering prompt additional investigation suggested by the IEEE guide for in-service natural ester fluids, such as viscosity increase >; 10% from value at time of initial energization, acid number >; 0.3 mg KOH/g or dissipation factor at 25°C >; 3%. The reclamation process was accomplished by the use of two methods: 1) by mechanical agitation of the aged oil in the presence of several adsorbents and 2) by percolation of the aged oil through the adsorbent material. The reclaimed fluids were monitored by evaluation of viscosity, acid number and dissipation factor and the results were compared with unused oil. The results showed that viscosity is the main criterion to evaluate whether or not in-service natural ester-based insulating fluid can be reclaimed.

Winding Temperature Measurement in a 154 kV Transformer Filled with Natural Ester Fluid

This paper measures the hot spot temperatures in a single-phase, 154 kV, 15/20 MVA power transformer filled with natural ester fluid using optical fiber sensors and compares them with those calculated by conventional heat run tests. A total of 14 optical fiber sensors were installed on the high-voltage and low-voltage windings to measure the hot spot temperatures. In addition, three thermocouples were installed in the transformer to measure the temperature distribution during the heat run tests. In the low-voltage winding, the hot spot temperature was , calculated by the conventional heat run test. However, the hot spot temperature measured using the optical fiber sensor was between turns 2 and 3 on the upper side of the low-voltage winding. Therefore, the hot spot temperature of the low-voltage winding measured using the optical fiber sensor was higher than that calculated by the conventional heat run test.

Fault gas generation in natural-ester fluid under localized thermal faults

In this article, the generation of fault gases in FR3 fluid was investigated under various thermal stresses using a sealed vessel with full fluid circulation, and the results were compared with Gemini X under similar conditions. The DGA measurements from an online dissolved-gas monitor were generally comparable with laboratory analysis. The FR3 is more thermally stable than Gemini X, as indicated by less free gas-bubble formation, less violent fluid convection, and less fault gas generation above 300°C.

Hot spot temperature for 154 kV transformer filled with mineral oil and natural ester fluid

This paper deals with the hot spot temperature of a transformer when filled with mineral oil, and later on, with natural ester fluid. 14 optical fiber sensors were installed in the 154 kV, 15 MVA transformer filled with mineral oil, with the hot spot temperature measured during the heat run tests. The transformer was retrofilled with natural ester fluid, after which the hot spot temperatures were measured again. For the rated power, the hottest spot temperature was 105.9 °C when the transformer was filled with mineral oil and 129.4 °C when it was filled with natural ester fluid. The hot spot temperature increased by 23.5 °C in the transformer filled with natural ester fluid. This paper applies the hot spot temperature measured using optical fiber sensors to the life curve in natural ester by McShane et al. The life curve of the thermally upgraded kraft paper in natural ester fluid was compared with that in mineral oil, as suggested by the IEEE guide. The life of the transformer filled with natural ester fluid was similar to that filled with mineral oil. Therefore, transformers filled with natural ester fluid do not require increase of cooling pump capacity and surface area of the radiator or reduction of the load to obtain the same life as that of the mineral oil.

A survey of aging characteristics of cellulose insulation in natural ester and mineral oil

The article makes a case for allowing higher temperatures in transformers filled with natural ester fluids. This article will first provide a review of data from aging studies performed on cellulose (both Kraft paper and pressboard) impregnated separately in mineral oil and BIOTEMP (ABB, USA), a high oleic sunflower based fluid. Next, possible mechanisms that explain the differences in aging behavior will be discussed. The article concludes with recommendations for new temperature limits for BIOTEMP-impregnated transformers in comparison with mineral-oil-impregnated transformers.

Further studies of a vegetable-oil-filled power transformer

In this paper, data obtained from a transformer fitted with an online monitoring system, and using FR3 vegetable oil, were presented. The concentration of water dissolved in the oil was initially around 15 ppm, increased to 25 ppm, and then decreased to 15 ppm over a period of two years. These levels are higher than the levels expected in mineral oil because of the higher hygroscopy of vegetable oil. Ethane was found in a nominally identical transformer that had not been used for two years. This observation supports the hypothesis proposed in previous work that ethane can be generated in FR3 fluid even under no-fault conditions. In the operating transformer the ethane concentration increased during the first month of energization and then decreased to a constant value. The DDF did not vary significantly between oil samples taken from the operating transformer. In the IEEE Guide for Acceptance and Maintenance of Natural Ester Fluids in Transformers, a maximum value of 0.005 at 25 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ο</sup> C is suggested for unused vegetable oil in new equipment. The corresponding value in the operating transformer was around 0.003 at ambient temperature.

배전용 변압기에서의 고온열화와 열 사이클 열화에 따른 식물유와 광유의 특성 분석

Most transformers use insulating and cooling fluids derived from petroleum crude oil, but mineral oil has some possibility of environmental pollution and fire with explosion. vegetable oil fluids extracted from seed has superior biodegradation and fire-resistant properties including an exceptionally high fire point enhancing fire safety. In this study, it is aimed at the practicality of substituting natural ester dielectric fluid for mineral oil in liquid insulation system of transformers. As a rise in coil winding temperature has a direct influence on transformer life time, it is important to evaluate the temperature rise of coil winding in vegetable oil in comparison with mineral oil. Four transformers for the test are designed with 10KVA, 13.2㎸, one phase unit. The temperature are directly measured in insulating oil of these transformers with the two sorts of natural ester and mineral oil dielectric fluid respectively. Experiment for aging carry out two means. First means remained 120℃ that transformer of mineral oil were operated at 185% load. Second means is that insulating oils of two natural ester and mineral oil were aged by thermal cycles repeating from 30℃ to 120℃. For the heating, Transformers were operated at 185% load. For the cooling, cooling system was operated in the chamber. Samples were analyzed at 42, 63, 93, 143, 190, 240 300cycles. Analysis contents are dielectric strength, total acid value. Mineral oils compared results of first means with results of second means. And compared two sort natural esters respectively with mineral oil in second means.

Aging markers for in-service natural ester-based insulating fluids

In this work, the degradation process of natural ester-based insulating fluids was evaluated through laboratory aging tests. Two distinct aging methodologies were used: natural ester-based insulating fluids were placed in sealed flasks at 120°C in the presence of Kraft insulating paper containing about 1.5 and 5 wt% moisture; and natural ester-based insulating fluids were aged with and without Kraft insulating paper containing 1.5 wt% moisture in an open system, adding oxygen at different temperatures. The results indicate that viscosity, acid number and dissipation factor are important markers to consider in monitoring service-aged natural ester fluids.

Decay products in the liquid insulation of power transformers

There is a general agreement that in service conditions the quality of insulating fluids gradually deteriorates under the impact of electrical, thermal and chemical stresses. An important side effect of oil gassing related to the invisible colloidal suspensions is also investigated. Two ASTM methods are used to monitor the deterioration of liquid insulation step by step. The results obtained using a laboratory-grade spectrophotometer and a ratio-turbidimeter indicate that the absorbance increases by a significant and easily observable margin with ageing rate. A comparison is made between the performances of a naphtenic commercial-based mineral oil and a synthetic and natural ester fluid. Under the same aging condition, the obtained results indicate that esters have a better capability to dissolve sludge. Currently, the gassing of oil is solely related to hidden incipient electrical failures. Consequently, these are detected and diagnosed by periodic dissolved gas analysis. The results performed in laboratory conditions reported in this contribution on oil stability under electrical stress indicate that, undetected oil-born decay products contribute to the gassing of oil.

Comparative PD pulse burst characteristics of transformer type natural and synthetic ester fluids and mineral oils

The partial discharge (PD) pulse burst behavior in natural and synthetic organic ester fluids and mineral oils of the type used in transformers has been examined, using simultaneous wide and narrow band measurement techniques. This permitted the determination and comparison of both the overall charge transfer of the PD pulse as well as that of the discrete PD pulses comprising the PD pulse burst in the evaluated dielectric fluids.

Lightning Impulse Testing of Natural Ester Fluid Gaps and Insulation Interfaces

A significant amount of lightning impulse breakdown and withstand testing has been accomplished in mineral oil to understand this important electrical characteristic for transformer insulation system design. To be considered as viable insulating fluids for high voltage equipment, alternative dielectric liquids should have similar lightning impulse characteristics as compared to mineral oil to provide the clearances necessary for common dielectric design. This paper reviews the testing for establishing the lightning impulse breakdown characteristics of natural ester fluids relative to mineral oil test results. The key variables of the testing included: various oil gap and solid insulation creep distances, electrode configurations, electrical stress characteristics, and solid insulation surfaces. The fluid gaps ranged from 3 mm to 55 mm. The electrode configurations included quasi-uniform in oil gaps, with some attached to pressboard, and nonhomogeneous contacts in oil gaps combined with a phenolic interface. The range in gap distance was selected to reflect the range commonly used in liquid insulated transformer core/coil designs. The electrical stresses used included 1.2 × 50 μs lightning impulses of both positive and negative polarity. The solid insulation materials consisted of high density pressboard, Kraft paper and a high density phenolic composite. It is concluded that the impulse breakdown voltage of the natural ester fluid is similar to mineral oil for the oil gaps and electrode configurations tested.

Seed-oil-based coolants for transformers

This article presents information on the safety, reliability, and environmental performance of natural ester transformer fluids by acquainting the readers with the history of transformer fluids and also explores how the industry has arrived at the current technologies of natural ester fluid. The properties of natural ester fluids are explained and then compared side by side with conventional mineral oil fluid. This article outlines two refinery case studies. The first case study is from a refinery in Texas City, where natural ester transformers were chosen for a new wet gas scrubber project. The second case study is from a refinery in Memphis, Tennessee, where natural ester fluid was used to retrofill an in-service, large-power transformer. These two case studies show the applicability of natural ester fluids in new and retrofilled distribution and power class transformers.

Vegetable-oil-based dielectric coolants

Electrical transformer insulation systems are evaluated based on economic, safety, and environmental standpoints using total life cycle analysis. Because of the inherent high efficiency of liquid-cooled transformer designs, new developments focus on improving the environmental and safety properties of fire resistant (less-flammable, high fire point) fluids. This article reports the latest findings on dielectric systems using natural ester (vegetable oil) fluids. Because esters naturally have lower oxidation resistance than mineral oils, a novel blend of base oils and additives were developed to overcome this potential handicap. Single- and three-phase prototype field installations using these new dielectric coolants are discussed.