Ester Fluids Research Articles

The Lightning Impulse Properties and Breakdown Voltage of Natural Ester Fluids Near the Pour Point

Recently, researchers have become interested in natural ester fluids, as they are an environmentally friendly alternative to mineral oils. Natural ester fluids are a natural resource made from plants; they have higher biodegradability, flash, and fire points, and a greater permittivity compared to conventional mineral oils. However, natural ester fluids also have a higher pour point, viscosity, and water content. These characteristics can hamper circulation and impair the electrical properties of an oil-filled transformer. A large amount of data has been accumulated over the years in regards to mineral insulating oil involving dielectric breakdown voltage and lightning impulse tests. However, natural ester fluids have not had their electrical properties sufficiently characterized. In this paper, we present an investigation into the characteristics of the electrical discharge development in natural ester fluids and in an oil-filled transformer near the pour points. The experiment results show that the electrical properties decreased according to a decrease in the ambient temperature and freezing time. It was found that the pour point and water content of natural ester fluids have a significant effect on the electrical properties.

The role of NO in the posterior hypothalamus in amygdala‐generated pressor responses in conscious rats

The nitrergic system modulates cardiovascular functions of the central nucleus of amygdala (CeA) and the posterior hypothalamus (PH) which are involved in the central regulation of the cardiovascular system. The aim of this study was to investigate the contribution of nitric oxide (NO) in the PH in eliciting cardiovascular responses produced through electrical stimulation (ES) of the CeA. Rats were implanted with a stimulation electrode and a parenchymal cannula system into the CeA and a parenchymal cannula or a microdialysis probe into the PH. The next day, the femoral artery was cannulated for haemodynamic measurement. The CeA was electrically stimulated to produce cardiovascular response. The nitric oxide synthetase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME; 400nmol/100nl) or artificial cerebrospinal fluid were injected into the PH or the CeA before the ES of the CeA. The dialysates were collected from the PH to determine the L-citrulline and the L-glutamic acid levels. L-NAME injection into the CeA but not to the PH suppressed the increases in the mean arterial pressure produced by the ES of the CeA significantly; however, heart rate was not affected by L-NAME injection into either the PH or the CeA. L-citrulline and L-glutamic acid levels in the PH were shown to be increased by the ES of the CeA. NO is involved between the PH and the CeA which has a considerable role in the central regulation of the cardiovascular system.

Insulating properties and charge characteristics of natural ester fluid modified by TiO2 semiconductive nanoparticles

In order to improve dielectric performance of natural esters, TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> semiconductive nanoparticles were added to obtain an ester-based nanofluid. AC, lightning impulse voltage and partial discharge tests were applied to the natural ester and the ester-based nanofluid to check their dielectric performances. It was found that TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanoparticles can not only enhance AC breakdown voltage of the ester based nanofluid by a factor of 1.3 but also improve the partial discharge properties of the ester based nanofluid compared to that of the natural ester. Pulse electroacoustic (PEA) and thermally stimulated current (TSC) techniques were applied to investigate charge transport and trap characteristic in natural ester and ester-based nanofluid. It reveals that TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanoparticles can accelerate the charge dissipation rate and uniform the electric field and increase the shallow trap density in the ester-based nanofluid. It is proposed that electron trapping and de-trapping processes in the shallow traps could be one of the main charge transport processes in the ester based nanofluid.

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.

Power transformers with environmentally friendly and low flammability ester liquids

To improve personal safety and reduce the environmental impact of electrical power supply, alternative insulation fluids are demanded for large power transformers. With their biodegradability, the fact that they can be produced from renewable resources, and the high fire point properties, ester fluids are becoming potential substitutes for mineral oil. A number of companies offer such alternative insulation fluids, and in many distribution transformers they are already used satisfactorily. So far, however, there is little experience for use of these liquids in large power transformers. Even in proven high-voltage applications with mineral oil, every change in transformer design or materials needs to be evaluated. Changing such a crucial component as the insulating liquid itself, the suitability must be proven most thoroughly. This paper illustrates various issues which must be clarified in order to successfully operate power transformers filled with these environmentally friendly, renewable and barely inflammable insulating liquids.

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.

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.

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.

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.

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.

Effect of chemical structure on the hydrolytic stability of lubricating base oils

Base oils differing in chemical structure, representatives of hydrocarbon fluids, ester fluids, and water-insoluble polyalkylene glycols (PAGs), were tested (ASTM D2619) for comparison of their hydrolytic stability, which was found to depend on both their chemical structure and purity. The variations observed after hydrolytic degradation in oil acid numbers, water layer acidity, and copper (Cu) strip weight are indicative of excellent hydrolytic stability of hydrocarbon oils, very good hydrolytic stability of PAG oils, and good hydrolytic stability of polyolester oils (characterized by high purity and an acid number lower than 0.1 mg KOH/g). The positive effect of steric hindrance around the ester bonds on the hydrolytic stability of polyolesters was substantiated by the results obtained for the oils of a pentaerythrite tetracaproate and pentaerythrite tetra(sec-caproate) structure.

Physical gelation of cellulose acetate propionate solutions mediated by metal carbonyl complexes

The weak physical gelation of cellulose acetate propionate–butyl butyrate solutions as a result of the in-situ decomposition of iron pentacarbonyl complexes was explored. Viscometry and infrared spectroscopy were used to monitor the iron pentacarbonyl decomposition reaction progress and its effect on viscosity. Changes in viscosity in of the cellulosic fluids in general and gelation in particular were found to be dependent upon the environment in which the Fe(CO)5 decompositions occurred. Systems under inert atmospheres exhibited a marked increase in viscosity, while systems under oxidative atmospheres exhibited a general decrease in viscosity. We propose a hypothesis that explains the dependence of the viscosity of these cellulosic fluids as a function of the environmental conditions during the precursor decomposition. Under nitrogen atmospheres, zero-valent nanoparticles with highly reactive surfaces are synthesized, which form weak, transient bonds with the cellulosic polymer. The iron particles, under these circumstances, serve as weak bridges between adjacent polymer chains. Conversely, the primary particles synthesized under an oxidative atmosphere are metal oxides, which are less attractive to the polymer chain and, therefore, do not yield such bridges. This work demonstrates the capability to apply a simple method to control the viscosity of cellulose 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.

Critical Parameters of Gas Cavities in Dielectric Liquids Stressed with High Electric Fields

Electric field stimulates formation of gas-filled cavities on sharp electrodes in insulating liquids which may initiate the dielectric breakdown of these liquids. Using an analytical model based on electrical and thermodynamic properties of fluids, the critical dimensions of gas-filled bubbles in ester fluid and transformer oils stressed with an impulse electric field were calculated. The results obtained in this paper could be important for the optimisation of the application of these liquids in high voltage and pulsed power systems.

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.

PD pulse burst behavior of a transformer type synthetic organic ester fluid

The partial discharge (PD) pulse burst characteristics of a transformer type synthetic organic ester fluid were compared with those of an equivalent transformer type mineral oil. Wide and narrow bandwidth measurements were carried out to determine simultaneously the apparent charge transfers associated with the overall PD pulse burst as well as that of the individual discrete pulses within the PD pulse burst. The PD pulse burst behavior was found to be similar in both insulating liquids. The discharge cavity formation times ranged from 0.5 to 1.5 mus, while the charge transfers associated with the PD pulse bursts in the liquids were found to extend from approximately 5 to 30 pC.

Electrokinetic-Current Corrosion: I. Valves

Less-flammable phosphate ester hydraulic-system fluids replaced hydrocarbon fluids with the advent of commercial jet airplanes in the 1950s. A new problem then called “erosion” of the metering edges of servocontrol valves developed. This “erosion” was determined to be corrosion caused by the generation of electrokinetic streaming currents in the late 1960s. Subsequently it was found that ionically conducting antierosion additives (AEAs) added to the fluids eliminated the erosion problem. The valve erosion problem with phosphate ester fluids has subsequently been virtually eliminated. New experimental results and refined modeling show that the AEAs decrease the zeta potential and thus corrosion, mainly by specific adsorption and electrical double-layer compression, and that the previously proposed back-conduction is insufficient. The concepts described provide a background for investigating other unexplored instances of electrokinetic corrosion such as wear in lubricated systems and chemical polishing.